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ATLANTA BRANCH
UNITED STATES
DEPARTMENT OF AGRICULTURE
LIBRARY
Book number 463. 8
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McGRAW-HILL PUBLICATIONS IN THE
BOTANICAL SCIENCES
Edmund W. Sinnott, Consulting Editor
FIELD MANUAL OF PLANT ECOLOGY
Selected Titles From
McGRAW-HILL PUBLICATIONS IN THE
BOTANICAL SCIENCES
Edmund W. Sinnott Consulting Editor
Arnold — An Introduction to Paleo-
botany
Avery et al. — Hormones and Horti-
culture
Babcock and Clausen — Genetics
Boy sen Jensen and Avery and
Burkholder — Growth Hormones in
Plants
Braun-Blanquet and Fuller and Con-
ard — Plant Sociology
Eames — Morphology of Vascular
Plants
Eames and MacDaniels — An Intro-
duction to Plant Anatomy
Fitzpatrick — The Lower Fungi
Gates — Field Manual of Plant
Ecology
Gdumann and Dodge — Comparative
Morphology of Fungi
Haupt — An Introduction to Botany
Haupt — Laboratory Manual of Ele-
mentary Botany
Hill — Economic Botany
Hill, Overholts, and Popp — Botany
Johansen — Plant Microtechnique
Loomis and Shull — Methods in Plant
Physiology
Lutman — Microbiology
Maximov — Plant Physiology
Miller — Plant Physiology
Pool — Flowers and Flowering Plants
Sass — Elements of Botanical Micro-
technique
Seifriz — Protoplasm
Sharp — Introduction to Cytology
Sharp — Fundamentals of Cytology
Sinnott — Botany: Principles and
Problems
Sinnott — Laboratory Manual for
Elementary Botany
Sinnott and Dunn — Principles of
Genetics
Smith — Cryptogamic Botany
Vol. I, Algae and Fungi
Vol. II, Bryophytes and
Pteridophytes
Smith — Fresh-water Algae of the
U. S.
Swingle — Textbook of Systematic
Botany
Weaver — Root Development of Field
Crops
Weaver and Clements — Plant Ecology
Wodehouse — Pollen Grains
There are also the related series of McGraw-Hill Publications in the Zoologi-
cal Sciences, of which A. Franklin Shull is Consulting Editor, and in the
Agricultural Sciences, of which R. A. Brink is Consulting Editor.
Field Manual
of Plant Ecology
by
Frank C. Gates, Ph.D.
Kansas State College and University of Michigan
Biological Station
FIRST EDITION
NEW TORK TORONTO LONDON
McGRAW-HILL BOOK COMPANY, INC.
1949
igftfflMR
6vl
FIELD MANUAL OF PLANT ECOLOGY
Copyright, 1949, by the
McGraw-Hill Book Company, Inc.
printed in the united states of america
All rights reserved. This book, or
parts thereof, may not be reproduced
in any form without permission of
the publishers.
PREFACE
Having taught plant ecology at the University of Michigan
Biological Station during the past thirty-two summers, the author
has acceded to repeated requests for a manual based on this course.
The course was initiated and developed in line with Agassiz's
famous maxim: " Study nature, not books," in addition to which
special effort was made to use as little and as simple apparatus
as possible. The aim was to work with plants at all times.
Both high-school and college students can use the manual with
suitable modification in any part of the country.
At the present time (1949) several excellent books are avail-
able for reference and study. While the author still maintains
that fundamentally the best results are obtained when the novice
explores the subject for himself with a minimum of direction
and instrumentation, he is not blind to the broadening of hori-
zon obtained from consulting certain well-chosen books dealing
with ecology. To name but a few, one may call attention to the
following, of which the first two are excellent textbooks for
vegetational ecology, and the third is most useful for the study
of individual plants.
1. Weaver, John E., and F. E. Clements, " Plant Ecology,"
2d ed., McGraw-Hill Book Company, Inc., New York. 1938.
2. Braun-Blanqttet, J., " Plant Sociology," translated and
revised by G. D. Fuller and H. S. Conard, McGraw-Hill Book
Company, Inc., New York. 1932.
3. Cowles, H. C, " Ecology," revised and enlarged by G. D.
Fuller, American Book Company, New York. 1931.
4. Welch, Paul S., " Limnology" (zoological), McGraw-
Hill Book Company, Inc., New York. 1935.
5. Shelford, V. E., " Laboratory and Field Ecology" (zoo-
logical), The Williams & Wilkins Company, Baltimore. 1929.
6. Clements, F. E., and V. E. Shelford, "Bioecology,"
John Wiley & Sons, Inc., New York. 1939.
V
3 \ ^ \
vi PREFACE
7. Shelford, V. E., compiler and general editor, ' ' Naturalist's
Guide to the Americas," The Williams & Wilkins Company,
Baltimore. 1926.
8. Tansley, A. G., and T. F. Chipp, editors, ''Aims and
Methods in the Study of Vegetation/' British Empire Vegetation
Committee. 1926.
9. Klages, KarlH. W., " Ecological Crop Geography," The
Macmillan Company, New York. 1942.
10. Daubenmire, R. F., " Plants and Environment," John
Wiley & Sons, New York. 1947.
11. Oosting, Henry J., "The Study of Plant Communities,"
W. H. Freeman and Company, San Francisco. 1948.
In the bibliographies in these books the student will find many
references to additional literature.
In using this or any other manual the teacher must study over
the habitats at his disposal and select certain ones for classwork
together with the methods best fitted for that particular area.
He should then " cruise" over the area to become absolutely
familiar with the plants and endeavor to be ready to cope with
any situation that may arise. Sometimes specific directions for
an area will need to be made in addition to the general directions
in this manual. Later in the course, areas new to the teacher as
well as to the students may be studied.
In setting up the field course in plant ecology in a new area,
effort should first be directed toward obtaining as detailed maps
as possible. If such are not available, the teacher should make
some preliminary maps himself to use until better ones can be
obtained. At least one class exercise may be expected to result
in a detailed map of a small part of the region. If the teacher is
familiar with the ground control, aerial photographs are a great
help in locating streams, lakes, roads, and trails but have to be
carefully checked in determining vegetation.
With or without maps, the teacher must explore the area to
discover and evaluate likely places for classwork. He should
make necessary transportation arrangements, determine what and
how much general and special equipment will be needed, and make
direction sheets. The latter should call attention to location
and special features; include questions to direct attention and
PREFACE vii
study; contain lists of species, references, and special pointers
regarding write-up; and state the time at which the report is to
be handed in.
In an area of many possibilities a portion of the work may
take account of particular needs of certain students.
In the field, the teacher will introduce the area by pointing
out its salient features, giving as much of the history as is known
or pertinent; select or assign the work of the students, individu-
ally or in groups; be as available as possible to all for answering
questions, checking directions, etc., and to lead a get-together
in the area as soon as the field work is finished for more question-
ing and to summarize the data.
The student, on the other hand, should learn the time, the
place, and the equipment necessary for the trip; go over the ad-
vance assignment, if there is one; get the direction sheet or the
assignment for his group; complete the work in the field, record-
ing the data in the form most suitable for incorporation in the
data assemblage, make such drawings, sketches, or collections as
are necessary; obtain any special directions for writing up the
exercise ; and hand in the report within the set time limit.
In different parts of the country, the number and variations
in types of vegetation will make it necessary to select exercises
that are suitable to that region. Thus all ecology courses should
not be expected to be alike in the material used, although the ap-
proach and methods of studying may be quite similar.
The greater the diversity present in a region, the easier it is
to utilize successional relationships as the underlying framework
upon which to base the course. In most areas in nature there
will be two feralarch (or wild, i.e., natural) series — the one start-
ing on bare ground as rock, known as the xerarch series, or sere,
and the other initiated in the water of streams, lakes, or ponds,
known as the hydrarch sere. Typical areas of associations from
the early or pioneer stages, mid-stages, and final or semifinal (climax
or subclimax) stages should be selected for study, individually
or in groups. One should be sure to include as many of the follow-
ing types of habitat as feasible :
Forests of different types on different soils, upland and low-
land, rain forest, winter rain or dry forest.
viii PREFACE
Grasslands, as prairies, plains, marshes.
Deserts.
Hydric or aquatic, as lakes, ponds, streams.
Special habitats, as sand dunes, bluffs, strands, riverbanks,
bogs, swamps, marshes, saltmarshes, rock, revegetation
after fire or abandonment.
Under conditions of human disturbance the hemerarch series
is present. The development of orchards; of lawns, pastures,
meadows; of roadsides, rock-gardens, fencerows, vacant lots; or
the conditions of any of the crops of an area may be studied.
Any study of factors, either with regard to individual plants
or to any of the groupings in vegetation, will require the use of
instruments. Specific directions for certain exercises in certain
areas will be made to utilize the various available instruments
one or more times in appropriate situations; hand levels in dune
profiles, soil auger in soil work, tape and benchmarks in dune
movement, steel tape and special compasses in surveying, tree
calipers in forest studies, peat borers in peat study, while meter-
sticks, pH set, and cameras may be used quite generally.
A second year in the same area will make possible necessary
adjustments and improvements and will also serve as a check on
past work. A series of years in the same region will permit the
building up of a historical account of the vegetation and serve
as a check on any predictions that may have been made.
It is at once obvious that it will not be possible to do all of
the exercises in this manual in one season or one summer. It is,
however, essential that the work include thorough grounding in
the quadrat method in some of its forms. Tree counting, tran-
sects, charting, an exercise in mapping, familiarity with the main
factors of the environment, characterization of the dominant
species of the associations, and successions between the associa-
tions are fundamental and should certainly be included. At
least three formal reports should be written.
At the University of Michigan Biological Station, where 16
full days are available each summer, the following program has
been carried out: work in the aspen association, employing dif-
erent quadrat and tree-counting methods, soil characterization,
recovery from previous fires, community coefficients and species
PREFACE ix
analysis, on 4 days; in bogs another 4 days, studying the asso-
ciations and their successional relationships in changing the bog
from open water to land, work with peat; in sand dunes for 2
days, including a study of the development of dunes, the root
and shoot systems of their characteristic species and a profile of
the surface of the ground; aquatics for 1.5 days, during which
the different groupings with the characteristics of their typical
species and successional relationships are studied in lakes, streams,
and beachpools; the maple-beech forest for 2 days, including
a study of the dominant and characteristic ground plants, soil,
and reproduction; surveying and map making 1 day; the jackpine
association on 1 day, including the growth of the dominant spe-
cies, the characteristic ground flora, and the successional rela-
tionships; and 0.5 day devoted to examinations. Two longer
and two shorter written papers are required during the summer.
The author is indebted to Nellie B. Jacobs for many hours
of stenographic work in connection with the production of this
manual and to his wife, Margaret T. Gates, for her inspiration
and assistance in the preparation of the manuscript.
Frank C. Gates
Manhattan, Kan.
March, 1949
CONTENTS
Preface v
Introduction 1
Association and Other Units „ 9
Directions for Exercises in Plant Ecology 13
Quadrat method 13
Types of quadrats 14
List quadrat 14
Exercise 1. List quadrats " 17
Count quadrat 17
Exercise 2. Count quadrats 18
Area list quadrat 19
Exercise 3. Area list quadrats 19
Basal area 20
Exercise 4- Basal area 22
Recording quadrats by photography 22
Exercise 5. Recording quadrats by photography 23
Pantograph charts 23
Exercise 6. Charting by pantograph 25
Area quadrats by squares 25
Exercise 7. Charting by squares 25
Additional charting 25
Point-observation quadrat 26
Exercise 8. Point-observation quadrats 27
Forest modification of the point-observation method ..... 27
Exercise 9. Forest modification of the point-observation
method 28
Permanent quadrats 28
Exercise 10. Permanent quadrats 29
Denuded quadrats 29
Exercise 11. Denuded quadrats 29
Clip quadrats 29
Exercise 12. Clip quadrats 30
Tree count 30
Simple tree count for frequency 30
xi
xii CONTENTS
Exercise 13. Tree count 30
Exercise 14- Tree count with diameter classes 31
Area tree counts or tree quadrats 32
Exercise 15. Area tree counts 33
Special-purpose tree counts 33
Tree count done by student classes 33
Exercise 16. Class tree counts 35
Other methods of determining frequency 35
The string method 35
Exercise 17. Determining frequency by the string method . 36
Line-interception method of sampling vegetation 36
Exercise 18. Line-interception method 38
The method of squares by use of a frame 39
Exercise 19. Frequency by the method of squares by use of
a frame 39
Percentage area frequency 40
Exercise 20. Percentage area frequency 40
Point-quadrat method 40
Exercise 21. Point-quadrat method of determining frequency 41
Community coefficient 41
Exercise 22. Frequency index community coefficients ... 42
Transects 43
Exercise 23. Line transect 44
Exercise 24. Belt transect 45
Exercise 25. Associational transects 45
Mapping 46
Types of maps 46
Exercise 26. Mapping or map making 59
Charting 59
To show overlapping ranges 62
Polygonal expression of data: polygraph 63
Exercise 27. Charting 64
Comparison of evaluation scales 64
Unequal scales for rating species in communities 65
Aquatic situation 66
Root systems of aquatic plants 68
Exercise 28. Root systems of aquatic plants 68
Depth of water in which aquatic plants are growing 69
Exercise 29. Depth of water 69
Physical features of the water 69
Exercise 30. Lake study 70
CONTENTS xiii
Exercise 31 . Stream study 70
Exercise 32^ Boglake study 70
Water constituents 71
Exercise 33. Water constituents 71
Character of the bottom 71
Exercise 34-. Bottom samples 71
Zonation 71
Exercise 35. Zonation 72
Alternation 72
Exercise 36. Alternation 73
Factors of habitat 73
Introductory to Factors 73
Temperature 73
Exercise 37. Heat measurements 75
Precipitation 76
Exercise 38. Precipitation 77
Relative humidity and vapor-pressure deficit 77
Exercise 39. Relative humidity and vapor-pressure deficit . . 78
Light 78
Exercise 40. Light 79
Wind 79
Exercise 41- Wind 79
Evaporation 80
Exercise 4-2. Evaporation 81
Dragoyle 82
Exercise 43. Dragoyle 83
Exercise 44- Climate 84
Soil 84
Hydrogen-ion concentration 84
Exercise 45- Determination of hydrogen-ion concentration, pH 87
Soil water content 87
Exercise 46. Soil water content 88
Mechanical analysis of soil 88
Exercise 47- Mechanical analysis of soil 89
Soil composition 89
Soil horizons (soil profile) 89
Exercise 4-8. Soil profile . . 91
Profile of the surface of the ground 91
Exercise 49. Surface profile 93
Peat study 93
Exercise 50. Peat 97
xiv CONTENTS
Characteristics of communities: a sociological summary .... 97
Quantitative analytic concepts 99
Abundance 99
Density 99
Dominance 99
Frequency 100
Qualitative analytic concepts ■ . . 100
Sociability 100
Vitality 101
Periodicity 101
Stratification 101
Synthetic concepts 102
Presence 102
Constance 102
Fidelity 102
Form concepts 104
Raunkiaer life-form classes 104
Exercise 51. Raunkiaer life-forms 104
Raunkiaer leaf-size classes 107
Exercise 52. Raunkiaer leaf-size classes 107
Genetic sociology 107
Dynamic behavior 107
Succession studies . . . 108
Initiating secondary successions 109
Fire 110
Exercise 53. Burning Ill
Influences of civilization Ill
Exercise 54- Influences of civilization 112
Plants as individuals: Autecology 112
Exercise 55. Individual plant study 113
Growth of trees in diameter 113
Exercise 56. Growth of trees in diameter 114
Annotated lists 114
Vegetation formula 116
Nomography 117
Reports 118
General outline for ecological work 118
Exercises on the structure and physiology of plants 121
Exercise 57. External anatomy 121
Exercise 58. Internal anatomy 123
Exercise 59. Physiology 125
CONTENTS xv
Soil characteristics 128
Soil descriptions 128
Exercise 60. Soil characteristics 130
Equipment for field exercises 132
Index 135
INTRODUCTION
Purpose
The purpose of this manual is to give directions for the under-
taking of beginning ecological work with the use of a minimum of
apparatus, particularly elaborate apparatus. The desirability of
ecological study to aid in the development of independent think-
ing, together with the encouragement of cooperative endeavor,
is recognized. Valuable training is given an inquiring mind
both in stating and in attempting to solve ecological problems.
Although the basic exercises are simple and serve to introduce the
subject, they can be extended to more detailed work, even to prob-
lems for actual research.
Certain experiments utilize instruments. The simpler instru-
ments here emphasized may later be replaced by more com-
plicated ones or by recording instruments as occasion arises.
Plant ecology basically is a study of plants in relation to their
environment. However, in evaluating the environment one must
either use words of quite general and often indefinite meaning or
take advantage of instrumental measurements. It is true enough
that directions for the use of instruments are relatively easy to
give. Their employment may, however, take up too much of the
time that can be allowed for work in the field. I believe the bal-
ance between the plant and the instrumental sides of an ecologi-
cal study should favor the plant side, wherever possible.
The experimental side of ecological work usually requires con-
siderable time. Beginning classes therefore can seldom perform
more than the simplest experiments. It may be possible for the
instructor to set up the experiment and carry it along while the
students make observations or read instruments at intervals dur-
ing its progress. However, many students feel that they are play-
ing an important part when they collect data for an experiment
which requires a number of years to complete.
2 FIELD MANUAL OF PLANT ECOLOGY
For ecological field work a knowledge of plants in every stage
of their development is of prime importance. Such complete
knowledge even in a given region is seldom secured. Conse-
quently, certain field exercises need to be preceded by the naming
of at least the more important species as they are pointed out,
or this can be done in the classroom with herbarium specimens
or pictures. The students should be provided with plant lists
upon which they may make annotations as the important plants
are pointed out to them. Unknown plants may be so designated
until identification is possible. If the names of the plants are not
known, collections should be made and numbered. Those num-
bers should be used when referring to the plants until their scien-
tific names have been ascertained. Some collecting equipment,
if only an old magazine or scrapbook in which to dry specimens,
is important. It is always well to preserve specimens, especially
of important or critical species, to permit subsequent checking of
identification.
Detailed directions for the collecting of plants to make a per-
manent herbarium are to be found in several recent books, of
which the following are among the best to consult :
Hitchcock, A. S., " Methods of Descriptive Systematic Bot-
any," Chap. 8, John Wiley & Sons, Inc., New York. 1925.
Pool, R. J., " Flowers and Flowering Plants," 2d ed., Chap.
27, McGraw-Hill Book Company, Inc., New York. 1941.
Swingle, D. B., "A Textbook of Systematic Botany/' 3d
ed., Chap. 3, McGraw-Hill Book Company, Inc., New York.
1946.
A simple serviceable press may be made by nailing and clinch-
ing together three pieces of lath, each 18 inches long, and seven
pieces, each 12 inches long, as a lattice for each side. Heavy
cords, each with a bowline loop in one end, tightened around the
press about one-fourth of the way from each end furnish the pres-
sure to flatten the plants in drying. The plants, bent as necessary,
are placed in folded sheets of newspaper. These in turn are placed
between driers (strong blotting paper) in the press. Driers are
taken out of the press, dried and replaced during the process of
drying. Sheets of corrugated boxboard may be interspersed in
the press to facilitate drying.
INTRODUCTION 3
In getting acquainted with the plants of a region, the various
botanical manuals should be employed. If one is not acquainted
with the proper manuals, a publication by S. F. Blake1 is an up-
to-date listing of those used in various areas of the United
States, including each of the individual states. An acquaint-
ance with plants at their various stages can be obtained only
by individual experience. Collections and their determination
are a great aid in this respect. The more plants one knows,
the easier it is to learn additional plants. Knowledge gained
in one region is more of an aid in another region than one
realizes.
Use of the Exercises
Nearly all the exercises given in this manual have at one time
or another been put into active use by the author at the Univer-
sity of Michigan Biological Station at Douglas Lake, Cheboygan
County, Michigan, and there have demonstrated their worth.
Minor modifications may sometimes be necessary to fit the exer-
cise into different regions. Getting acquainted with the vegeta-
tion of an area, the way it is built up, and the way it is related
to the environment are the major objectives of field ecologists.
Certain exercises, such as the quadrat method (or sample-plot
method), are of such fundamental importance that it is possible
to do a whole summer's work using no other method, especially
in areas where there are several plant associations or types or
communities of vegetation. If there are not many types of vege-
tation but several areas of the same type, a summer's work can
be used in bringing out the closeness of agreement between the
different areas.
The outcome of such study is an appreciation of what vege-
tation is and what factors enter into its development and spread.
The ability to reconstruct the history and to predict, often in
great detail, what will happen to vegetation of a given area in the
course of time, may also be developed.
1 Blake, S. F., and Alice C. Atwood, "Geographical guide to floras of the
world, Part I," U.S. Dept. Agr. Misc. Publ. 401. 1942. For the separate states
of United States only, a briefer but later annotated list is the following: Blake, S. F.,
"State floras of the United States," Chron. Bot.t 7: 258-261. December. 1942.
4 FIELD MANUAL OF PLANT ECOLOGY
Equipment
In this manual special effort is given to the setting up of exer-
cises that utilize a minimum of special equipment. Frequently
material may be present that can be set up on the spot. At such
time as finer, more elaborate equipment is available, better re-
sults can be expected. There is a tendency to overemphasize the
fineness of expression as against the variability of the original
data, as for instance, when one records 3.333 as a measurement
resulting from an estimate that a certain thing is 3 and about one-
third units in length. The significance of figures would allow for
no more than 3.3. Both instructor and student should appreci-
ate the difference between measurement and estimation and re-
alize that in this type of work excess of data tends to average out
inconsistencies which may creep into not-too-perfect original meas-
urements.
Student personal equipment includes a field notebook. Per-
haps the simplest is the aluminum cover which may be opened to
permit the insertion of ordinary notebooks of various sizes. A
cover about 4.5 by 7.5 inches (13.5 by 19 centimeters) in size is
in general the handiest. The fillers may be regular notebooks
bound at the top or loose leaves. Paper that will not go to pieces
and will not stick together upon getting wet is most desirable for
field work. Pencils depend upon the preference of the individ-
ual. The 1H or 2H pencils, which mark well without smudging
and do not run when wet, are the best. It is wise to have the
pencil tied to the notebook and the notebook provided with a
cord to hang from the student's neck.
Thin-lead, waterproof colored pencils are sometimes valuable
but are not usually recommended for use in the field.
A ruler may be etched on the cover or one may cement a nar-
row strip of cross-ruled paper to the inside of the cover. A rubber
band around one cover under which to insert the sheets which have
been written upon is likewise handy.
A knapsack to carry the various items of equipment is de-
sirable, particular^ on daylong trips. A good type is a shell
bag such as is used by hunters. A trowel for digging and a hunt-
ing knife are often indispensable. For quadrat work, metersticks
INTRODUCTION 5
of some form are essential. A pair hinged to open at a 90-degree
angle are often advantageous. A hand lens is also useful.
Compasses
In the field a magnetic compass is almost a necessity. Keep-
ing directions well when one is simply coursing through an area
is comparatively easy, but when one is continually stopping, turn-
ing around, and taking notes, especially in woods, it is usually
impossible to maintain direction without reference to a magnetic
compass. In use, hold the compass well away from any metal
that would affect the needle.
Note: A watch which is running within 15 minutes of correct
standard time, not daylight-saving time, may be used in sun-
shine as a compass with reasonable accuracy by holding the watch
immediately in front of you with the hour hand pointing toward
the sun. Halfway between that and 12 on the watch is due south
in the Northern Hemisphere. At night knowledge of some of the
stars may be advantageous; certainly any ecological worker in
the Northern Hemisphere should be acquainted with the location
of the polestar at the end of the Little Dipper. The two outer
stars in the bowl of the Big Dipper point toward the North Pole.
This is usually the easiest method of locating the polestar. It
may be well to mention that the angle of declination of the pole-
star with the horizon is the latitude of the place of observation.
The magnetic deviation of the compass in a given region may be
obtained from navigation charts or other maps.
Forms
Forms for the recording of data are very useful. However,
avoid sacrificing individual development of students by having
too many forms prepared in advance to fill out. Setting up suit-
able forms is part of the student's work. It can readily be chan-
neled to a suitable type and the form mimeographed and made
available at the proper time.
Cross-ruled Paper
For the ordinary notebook, a few pages of cross-ruled paper
are often distinctly advantageous in sketch mapping or drawing
6 FIELD MANUAL OF PLANT ECOLOGY
parts of plants to scale. Remember that water will wash out the
blue lines of blue-lined cross-ruled paper.
Maps
Maps are an important part of a student's equipment. If
base maps of the local area are not available, the class can make
such maps as a part of their course (see Exercise 26).
Miscellaneous Suggestions for Comfort in the Field
Clothing. While the subject of clothing is largely a personal
matter, in some types of ecological work it is important that the
clothing be of material which will withstand field conditions and
suitable for the climate. Clothing as well as shoes should be of
the sort that will dry out quickly after a soaking.
Sunburn. A coat of tan, acquired early, preferably before
summer, will aid greatly in preventing undue sunburns. A day's
work on sand dunes or in and out of water too often results in se-
vere cases of sunburn. Dark glasses aid in protecting the eyes.
Under severe conditions the use of creams on the face and espe-
cially the lips, as a protection, may be desirable.
Poison Ivy. If poisonous species of Rhus [R. vernix, poison
sumac, and R. radicans (R. toxicodendron), poison ivy or " poison
oak," as it may be called] are present it may be desirable to have
a cake of strong laundry soap to wash with after contact with the
poisonous Rhus. For long trips, calamine lotion to sooth and
potassium permanganate crystals to make about a 10 per cent
solution to oxidize the resin or a 5 to 10 per cent aqueous ferric
chloride solution to counteract the resin may be included.
Small Items. Various small items of equipment suggest them-
selves, such as pocketknives, extra handkerchiefs, and extra pen-
cils. The leader might well have a small sewing kit, with extra
safety pins and a Red Cross first-aid kit. Salt tablets to counter-
balance the loss of salt through the skin in hot weather should
be added to the medicine kit.
Insect Repellents. Field trips in parts of the country are made
most unpleasant by pests, of which mosquitoes, chiggers, black
flies, deer flies, nosee-ums, and stable flies are perhaps the most
common. There are several repellents on the market, but those
INTRODUCTION 7
that are best and may be used in the smallest quantity contain
pyrethrum extract. Citronella or pennyroyal in olive oil is com-
monly used but is not so effective as oils containing pyrethrum.
A preparation sold under the trade name d-Ter is a moderately
effective insect repellent. Insect Repellent 612 was successfully
used in the tropics during the past war. Tars also are good re-
pellents but have the disadvantage of staining garments. Sprays
from flit guns may be useful in camp. Most sprays are a form of
mineral oil, or some light oil. If the spray oil is fortified with py-
rethrum extract or some other good repellent, it is most effective.
The Pyre thrum-aerosol Bomb, recently developed, is more effec-
tive than sprays and considerably more convenient to carry and
use. Wearing extra clothing may sometimes be necessary to repel
pests. Mosquito nets and heavy gloves are essential in some areas
at certain times of the year. If mosquitoes are not too abundant
I have found that if one remains quiet in the place where he wishes
to take notes and kills the mosquitoes that come to him within
the first 3 or 4 minutes, usually he can then be free to take notes
for about 5 or 10 minutes. Any movement which disturbs the
vegetation, however, brings more mosquitoes.
Bee Stings. If the stingers of bees are pulled out the reverse
of the way they went in, the discomfort will generally be but tem-
porary. If a little soda is available it will neutralize the formic
acid. Wet clay mud is also effective.
Poisonous Snakes. In areas in which poisonous snakes
abound it may be necessary to have an antivenom kit along and
to know how to use it.
Photography. Certain types of ecological work depend upon
general impressions as well as accurate observations in the field.
Sketches may serve the purpose, but as a rule a picture taken
with a camera may be as effective and is much quicker. Since
most students are familiar with the use of a camera only a few
special pointers for ecological work need be given here. The type
of camera will depend upon individual preference, but in choosing
a camera consideration should be given to size, weight (especially
as an extra), ease of getting films, and utility of size in making
lantern slides or for reproduction. In photographing vegetation,
the exposure necessary is longer than in taking pictures of street
8 FIELD MANUAL OF PLANT ECOLOGY
scenes. In photographing vegetation one seeks details, so he
should take every advantage of opportunity to stop down as far
as practicable and utilize a correspondingly greater amount of
time for the exposure. When taking pictures of grassland, the
best pictures are taken against the sun, but one must shade the
lens so that the sun does not shine directly on it. For pictures in-
side of forests, the very best time is the early morning just before
the sun has appeared above the horizon. For such photographs
the layout is best determined the previous day. The early diffuse
light penetrates beneath the canopy without causing shadows.
Such conditions are very suitable for showing the general forest
vegetation near the ground. Proper stopping and length of time,
of course, need to be given. This can be learned by experience
or obtained through the use of exposure meters. The resulting
picture will be a great improvement upon pictures taken in the
sunshine because of the lack of snowlike leaves which have re-
flected too much light into the camera and the dark jet spaces
in which insufficient details can be recognized. Photographs may
also be made of individual plants, both in situ and after they have
been picked or dug and arranged. One of the most suitable back-
grounds for many such plants is the tar-paper roofing which is
often found in summer camps. Very white paper or cloth is ob-
jectionable, but often used, nevertheless. The jet-black back-
ground is often disadvantageous in reproducing the pictures by
means of the photoengraving process. Plenty of light should
reach the plant from various angles, so that no shadow will be
visible. In general, for showing details of the parts a sketch or
drawing is better than a photograph, but for showing masses of
plants in the field, the photograph is much simpler. Photographs
made at different intervals at the same place record data very
quickly. If good notes have been taken in the first place so that
a class in a later year may use them and take their own up-to-date
pictures, good ecological comparisons may be made.
ASSOCIATION AND OTHER UNITS1
For an ecological study of vegetation, a certain amount of
nomenclature is necessary. The fundamental unit is variously
cjlled -plant association, plant community, or plant type. Standard
definitions of these are as follows : An association may be defined
as a relatively^ uniform area of vegetation in which the interrela-
tionships of the component plants permit them to endure the
physical environment. Or, according to Nichols: "Viewed in the
concrete, a pjant association may be dfifinedLaa a plant community
characterized by its essentially homogeneous physiognomy and
ecological structure and by its essentially homogeneous floristic
composition, at least with regard to dominant species. Viewed
in the abstract, the association may be defined as a vegetation-
uniL characterized by an essentially constant floristic composi-
tion^ at least with regard to dominant species. "
Plant community is to be defined much the same except that
occasionally a geographic boundary is assigned, which means that
it might contain more or less than one association.
Plant type, used particularly by foresters, may express the
equivalent of the association, or it may be a part of an associa-
tion dominated by different groupings of dominant species.
The association, by one name or another, has been used for a
long time as a satisfactory unit, but recently efforts have been
made to limjtjts use to the final unit, the so-called climatic climax,
and to use associes for the temporary or serai units leading up to
it. This needlessly complicates a subject already burdened with
terminology.
Formations. This term, formerly used much more than now,
includes groups of associations which are characterized by having
dominant species of essentially the same growth forrn.
*Cf. also Weaver, John E., and F. E. Clements, "Plant Ecology," 2d ed.,
pp. 89-105 in part, McGraw-Hill Book Company, Inc., New York. 1938; Braun-
Blanquet, J., "Plant Sociology" (translated and revised by G. D. Fuller and
H. S. Conard), pp. 21-25, McGraw-Hill Book Company, Inc., New York. 1932.
9
10 FIELD MANUAL OF PLANT ECOLOGY
Provinces. The various assQfiia.tio.iis_ and formations of a
country may be assembled into provinces which are set off from
one_anQther by differences in environmental factors and plants.
For instance, the deficient rainfall of the winter season combined
with ample summer rainfall favoring grasses are the outstanding
characteristics of the prairie province. The principal factors in
the delimitation of provinces are the average temperatures
through the year, the amount and distribution of rainfall, and in
some cases the topography of the country and the plant covering.
The climate, the soil, and the plant covering are interrelated quite
closely.
Considering United States broadly, the following major prov-
inces may be recognized: The Prairie Province in the center of
the country is replaced to the eastward by forest provinces. In
the northeast there is the Northeastern Coniferous Forest Prov-
ince, with the eastern white pine, Pinus strobus, as one of its out-
standing species. South from it is the extensive Central Decid-
uous Forest Province, with the sugar maple, Acer saccharum, as
an outstanding species. Next comes the Southeastern Coniferous
Forest Province, with the loblolly pine, Pinus taeda, as one of the
outstanding species, followed in the southern part of the Florida
peninsula and in the region of Brownsville, Texas, by the Sub-
tropical Province. The region of Key West, Florida, is the only
portion of the United States vegetated by a part of the Tropical
Province.
In the eastern part of the Prairie Province one of the dominat-
ing grasses is the big bluestem, Andropogon furcatus, while in the
western part the buffalograss, Buchloe dactyloides, is supreme.
West of the prairie is the Rocky Mountain Forest Province,
which splits into two forks in northern United States. The east-
ern fork retains the name Rocky Mountain Province. The pon-
der osa or western yellow pine, Pinus ponder osa, is one of its
outstanding species. The western fork going down the moun-
tains in the Pacific Coast states is called the Pacific Coast
Province. The sugar pine, Pinus lambertiana, is one of its im-
portant species.
Between these two mountain provinces lie two dry land areas.
The northern portion, characterized by the sagebrush, Artemisia
ASSOCIATION AND OTHER UNITS 11
tridentata, is spoken of as the Basin Province, while the southern
part, extending down into Mexico, characterized by many types
of cacti, is named the Sonoran Province.
Subdivisions of these provinces are recognized locally. It is
most probable, however, that a beginning ecology class would
not be working in vegetation belonging to more than one, at most
two, provinces during a summer.
Within each province, unless the area is covered by the cli-
max association, one finds series (seres) of associations, related
siiccessionally, leading towards the climax. To have succession1
requires migration, in other words, the spread of the plants that
are to bring about succession, together with their ecesis or es-
tablishment. If ecesis does not follow migration, succession can-
not take place. When the succession reaches the stage in which
under present natural conditions no other association will fol-
low, that association is spoken of as the climax association. This
really does not mean that it will last forever, for climatic changes
do take place ; however, so slowly that they are not discernible in
a human lifetime. In addition, it does not mean that the climax
association will come to occupy each spot. Many things pre-
vent the tendency's finding full expression. In some cases asso-
ciations filter into others, producing mixtures of greater or less
extent. The term mictium is used. Theborder line between one
association and another is spoken of as an ecotone. The character-
istics of ecotones show up most sharply between forest and grass-
land associations.
Recognition of plant associations or plant communities. Only
experience enables one to recognize plant associations and thus be
able to tell whether a particular grouping should be spoken of as
an association or a part of an association. In case of doubt,
the various exercises indicated can be conducted and from the re-
sults a decision arrived at. For the person without experience
there is a good deal of trial and error involved, but this need never
interfere with taking up a definite area and conducting quadrat
and tree counts on it. Once the idea is mastered, there is usually
little difficulty in carrying on further work. In working with as-
1 Cf. Weaver and Clements, op. cit., Chaps. V-VII; Braun-Blanquet, op. cit.
(tr. and rev. by Fuller and Conard), parts of Chap. XIII.
12 FIELD MANUAL OF PLANT ECOLOGY
sociations the determination of the dominant species is the first
consideration (see Exercises 1, 2, and 13). All other species may
be considered as secondary. Among the secondary species, how-
ever, some may be found which are dominant in other associa-
tions. Their position in a given area may then indicate invasion
or they may be relics of the association previously occupying the
ground. This gives four classes of species : dominant, secondary,
invading, and relic. A fifth category includes species which oc-
cur in a wide variety of habitats and have so little to do with
characterizing any that they are usually grouped by themselves
as ubiquitous species. Several associations have more than one
dominant species. If, in a given example, but a single dominant
species is present, that example is considered a consocies, e.g., the
maple consocies of the maple-beech association. Associations also
can be subdivided by the different appearance of parts, as tree,
shrub, and ground layers in a forest or according to different as-
pects at different seasons of the year. Such groupings have been
termed synusia, i.e., a natural grouping of species of the same
life form and with uniform ecological requirements.
More advanced students will find in the literature many addi-
tional terms used by various authors.
DIRECTIONS FOR EXERCISES IN PLANT
ECOLOGY
QUADRAT METHOD1
Before starting work on the quadrat method, be sure to study
over the section above entitled: Association and Other Units.
Also, either previous to undertaking the first set of quadrat counts
or shortly after taking the first set, study the exercise on life forms
(Exercise 51).
The quadrat method, known also as the sample-plot method,
i&J^basic method for many types of ecological investigation . It
received the name " quadrat method'7 from the squares used as
sample plots by F. E. Clements in 1898. The name " sample
plot" is, however, the name used more commonly by agronomists
and other workers, in both the plant and animal fields as well as
in other types of statistical work.
The basic principle underlying the method is the saving of
time and labor by selecting, in accordance with a prearranged
plan, sufficient sample. plots or quadrats to give data which will
depart in no significant way from the. data that would have been
obtained if the complete area had been studied. The determi-
nation of the best size and the best number of sample plots is an
exercise in itself but will need to be made for each type of work.
In general classwork it is wiser to use three or four times the mini-
mum number in order to smooth out irregularities due to the in-
experience of students.
The quadrat, as usually used by ecologists, is a square area
one meter on a side. As used by American foresters the quadrat
is 6.6 by 6.6 feet, or Kooo acre. Originally a square, as now used
the shape may be quite variable; e.g., in plant-disease survey work
a circular hoop is employed. The size may vary from a square
10 centimeters on each side for moss and lichen studies to areas
1 Cf. also Weaver and Clements, op. cit., pp. 10-33.
13
14 FIELD MANUAL OF PLANT ECOLOGY
which may be 50 or more meters along the side in forest studies.
Whatever the size or shape, the basic principle remains the same,
viz., to acquire pertinent data from small plots which are to rep-
resent the area as a whole.
Many students in working for the first time with the quadrat
method feel that they are missing plants, especially conspicuous
plants. Yet if such plants are important ecologically, other mem-
bers of the class will find them in their quadrats. For such stu-
dents it is often worth while to go back and forth over the area
to try to find plants which have been missed in the quadrats. In
work in the aspen association in northern Michigan, where from
30 to 50 kinds of plants are found in an area, species are rarely
missed by a class taking 100 quadrats in the area. If one or two
are missed, detailed study brings out that only one or two, or
very few, specimens are present.
TYPES OF QUADRATS
Among the types of quadrats that may be used, the list quad-
rat stands foremost for ease in taking and for utility in introduc-
ing the subject.
LIST QUADRAT
Procedure. If a single individual is to take a series of list
quadrats, it may be advantageous to run a string through the
area to enable him to maintain a definite line or pattern. The
line may form any pattern, such as an N shape or M shape, or
simple straight line. If a class is to take list quadrats, they may
be lined up along one side of the area at intervals that will vary
with the size of the area. While single individuals may take a list
quadrat, it is much more economical to have pairs of students do
the work, one particularly to spot the plants, the other to record
and maintain the direction. If it is essential that high mathe-
matical accuracy be attained, the area should be laid off first,
with the lines of travel accurately determined.
In starting a series in from a road, it is well to step in 2 to 3
meters from the edge, whether it is a grassland or forest area, to
minimize or eliminate any effect that roads or trails may have.
In northern Michigan studies have shown that the effect of a road
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 15
is reduced to less than 1 per cent within 3 meters from the
road.
In setting up a list quadrat, stakes, surveyor's pins, or any con-
venient markers may be set at the four corners. In more impor-
tant work it is advantageous to have two metersticks on rods
hinged at the end with a strap to prevent their being opened
more than 90 degrees. Three corners having been located, the
rods may be turned 180 degrees and the fourth corner marked.
During this setting up, the students should keep off the area to
be studied.
Thejist quadrat, as its name implies, is a list of the names of
the, species present in the quadrat. It should include each and
every species, whether the name is known or not. In the list
quadrat, whether there are many or few examples of the same spe-
cies makes no difference, a^species is listed but once. The recorder
keeps track of the species and of course helps in ferreting them
out. When the plants in a quadrat are listed, the pair will pro-
ceed forward the stated distance, set up the next quadrat, and
repeat the process. The simplest and most satisfactory form in
which the data may be recorded is as follows:
Species
Quadrat number
Total quadrats
Plant A
1—3—9
1—2—3—4—6—9—10
2—6—8—10
(3)
Plant B
(7)
Plant C
(4)
Summing up the data is then simpler than if completely sepa-
rate lists are made of each quadrat. If a good many species are
found in the area, there are advantages in having the list made
alphabetical. The number which is put after the species is the
number of the quadrat taken. Any additional numbers separated
from those ahead by a hyphen mean that species A was found in,
say, the first, third, and ninth quadrats, etc. This makes it pos-
sible to separate the data by quadrats if that is necessary and it
avoids the uncertainty that marks or crosses always engender.
For instance, have you credited quadrat 3 with such and such a
species? The number 3 would settle the question; an X might not.
When the work is completed the number of quadrats in which each
16 FIELD MANUAL OF PLANT ECOLOGY
species occurs will be written after the name of the specie^. This
makes the determination of frequency a simple matter, since fre-
quency is per cent. The frequency index where a species occurs
in 10 out of 10 quadrats is 100; in 50 out of 100 quadrats, 50.
It is seldom desirable to determine frequency closer than to whole
per cents. Comparing the frequencies of plants in different areas
is an important part of certain types of ecological work.
If the name of the species is not known, sufficient material
should be put in a magazine or scrapbook and labeled the same
as on the field notes (e.g., " Unknown No. 1"). If identification
cannot be made in the field, the plant should be carried on the
records as unknown 1, 2, 3, etc. Thus it is possible to carry on
list quadrat work without knowing the name of any of the plants
by simply giving them some designation and preparing speci-
mens which will permit identification by some authority later.
Assembling the Data. If a single individual is taking list
quadrats, he has merely to count up the number of quadrats and
express that number as the per cent of the whole number of quad-
rats taken. If, however, a class has taken the quadrats, the sim-
plest procedure is to call the name of a plant, following which each
group in turn adds on the number of quadrats in which they have
found it; the final figure being the total number of quadrats in
which the whole class found the plant, which is then expressed as
the per cent of the total number of quadrats taken. If 100 quad-
rats are taken regularly, this simplifies the expression of frequency.
The species in a list-quadrat frequency count may be arranged
in any order suitable for the purpose of the work. Common ar-
rangements are systematic order by families, alphabetically, or
by. life forms.
Accompanying a set of list quadrats there should be notes re-
garding the ^general lay of the land, type of soil, slope, and various
other features.
Before taking quadrats, one must consider the type of vege-
tation. In a forest the.size of the quadrats for the tree count must
he much larger than the size of the quadrats necessary for ade-
quate expression of the frequency of ground plants. It is there-
fore convenient to divide the plants into " trees" and "ground
plants" and use a different method for each. In general, trees
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY
17
may be considered as woody plants 1 meter or more in height.
The procedure with the trees will be explained later. However,
if a, tree occurs in a quadrat, list it with the ground plants. Woody
plants under a meter in height are counted as ground species, as
are the herbaceous plants. If special attention is to be given to
tfre reproduction of trees, the tree species are listed in accordance
with size or age. For instance, 1- or 2-year seedlings and small
saplings approaching a meter in height can be recorded as sepa-
rate units. For complete species frequency, however, these units
must be added together.
Exercise 1. List Quadrats
Take 10 list quadrats according to the pattern in the area des-
ignated, after reading over the material above. The following
form may be used in recording the data :
List Quadrat
Group No
Location
Date
Species
Quadrat number
Total quadrats
Frequency index
Plant A
1—2—5—7—8—10
1—3—4—5—6—7—9
2—3—4—5
3—4—5—6—7—8—9
6
(6)
(7)
(4)
(7)
(1)
60
Plant B
70
Plant C
40
Plant D
70
Plants
10
Be sure to accompany each table with data concerning the loca-
tion and characteristics of the particular set.
Note: This exercise will be repeated many times in different
parts of the same association and in different associations in the
areas studied.
Count Quadrat1
To supplement frequency determination with a knowledge of
the-jaumber of individuals of different species, count quadrats are
takenL The procedure is to complete the list quadrat for each
quadrat, following it immediately by the counting of the num-
ber of individual plants of each species. In recording it is con-
1 Cf. also Weaver and Clements, op. cit.} p. 13, as list or census quadrat.
18 FIELD MANUAL OF PLANT ECOLOGY
venient to use the number of the quadrat, the same as previously
indicated in the list quadrat, and below or after the list number
put in parentheses the number of individual plants, as shown be-
low. The summation of the data is the same as in the list quad-
rat, yielding in each case thfi._na.me of the plant, the number of
quadrats in which it is found, followed by, in parentheses, the
total number of individuals of that species found in the set.
The main difficulty in making count quadrats comes from the
fact that several plants appear separate above ground but are
really parts of a crown or rhizome system beneath the surface of
the ground. While from one standpoint these could be counted
as one plant, nevertheless, as the ecological action of the shoots
above ground is that of individual plants, it is more satisfactory
to count each shoot as an individual. An annotated list should
make this point clear if the data are to be used for other purposes.
The count quadrats call attention to the abundance, but still no
distinction is made between fine plants and coarse plants, which
simply indicates that the count quadrat is added information but
not complete information. While it is possible to evaluate an
approximation of cubic contents of the plant to use instead of
simply presence, the labor involved is such that it is seldom done.
The second difficulty is in the evaluation of a clump. Although
individual stems may be obviously a single plant, if the branching
is just above the ground, the individual shoots may in reality act
as individual plants. Whether to count the clump as one or to
count the individual shoots as one each must be decided on the
merits of the situation and the same system followed in the same
piece of work and in studies with which comparisons are to be made.
Stump sprouts present similar difficulty. Obviously they are
a single plant, yet by a more complete rotting of the stump the
sprouts may become separated as individuals. Possibly a good
method is to count only the thicker ones, i.e., those whose crowns
give them the chance to suppress the others by cutting off their
light.
Exercise 2. Count Quadrats
On the areas designated, first take a list quadrat in the usual
manner, recording the number of the quadrat in the set. Then
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY
19
count the plants of each species and put the number in parenthe-
ses under the quadrat number, as shown below. Continue until
all the quadrats are listed and counted. Use the following form
to tabulate data:
Count Quadrat
Group No.
Location . .
Date.
Species
Quadrat number
(individual plants)
Total quadrats
(total individuals)
Plant A
1 2 5 7 8 10
(4) (15) (1) (2) (10) (3)
13 4 5 6 7 9
(2) (6) (8) (15) (1) (4) (4)
2 3 4 5
(1) (2) (4) (1)
3 4 5 6 7 8 9
(25) (10) (2) (20) (13) (14) (5)
6
(9)
6
Plant B
(35)
7
Plant C
(39)
4
Plant D
(8)
7
Plants
(89)
6
(9)
Note: Repeat as directed.
AREA LIST QUADRAT
Occasionally, especially in some agronomic work, it is desirable
to know the area of the ground covered by each and every species.
In such cases the area may be measured by setting up cross strings
and counting the number of squares and major fractions occupied
by the species in question. In areas of low vegetation the use of
previously constructed frames with cross strings or wires will ex-
pedite the work in the field. Cardboard or celluloid squares of
different sizes will aid in doing this charting.
Exercise 3. Area List Quadrats
Set up surveyor's pins 10 centimeters apart on each side of the
square designated and connect with strings to form a checker-
board or place a frame with cross strings over the vegetation.
For each plant count the number of squares and major fractions,
as shown below, and record. Plants which occupy less than half
20
FIELD MANUAL OF PLANT ECOLOGY
a square may be indicated together as less than 0.5 or recorded as
shown in the diagram below (Fig. 1).
BASAL AREA1
Looking down at a quadrat, one often gets the impression that
the ground is rather thoroughly covered ; however, if clipped at the
A
C
OD
| B / \
(9
Fig. 1. A portion of a meter quadrat, the grid lines 10 centimeters apart, showing
how to count the squares to obtain the approximate area. The units are 10-centi-
meter squares. A is recorded as 2 units; B, 0.4 unit; C, 7 units; D, 0.01 unit; and
E, 1 unit.
ground level, it is seen at once that the plants emerging from
the soil occupy but a small amount of the area. Determining
the average area of the cross section of 50 or 100 or more stems
of a species at the ground level and multiplying by the average
number of stems of that species per square meter will give the
basal area for that species. Figures for each species added to-
gether give the total basal area.
There are two principal methods employed: direct measure-
ment of diameters within a measured area, or charting and meas-
uring areas on the charts. In the first method, direct measure-
1 Cf. also Weaver and Clements, op. cit., pp. 14-18.
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 21
merit may be made with a ruler graduated to millimeters or
sixteenths of an inch. Better still, use calipers, small ones for the
ground plants and tree calipers for trees. For cylindrical stems
one measurement of diameter is ample, but, if not cylindrical,
two or more measurements must be taken and averaged. With a
knowledge of the average diameter the average area per stem may
be calculated (irr2, that is, 3.14 times the square of the radius) and
this multiplied by the average number of stems in a unit area
will give the basal area.
Plants in clumps present a problem. Should each stem be
counted as an individual or should the whole clump be taken as
one? Normally the area of the ground covered by a rosette, a
bunch, or a hummock is measured from edge to edge, which does
not settle whether the bunch is one or several plants. For such
plants as Festuca odoflora, which grow individually in tight mas-
ses, the problem is very definite and different from a case such as
Car ex leptalea, where a clump 8 to 10 centimeters in diameter may
have in it only a relatively small number of culms projecting into
the air.
The data should include: the area of ground to be measured,
the number of stems per unit of area, and the average area per
stem. From these figures the percentage of ground occupied by
the plants may be calculated.
In the second method it is necessary to chart, in detail, the
stems and clumps at ground level in the area selected. Such
charting is most conveniently done on cross-ruled paper after the
area has been laid out in squares of convenient size (e.g., 10-centi-
meter squares) with surveyor's pins and string. Charting may
be done by penciling in the outlines of the various stems and
clumps on the cross-ruled paper or by using a pantograph, if
conditions permit the full sweep of the pantograph arms. Still
another way is to photograph the area from directly overhead.
From any such charts the actual area is determined by counting
the number of small squares occupied by the stems or clumps,
ignoring fractions of squares, if less than half a square is covered,
and counting as full squares whenever more than half a square is
covered. A planimeter may be used to trace around the outlines.
When suitably calibrated, a direct reading of area is made. Still
22 FIELD MANUAL OF PLANT ECOLOGY
another way is to cut out the outlines, as they have been drawn
on paper, and weigh them on a delicate balance. Knowing the
weight of a definite area of the same kind of paper permits making
a calculation of the area occupied by the stems and clumps, in
other words, the basal area.
The student will undoubtedly be impressed with the really
small area of ground surface occupied by plants in what appears
to be dense vegetation. This varies markedly from association
to association in succession and may sometimes be used as an
early indication that succession is under way. Determinations
made in succeeding years may show unexpected changes in the
density of the vegetation, even in the same area. (See page 237
in F. C. Gates, "The bogs of northern Lower Michigan," Ecol.
Monog., 12:213-254. 1942.)
Exercise 4. Basal Area
Lay out a quadrat and count the individual plants in it by
species. With small calipers measure the diameter of 100 or more
stems of each species in the quadrat at the ground and average
by species. Find the area by the formula wr2. If the stems are
not circular in cross section measure sufficient diameters of each
stem to give the diameter of an equivalent circle and proceed as
above. Divide the area covered by the plants by the total area
of the quadrat to obtain the percentage of ground occupied by
plants, i.e., the basal area.
Repeat, both in similar and in different habitats, using any
of the methods mentioned above.
RECORDING QUADRATS BY PHOTOGRAPHY1
One of the quickest ways to record the appearance of an area
is to take a photograph of it. Cameras may be set up directly
above the center of the quadrat high enough to make it fill the
film. A 6-foot folding stepladder may be used to support the
camera as illustrated in Fig. 21 of Weaver and Clements. At
the same time it is often wise to take at least one side view of the
quadrat to help in the identification of the plants. If pictures
and counting are done, the photograph should be taken immedi-
1 Cf. also Weaver and Clements, op. cit., pp. 30-31.
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 23
ately after the quadrat is staked out and before disturbing the
vegetation. Recognition of individual species of plants which
closely resemble one another is likely to be impossible from photo-
graphs. However, for recording general appearance there is no
better method.
Exercise 5. Recording Quadrats by Photography
Arrange a camera directly overhead and high enough from
the ground to include all four corners of a quadrat. If shadows
are objectionable, do this work in the shade, if possible, or on a
cloudy day.
Supplement the overhead picture with exposures from one or
more sides taken at an angle of 30 to 45 degrees with the ground.
PANTOGRAPH CHARTS1
If an area includes only low plants, as in the shortgrass plains,
it is possible to set up a pantograph in the field and chart directly
to scale the areas occupied by individual plants and clumps. The
amount of reduction varies according to the set of the instrument.
The pantograph is fastened near a corner of a drawing board
which is set up next to the area to be charted in such a way that
the encircling of plants by the pointer arm yields a similar, but
smaller, penciled shape on the chart affixed to the drawing board
in the proper position (Fig. 2). The usual 22-inch pantograph
available in bookstores will reduce an area 50 by 50 centimeters
to }i that size conveniently. For research work larger sizes are
desirable.
When all the plants in the area have been gone over, the field
work is complete. The accuracy of the method makes statistical
analysis possible and charts made at one time may be com-
pared with subsequent charts of the same area, if the area is per-
manently marked.
The method requires somewhat cumbersome apparatus, good
selection of area, and considerable time and close attention, so
that but one or two may be done in a day. If there are plants
sufficiently higher than the pantograph arm to interfere with its
free movement, a pantograph cannot be used. For basal area
1 Cf. Weaver and Clements, op. cit., pp. 24-26.
Drawing Board with Chart
Area to be Mapped
•; • * fp^
Fig. 2. {Above) A pantograph set to reduce to %. To the left is a drawing board
on pegs, firmly set up the proper distance from the area to be charted. On it is
fastened the pivot A of the pantograph and the drawing paper. At B is the lead
which marks on the chart; at C the pointer, now at the lower left corner of the area
24
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 25
work, especially after clipping, the pantograph can be used to
good advantage.
The names of the plants drawn must be appended as soon as
drawn. Conventional signs may be selected to represent certain
of the commoner species. As always, north should be indicated.
Exercise 6. Charting by Pantograph
If opportunity presents, chart one or more quadrats by means
of a pantograph set to reduce to }i, or other suitable reduction.
AREA QUADRATS BY SQUARES1
If a pantograph cannot be used, the area may be staked out
in convenient units and strings run each way through the vege-
tation to form squares. Then the observer charts on cross-ruled
paper as nearly as possible the extent and kinds of plants, square
by square.
Exercise 7. Charting by Squares
Stake out an area with surveyor's pins and run strings through
the vegetation to form 10-centimeter squares. Chart on cross-ruled
paper each square in turn, using convenient conventional desig-
nations for the plants. Note: the first letter of the genus im-
mediately followed by the first letter of the species is usually the
simplest symbol to use. In studies in the prairie "Af" stands
for Andropogon furcalus and "As" for Andropogon scoparius.
Extra letters must be added to avoid confusion, however. For
example, in northern bog studies "CI" may stand for Carex lasio-
carpa, but "Calc" for Calamagrostis canadensis and "Cali" for
Calamagrostis inexpansa.
Repeat with other areas as often as desired.
ADDITIONAL CHARTING
Many different purposes may be envisioned for the use of chart-
ing procedure; e.g., the area of a single type of species, or the loca-
tion of seeds that are observed falling on an area; occurrence of
seedlings, location of mosses, lichens, or plants of a certain color,
or diseased plants, and other problems.
1 Cf. also Weaver and Clements, op. cit., pp. 23-24.
to be charted. Some support may be needed at D, the slider, to hold it off the ground
and yet permit free movement as the pointer traces the outlines of the plants in the
area being mapped. (Below) Making a pantograph chart on the college pasture at
Hays, Kansas. (Courtesy of F. W. Albertson.)
26 FIELD MANUAL OF PLANT ECOLOGY
POINT-OBSERVATION QUADRAT
For quick determination of the plant coverage of areas in
connection with agronomic studies, particularly grazing, the
point-observation method was developed by George Stewart
and S. S. Hutchings (Amer. Soc. Agron. Jour., 28:714-722.
1936). While the method was developed in grassland areas,
with certain modifications, as indicated later, it may also be used
in forested areas. The materials used consist of nine surveyor's
pins conspicuously colored, a ruler or string, and squares of card-
board or celluloid, 10 centimeters on a side. In this method the
center pin is inserted a short distance into the ground at the
first station and the eight pins are set along 45-degree angles,
forming an octagon, which for practical purposes is essentially a
circle. The radii may be varied but a radius of 0.565 meter yields
a circular area of 1 square meter, or a radius of 0.80 meter yields
an area of 2 square meters. The same setup is made at each sub-
sequent station, the centers of which are located in accordance
with a prearranged plan. In each area the plants should be noted
first, or, as is commonly done, the plants are grouped in certain
predetermined categories, depending upon the subject of the
work. In grazing studies, the plants grazed may be divided into
grazing grasses, palatable nongrasses, and weeds. In ecological
work in northern Michigan we have arranged the groupings as
follows : specially important species by themselves, the composites,
other forbs, the grasses, the sedges — or the grasses and sedges —
the mosses, and the lichens. When desired, additional categories
are set up, such as seedlings of dominant species or of invading
species.
Individual species may be used as well as groups of species,
but the particular advantage of the method is that the less im-
portant species may be grouped so as to use less time in obtaining
the data on the area. In actual operation, after the classification
is set up, the observer uses the square cardboard by holding it
over the vegetation and counting the number of times that that
area will cover each category of the classification. The results
are then expressed as units and tenths. When the data are as-
sembled, division of the sums by the total area will express the
coverage per square meter.
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 27
If a radius of 0.565 or 0.800 meter is used, then division by
1 square meter or 2 square meters, respectively, yields the cover-
age per square meter. For grassland areas this yields coverage
which may then be compared to basal area to determine how much
spreading has taken place. For instance, the basal area at the
ground of Festuca octoflora and one plant of Buchloe dactyloides
may be the same, but the amount of coverage of the buffalo-
grass plant is much greater than that of the Festuca,
Exercise 8. Point-observation Quadrats
Set up a point-observation quadrat by putting in a center pin
and eight pins, each 80 centimeters from the center on radii 45
degrees apart. Select suitable categories of plants. Taking each
category in turn, using the square cardboard (10 centimeters on
a side) hold the card over the vegetation, counting the number
of times the area of the card will go into the area of that category
of vegetation and record. To check the visual record, clip off the
plants of one category and gently hunch them together on the
card. It takes a little practice to make duplicate observations
check. Divide results by 2 to obtain the coverage per square
meter.
FOREST MODIFICATION OF THE POINT-OBSERVATION METHOD
In my use of this method in forested areas in northern Michi-
gan it was necessary to modify the method on account of the vary-
ing heights of the plants. Customarily, layers or stories were
selected and each story was considered as an integral point-
observation quadrat. The layers most frequently used were : the
high trees, which in a dense forest would give complete coverage;
medium or small trees, if necessary; high shrubs; medium shrubs;
occasionally low shrubs; herbaceous levels, especially at about a
meter in height in areas in which Pteridium latiusculum (Pteris
aquilina) was abundant at the Pteridium level; a ground level
just above the ground; and, if necessary, the actual ground, in
case it was not bare. As many of these different stories or levels
were selected in each case as seemed necessary and the categories
of plants were varied as the occasion demanded.
28 FIELD MANUAL OF PLANT ECOLOGY
Exercise 9. Forest Modification of the Point-observation Method
Use the same sort of setup as in Exercise 8. Establish the
categories in each of the levels desired and follow the same pro-
cedure for each of the categories in each of the levels.
A sample of data follows :
Aspens,
Point-observation Data
East of Gorge, Douglas Lake, Michigan, July 3, 1940, Ecology Class.
(The recorded values are one-half the number of units observed,
therefore giving the percentage coverage per square meter.)
Categories selected
Point-observation quadrat
Percent-
age
cover-
age
I
0
0
41
(34)
(6)
(1)
0
0.9
(0.8)
II
96
(96)
0
22
(22)
2
(2)
27.6
(17)
(6)
(1)
(0.1)
(0.5)
(3)
III
25
(25)
0
24
(24)
0
24.8
(8)
(1)
(1.4)
(0.4)
(14)
IV
0
0
32
(32)
0
13.8
(7)
(6)
(0.8)
V
34
(20)
(14)
0
33
(33)
0
6.7
(6)
(0.7)
VI
50
(50)
0
64
(64)
12
(12)
19.4
(14)
(2)
(1.6)
(1.8)
VII
25
(25)
18
56
(56)
1.3
(1-3)
5
(2)
(2)
(1)
VIII
0
2.2
22
(22)
0.9
(0.9)
18.5
(2)
(0.9)
(0.3)
(5.3)
(10)
(22)*
IX
0
0
20.3
(14)
(2)
(4.3)
0.4
(0.4)
52.2
(1)
(2.3)
(0.1)
(47)
(1.8)
X
17
(17)
0
38
(38)
0
89.5
(6)
(2)
(0.5)
(80)
(1)
24.7
Pinus resinosa
Populus grandidentata ....
10.1
Pteridium level
Pteridium latiusculum. . . .
Populus grandidentata ....
35.2
Rhus glabra borealis
Vaccinium pennsylvanicum
1.7
V. pennsylvanicum
25.8
Grasses (Oryzopsis, Dan-
thonia, Panicum meri-
dionale)
Vaccinium pennsylvanicum
Stems
Pteridium latiusculum . .
Populus grandidentata . .
Pinus resinosa
(0.1)
Lichens
Stump
* Not counted as living coverage.
PERMANENT QUADRATS1
Where long-time studies are desired, it is necessary to locate
permanent quadrats. The usual method is to mark by driven
stakes, preferably with iron pipe, the four corners of the quadrat
area. The stakes should be long enough so that there is no chance
1 Cf. also Weaver and Clements, op. cit., pp. 26-29.
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 29
of their being withdrawn accidentally. Whenever a count is made,
any of the methods may be employed. Such permanent quadrats
may be located anywhere with or without any special protection.
It may be advisable, particularly if the permanent quadrat is lo-
cated in a place likely to be disturbed, to fence off an area around
the permanent quadrat. Normally permanent quadrats are ex-
posed to whatever agencies are operating in an area.
Exercise 10. Permanent Quadrats
If opportunity presents, establish one or more permanent
quadrats, as indicated above, or record the data from one or
more which have already been established. Use any of the meth-
ods which have been presented, such as list quadrat, count quadrat,
charting by squares, photographing, or charting by pantograph.
DENUDED QUADRATS1
In order to study the details of revegetation following the re-
moval of vegetation, a permanent quadrat may be set up and the
vegetation removed by burning, flooding, salting, covering, or by
excavating the top 1 to 6 inches of the ground. Such quadrats
may be started at different times of the year to bring out differ-
ences for which the season of initiation might modify the results
which follow.
Actual revegetation may be obtained naturally {i.e., without
human interference) as seeds or disseminules get into the area
from the surroundings, or in other experiments the normal re-
vegetation may be modified by sowing seeds, planting parts, se-
lective weeding, or by different types of fertilizer treatment.
Exercise 11. Denuded Quadrats
If time permits and there is opportunity, denude in various
ways the vegetation from certain permanent quadrats and ob-
serve the results in the following weeks and years.
CLIP QUADRATS2
In order to simulate grazing or to ascertain the amount of
vegetable matter produced, the vegetation from a square meter
1 Cf. also Weaver and Clements, op. cit, pp. 29-30.
2 Cf. Weaver and Clements, op. cit, pp. 18-21.
30 FIELD MANUAL OF PLANT ECOLOGY
is clipped off. The clipping may be done at the ground level or
at various heights above it, depending on the purpose of the
work. The clipped material is dried in the oven at a tempera-
ture from 100 to 105°C in order to obtain the amount of dry matter
developed by the plants in the selected area. Results may be
obtained for individual species of plants as well as the whole mass
of vegetation. More than one clipping during the year will have
to be made.
Although such clipping is not exactly equivalent to grazing, it
is a useful method by which to obtain the yields of plant material
and thus make comparisons between areas possible.
Exercise 12. Clip Quadrats
If feasible, obtain the ovendry weight of the forage clipped
from designated square meters of ground in accordance with the
suggestions above.
TREE COUNT
In forested areas it is customary to count the trees separately
from the ground plants. The distinction is arbitrary, a common
one being that all woody plants more than a meter high are in-
cluded in the tree count. If the woody plants are shrubs, the
assembled data are divided accordingly, as will be seen later.
SIMPLE TREE COUNT FOR FREQUENCY
The simplest tree count is the counting of some unit number,
say the first 100 or 200 trees as one comes to them. This may be
done by projecting a straight line through a wood, by helter-
skelter movement, or by any special pattern desired. The advan-
tages are that no account need be taken of area or direction, nor
of exact size. Among the disadvantages is the fact that the area
occupied by the unit number of trees may be quite variable in
different sets. This might interfere with an accurate determina-
tion of the frequency and does make comparisons between differ-
ent areas less significant.
Exercise 13. Tree Count
Following a path decided upon (straight line, inverted V,
circle, or other pattern) , name and count the trees that are within
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY
31
a meter on each side of the path, until a prearranged number has
been counted. If half or more of the trunk at the ground falls
within the strip, such a tree should be counted. If there are not
that many trees available, count all that are present and use the
total number in calculating the percentage. Record as follows:
Species
Number*
Totals
Acer saccharum . . . .
Betula lutea
Fagus grand if olia . .
Fraxinus americana
Ostrya virginiana . .
Tilia americana . . .
'TmTWTHlimTHJTHtTHlfWTmTtU///
mill
mtf+UTtHttU/
rwm/n
ii
nu
53
7
21
12
2
5
Total
100
* Since 100 trees were counted the numbers of each are also the percentage frequency.
Exercise 14. Tree Count with Diameter Classes
Repeat Exercise 13, but record the trees by diameter classes
as shown below.
Species
Diameter
class, cm
Number
Totals
Acer saccharum
Betula lutea
0-10
11-20
21-30
31-40
41-50
21-30
31-40
11-20
21-30
31-40
0-10
11-20
0-10
31-40
mi mi im mi
mi i
in
mi mi
mi rm mi
mi
in
ii
rm ii
mi mil/
mi ii
mi
ii
mi
20
6
3
10
14 53
4
Fagus grandifolia
3 7
2
Fraxinus americana
Ostrya virginiana
Tilia americana
Total
7
12 21
7
5 12
2 2
5 5
100
The diameters may be estimated by placing a measuring stick
in front of the tree and standing off a little distance, or more easily
32 FIELD MANUAL OF PLANT ECOLOGY
by using tree calipers. Since the diameter equals the circum-
ference divided by w, a tape may be graduated to read diameters
by marking off multiples of 3.14 for each linear unit of diameter.
The following table shows the graduations for the first ten units,
inches if inches are used, or centimeters if the metric system is
used.
Units
Units
Units
Units
Diameter
Circumference
Diameter
Circumference
1
3.14
6
18.85
2
6.28
7
21.99
3
9.42
8
25.13
4
12.57
9
28.27
5
15.71
10
31.42
AREA TREE COUNTS OR TREE QUADRATS
Counting all of the trees in a definite area is a standard pro-
cedure in small forests, while in a larger forest definite quadrats
may be set up. By dividing the number of each diameter class
of -each species by the total number of trees counted, one ob-
tains the frequency. The size of the area may be varied, de-
pending upon the type of forest. The area is always larger than
that employed for ground plants since trees do not mature so
close together. A quadrat 10 meters on a side has been found con-
venient in temperate regions, although local conditions may make
some other size more useful. In many studies the figures are ex-
pressed on the basis of certain unit areas as per hectare, per acre,
per tenth acre, or other unit, A^very common practice, particu-
larly in forestry, is to use areas 66 feet long and. 66 feet wide
(equals }{q acre) in which the height, diameter, and the kind of
trees are all taken.
Where statistical studies are planned, any definite area may
be charted in accordance with the following simple procedure:
the area on the ground having been laid out, strings or small
ropes at suitable intervals are run through the area. A team of
two students charts on cross-ruled paper the exact location of
each tree, giving the name and diameter. Such areas are re-
charted at later periods to show the history of the area. Meter
quadrats may be located within these areas to record the ground
plants as well.
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 33
Exercise 15. Area Tree Counts
Stake out definite areas and locate squares as in Exercise 7.
Count by species, species classes, or on cross-ruled paper chart the
trees by name and class.
SPECIAL-PURPOSE TREE COUNTS
When it is desirable to know the frequency of some particu-
lar tree, a tree count may take cognizance of that particular spe-
cies and lump all the others under such a designation as " other
trees." The same method may be used for the presence of seed-
lings of trees.
Other uses suggest themselves.
TREE COUNT DONE BY STUDENT CLASSES
When classes of students take tree counts, the simplest pro-
cedure is to line up the members of the class on one side of the
area and give each definite directions as to which way and how
far to proceed in his count. Groups of two are most satisfactory,
the lead one counting and naming the trees as he proceeds for-
ward, the second person remaining on the spot as long as possible
to record trees and distance and maintain correct direction. Be-
fore the lead person is lost sight of, he should stand still until the
recorder comes up to him and checks direction ahead. In such
counts both the number and kinds of trees as well as the diameter
classes may be taken. A simple means of maintaining a proper
strip in case one doesn't wish actually to lay down strings in the
landscape is to use two metersticks, which are held by the lead
person horizontally at meter height, one stick in each hand. As
he proceeds, any tree touched by either stick is counted, and since
the two sticks are not fastened together, it is possible to go through
a forest without much difficulty.
The primary purpose of the tree count is likely to be three-
fold: (1) the kinds, i.e., the species represented, (2) the numbers,
and (3) the sizes. The sizes of the trees include the height and the
diameters breast high (DBH), i.e., 4.5 feet above the surface of
the ground. Height may be expressed in actual figures but is
much more likely to be divided into such categories as seedlings,
34
FIELD MANUAL OF PLANT ECOLOGY
small saplings less than 2 meters high, between 2 and 7, between
7 and 10, between 10 and 30, and above 30 meters. These are
almost always estimated, although if down trees are present they
may be measured directly, or if a hypsometer is available, it may
be sighted to give the height of the tree. Likewise, if it is not pos-
sible to get the shadow of the tree, one can take advantage of the
fact that the tangent of an angle of 45 degrees is unity, as shown
in the diagram (Fig. 3) . Locate a 45-degree triangle on the ground
Fig. 3. How to find the height of a tree. CA equals BA, when the angle ACB is
45 degrees.
so that its hypotenuse projected will hit the top of the tree. The
distance of the ground point from the base of the tree (CA) is
the height of the tree (A B). The diameter, which is taken
breast high and expressed as DBH, may be taken directly to the
nearest inch or centimeter but in general is taken within certain
classes. A little experience enables one to estimate it quickly,
but doubtful cases had best be measured with tree calipers.
Trees which are not cylindrical will require such measures at right
angles to each other, the figure recorded being the average. The
usual classes measured include saplings which are under an inch
(2.5 centimeters) in diameter, then 1 to 2 inches (2.5 to 5 centi-
meters), 2 to 4 (5 to 10), 4 to 8 (10 to 20), and continued in mul-
tiples of 4 inches or 10 centimeters. Notations regarding any
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 35
observation or determinable facts about trees may be made on
the spot and included in an annotated list.
When the class has finished taking the tree count, the figures
should be grouped together to give the percentage of trees of each
species in the classes of height and diameter for given areas.
Tree counts taken in this manner are ready to be used in vegeta-
tion formulas.
Exercise 16. Class Tree Counts
Following the directions given above, groups of students will
make tree counts in prearranged lanes in a given area and assemble
the results into one table.
Note: For the average class in field ecology the usual field
procedure in studying any forested area will include a tree count
by one or more of the procedures mentioned above, by each team.
The data of all the teams will be assembled to show at least the
number and percentage of each of the various kinds of trees on
the area selected. The data may be in the form of tables or they
may be accompanied by charts or diagrams. On the same area
a suitable number of ground-plant quadrats will also be taken
and tabulations made of the frequency of the species found.
Such studies will be supplemented by data on such other items
as: soil, physiography, drainage, hydrogen-ion concentration,
climatic conditions, local factors — all aimed to present an ade-
quate portrayal of the area studied.
Thus by combining one or more of the quadrat methods with
one or more of the tree-count methods, studies of several plant
communities or of several examples of an association may be con-
ducted through a summer to gain an insight into the vegetation
of a region.
OTHER METHODS OF DETERMINING FREQUENCY
THE STRING METHOD
A piece of string or twine may be stretched between two stakes
just above the ground vegetation. Plants whose crowns come im-
mediately under or over the string are then counted and the fre-
quency determined by dividing the number of each species by
the total number of plants counted. This may be varied to include
an area between two strings stretched, say, 10 centimeters apart.
36 FIELD MANUAL OF PLANT ECOLOGY
Exercise 17. Determining Frequency by the String Method
By following the directions suggested above determine the
frequency of various plants by the string method.
Note : If instead of merely noting the presence of plants along
the line or within a short distance from it the thickness of the
plants is measured, this method becomes the line-interception
method (page 36) and yields both frequency and density in ad-
dition to position along the line.
If the plants at the line are recorded by name in order of oc-
currence, it becomes a transect (page 43).
LINE-INTERCEPTION METHOD OF SAMPLING VEGETATION
(Modified slightly from Canfield)1
In this method advantage is taken of the fact that, for a given
area, rectangular plots longer than wide give a better sampling
than square quadrats. The line carries this idea to the possible
limit. The bearing and the location of the ends of the line for
samplings are set up in accordance with a prearranged plan to
obtain random samples. The line is stretched and staked firmly
in position in the area under consideration. The line is considered
to have indefinite length and vertical extension, but lateral width
is limited to 5 millimeters on either side, although it is better to
use 10 millimeters on one side.
For simple frequency, each plant that is intercepted by the
line is recorded according to species. The number of times the
species is intercepted divided by the number of plant intercep-
tions is the frequency. This is usually expressed as a percentage.
To measure the density of the vegetation, as each plant is
met (intercepted by the line) the name and the diameter on the
line are recorded. The measurement includes only the intercept
of the vegetation encountered, as shown in Fig. 4. Shrubs may
be measured both at the surface of the ground, if intercepted,
and at the diameter of the crown in the vertical plane above the line
(crown intercept). The same plan will need to be used if a tree
layer is present.
Canfield, R. H., "Application of the line-interception method in sampling
range vegetation/' Jour. Forestry, 39:388-394. 1941.
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY
37
The assembled data will show for each species — or each
group, if certain species are grouped — the total linear extent in-
tercepted by the line in appropriate units. Dividing this by the
Fig. 4. Side view of a line in the line-interception method, showing the plants at
or within a short distance of the line AB. Below, in three levels (T, tree; S, shrub;
and G, ground) are the projections, heavy lines showing the part to measure in each
level. Note : four plants that show in the side view but are not within 1 centimeter
of the line are not to be measured. The trunk of the tree, which happens to be on
the line, is measured as a transgressive in both the shrub and ground layers. Only
the parts of clumps or patches of ground plants that are within 1 centimeter of the
line are measured, irrespective of the total extent of the patch.
length of the sampling unit and multiplying by 100 gives the
percentage of ground occupied. Dividing the length for each
species or species group by the total length of that level of plants
and multiplying by 100 gives the percentage composition.
This method has a variety of uses but has been used most
38
FIELD MANUAL OF PLANT ECOLOGY
expeditiously in grassland work to measure composition, density,
forage utilization, and forage volume. It has the advantage of sim-
plicity in training crews for work both in the field and in the office.
Exercise 18. Line-interception Method
Set up a plan for locating lines along which to take the data.
If but a single area is to be studied, space starting points along a
line about 3 meters in from one edge and lay out parallel lines at
right angles to the starting line. The length of the lines may de-
pend upon how many there are, but 15 meters or 50 feet is quite
satisfactory. Experience indicates that twice as much length is
necessary to give a fair sample if the density is below 3 per cent
than if it is above 5 per cent. If several areas are to be sampled,
set up the same arrangement of lines in each and make them the
same length.
Procedure: From the starting point proceed along the line,
recording the width of the stem or clump at the ground for each
herbaceous plant within 10 millimeters of the line and the inter-
cept of the upright plane with the crown of each shrub or tree.
Each species may be treated individually, or if only certain ones
are vital to the study, others may be grouped in various fashions ;
e.g., if a lawn were being studied the weeds could all be grouped
together.
After the field data have been gathered, they should be assem-
bled by teams for the whole class. From the total length meas-
ured, the percentage of the line occupied by the different plants
as well as the different types of vegetation can be calculated.
Sample of Data by Individual Group
Group No.
Place . . .
1 Date . . . J.ul.y. 7'. 1?47. . . . Elapsed time
Aspens east of the Gorge
65 min.
Length of strip in mm Width of strip
10 mm.
Species
Occurrences (expressed as length of each
in millimeters)
Totals
Plant A
15, 20, 10, 13, 12
2,1,3
3, 5, 40
7, 10, 17, 9, 17, 20, 14
5 (70 mm)
Plant B
3 (6)
Plant C
3 (48)
Plant D
7 (94)
18 (218)
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY
39
Summary of Class Data
Species
Group
Occurrences
Length, in mm
Totals
Plant A
5
(70)
1
II
III
78
45
(507)
(420)
> 241 (2327)*
IV
113
(1330)
,
Plants
3
(6)
\
II
III
78
(90)
> 98 (104)
IV
4
(8)
J
Plant C
3
(48)
\
II
III
3
(37)
6 (85)
IV
J
Plant D
7
(94)
II
III
45
52
(340)
(390)
> 118 (1024)
IV
14
(200)
Length of strip, in mm
30,000
II
III
30,000
33,000
> 122,000
IV
29,000
-
* To obtain the length in meters, multiply by 0.001.
To obtain the area of the strip in square meters, multiply the length in meters by 0.01, since
the strip is 1 cm wide.
To obtain coverage, divide the length obtained for each plant by the total length of the strips.
To obtain frequency, divide the number of occurrences of a given plant by the total occurrences
of all plants.
THE METHOD OF SQUARES BY USE OF A FRAME
A framework 1 meter long by 1 meter wide, subdivided into
10-centimeter squares, may be made of wood and twine or wire
and set down over the vegetation at selected spots. The presence
of each species in the various squares is then determined. Divid-
ing the number of squares in which a plant was present by the
total number of squares (100) gives the frequency. This method
may help in taking count quadrats but is more laborious than
taking list quadrats. The vegetation must be low and without
shrubs and trees, to permit its use.
Exercise 19. Frequency by the Method of Squares by Use of a Frame
Make a framework 1 meter square with strings or wires strung
each way at 10-centimeter intervals. Place it over vegetation at
40 FIELD MANUAL OF PLANT ECOLOGY
designated spots. Determine the presence of the various species
in each square. Divide the number of squares in which each
species occurs by the total number of squares (100) to obtain the
frequency for each species.
Circular hoops or other shapes may be employed. Such a
hoop thrown from place to place in grain fields is used to deter-
mine disease frequency. A count of the diseased plants within
the hoop in comparison with the total number of plants within
the hoop gives the disease frequency.
PERCENTAGE AREA FREQUENCY
A frame of squares is laid over the vegetation and the area
that each plant occupies in each square is estimated and added
together and divided by the total area.
Exercise 20. Percentage Area Frequency
Use a frame of squares, as directed above, to determine the
area frequency of the various plants in the area under considera-
tion.
POINT-QUADRAT METHOD
A method of determining frequency by obtaining statistical
data in accordance with a plan which will not vary with different
operators was developed by Fred W. Tinney, O. S. Aamodt, and
Henry L. Ahlgren in a "Preliminary report of a study on methods
used in botanical analyses of pasture swards" (Amer. Soc. Agron.
Jour., 29:835-840. 1937).
A framework, 1 foot high or more, is built as shown in Fig. 5.
Wire pins about 14 inches long are put through sets of holes which
are 2 inches apart. In operation the frame is set down over the
vegetation and the pins pushed down until they touch the plants.
In one method the worker records only the first plant which is
touched by a pin. In a second method the pin is pushed on and
on until it hits the ground, scoring for each plant touched. After
completing the scoring of the first pin, the second is pushed down
and so on. This apparatus may be built or set so that the pins
form an angle with the ground. An angle of 45 degrees with the
ground is perhaps the best to employ. Photographs of either may
be taken.
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY
41
Instead of movable pins the framework may be built with fixed
wires from top to bottom. In use this frame is held at a 45-degree
angle from the ground. The plants which touch the wires are
counted.
Exercise 21. Point-quadrat Method of Determining Frequency
Set up the apparatus figured below along a line through veg-
etation. Score the "hits" made by the points on the different
i
i
i
l_Li
Fig. 5. Apparatus for taking point quadrats (explanation in the text). A pair of
side arms may be provided to tilt the frame 45 degrees.
plants. The " hits " recorded for each species divided by the total
number of hits of vegetation by the pin points used gives the fre-
quency.
COMMUNITY COEFFICIENT
In order to make statistical comparisons between parts of a
given area, or between different areas or associations, community
coefficients have been developed. Cojtnmunity coefficients are
simply numbers expressing resemblance. As originally developed
byJaccard,the numbers, according to American experience, seemed
too low. Consequently an adaptation was made by Gleason.
He used the frequency index instead of just the occurrence and
obtained what we shall call the FICC (frequency index commu-
42 FIELD MANUAL OF PLANT ECOLOGY
nit^_c_Qefficient) . The basic method of obtaining the coefficient is
the same in either case, but in JaccarcTs system a number 1 is
used for each species concerned, while in Gleason's plan the pre-
viously determined frequency index is used in dealing with each
species.1 This gives greater weight to species more frequently
found.
To compare two areas, set up three columns. In the first
put the frequency of each species that occurs in the first area
only; in the third column the frequency of the species that occur
in the second area being compared only, while in the second col-
umn put both frequencies of species that occur in both areas 1
and 2. Add all the columns and divide the central column, which
contains the data for the species common to the two areas under
comparison, by 2. To obtain the coefficient divide the number
thus obtained (column 2 total divided by 2) by the total obtained
by adding this number to the addition of the total of columns 1
and 3 and multiply by 100, as shown in the table in the exercise
following.
The coefficients obtained by the Gleason method yield rela-
tively high figures, usually in excess of 80, if the two areas are
in the same association in the same region. Still one may find
areas close together, appearing similar to the eye, which do not
yield coefficients in excess of 60. The method is open to the crit-
icism that no distinction is made between a species which occurs
in small numbers in a quadrat and one which occurs in large
numbers. However, experience has shown that the approxima-
tion is useful at least in beginning work.
Pictures may be taken of different quadrats to facilitate com-
parison, but pictures fail to yield a number which can be used sta-
tistically.
Exercise 22. Frequency Index Community Coefficients
First determine the frequency indexes of the plants of two or
more areas.
Using the figures for FI thus obtained, fill in a table in the
following manner:
1 Gleason, H. A., " Some applications of the quadrat method," Torrey BoL
Club Bui, 47:21-33. 1920.
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY
43
To Compare
the Plants of Two
Areas
Frequency by area or set
Species
Frequency by area or set
Species
I
Common
II
III
Common
IV
(I + ID
(HI + IV)
Plant A
G
Plant A
15
Plant B
3, 4
Plant B
35
Plant C
5
Plant C
17
Plant D. . .
15, 35
Plant D
56
Plant E
8
Plant E
64
Plant F
20, 20
Plants
57
Plants
30, 6
Plant (?
75
Plants
2
Plant//....
35
Plant/
1
Plant /
2, 2
Plant/
60, 75
Plant J
80
Totals
13
268
9
Totals ....
205
4
223
3^ of Common
= 134
3^ of Common = 2
Common + I -\
- II = 156
Common -f- III + IV = 436
FICC = i%s<
j X 100 = 86
FICC = ^36 X 100 = 0.5
Areas I and II are quite similar, in fact, the same association.
Areas III and IV are dissimilar, i.e., two different associations.
Compare various areas as directed above — not only areas
which are obviously similar, but also areas which are quite dif-
ferent.
TRANSECTS1
Transects may be defined as lines through vegetation. In
early__ ecological work they usually extended across two or more
types of vegetation and were particularly valuable in that they
showed where the change from one type of vegetation to another
occurred. More recently it has been shown that rectangular
quadrats or sample plots longer than wide give better results
than square quadrats. The limit to which this can be carried is
a line. (See The Line-interception Method, page 36.)
Transects may therefore be used to determine composition,
frequency, and density within an association, a plot of ground,
or larger areas, and also to show changes from one type of vege-
tation to another.
1Cf. also Weaver and Clements, op. cit, pp. 33-39.
44 FIELD MANUAL OF PLANT ECOLOGY
There are three common types of transects :
1. The line transect is a cross section of vegetation in which a
line is established from one point to another by stretching a stout
cord or wire between two stakes. All the plants which touch that
line are recorded in the order in which they occur. A person read-
ing over that list and knowing the plants concerned is aware of the
change from one type of vegetation to another. If the line crosses
bodies of water and if the profile is also given, a line transect
shows these changes very well.
2. Instead of a line a belt transect may be made. The only
difference is that an area of definite width, usually small — 5 or
10 centimeters — is used and in this area the plants are listed.
A list is made for each unit of area. It shows essentially the
same facts as the line transect but is more cumbersome.
3. The associational transect is really a belt transect in which
the association only is named instead of the individual plants.
This is advantageous where the line crosses undulating ridges and
swales. Although not difficult to take, it requires previous study
of the vegetation and recognition of its types. For associational
transects areas of various sizes may be used, such as the whole
meter quadrat or an area a meter long and 10 centimeters wide;
or half a meter long and 10 centimeters wide, varied to fit the par-
ticular case; or the actual width of each association the line or
belt crosses may be noted. One student manipulates the string
and sticks and recognizes the plants and the other member of the
team maintains the direction and records the results. If the tran-
sect crosses water, however, and sticks are used, it usually re-
quires three or four students to maintain the sticks in position
while the transect is being taken.
The series of great belts around the world (equator, tropics,
temperate and arctic zones) is really a transect on a grand scale.
Exercise 23. Line Transect
Stretch a stout cord between two stakes set some distance
apart in different types of vegetation. Record in order the names
of the plants touched by the string. When taken from a point
in a lake or stream up onto the shore, the value of a transect is
best shown. It is desirable to accompany the line with a profile
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 45
along it. This may be estimated or developed to scale. (For the
latter see directions under Exercise 49, Surface Profile.)
Exercise 24. Belt Transect
Set up two parallel cords, 10 centimeters apart. Consider
each 10-centimeter square as a unit. Make a list of the plants in
each, unit by unit in order. Belt transects are also best accom-
panied by profiles.
Note: See also The Line-interception Method, page 36.
Fig. 6. A part of an associational transect taken west from Lake Michigan in the
beach area, north of Waukegan, Illinois, in 1909. A, Lake Michigan; B, open sand
of lower beach; C, beachpool with algae; D, open sand; E, Cakile-Xanthium associ-
ation on middle beach; F, Salix dune with Calamovilfa; G, Potentilla anserina
association; H, Salix dune with Juniperus horizontalis; I, Andropogon scoparius
bunch-grass prairie; /, heath with blowout; K, Scirpus americanus association;
L, Scirpus validus association ; M, Typha latifolia association ; N, Castalia-Nymphaea
association; 0, Potamogeton association; P, Little Dead River; Q, Liatris spicata
prairie. Separations are indicated below the line of the profile.
Exercise 25. Associational Transects
Stretch a long stout cord between stakes in a line which may
extend for a considerable distance. Record the associations crossed
either in units of distances or by setting down the width of each
association. If the first method is used, determine the outstand-
ing association in each meter and record. In case more than one
association is present in the meter it is necessary to decide which
is more important to record, or to record both. Often a mixture
must be recorded, i.e., the transition from one association to an-
other. In the second method of recording, measure the width of
the association or mixture first encountered, record, proceed to
measure the second vegetation type until another change is en-
countered, record, and continue (Fig. 6).
Each type of transect is best expressed on cross-ruled paper.
It is always desirable to accompany it with a profile of the sur-
face of the ground.
46 FIELD MANUAL OF PLANT ECOLOGY
MAPPING
In many phases of ecological work it is necessary to use maps.
Often the maps have to be made by the class itself. Several meth-
ods are available, some of which require expensive instruments,
while by other methods maps may be made with the simplest of
tools. Maps are necessary both as base maps on which to put
data to show occurrence and distribution and also for compara-
tive purposes. Since most ecological maps cover a relatively
small area, the basic problem of having to select the right pro-
jection does not arise. Rectangular coordinates will serve all
class purposes. Once a base map has been made, it is a simple
matter to duplicate it by mimeograph and obtain as many copies
as necessary. The habit of making and reading maps is a most
desirable one, not only in ecology, but in any study in which
geography is concerned.
TYPES OF MAPS
1. Simple sketch. Simple sketches may be made from any
point of vantage from which one may see the various parts of
an area and picture them as he sees them. One should, however,
keep in mind that a distance between two points appears to be
smaller when the observer is at a distance from them, than when
he is close to them. Adjustment for this should be made as the
sketch map is drawn. Good practice is for the same individual to
sketch a given area — a pond or a lake for instance — from dif-
ferent points of vantage and compare the maps which he makes.
The disadvantage of sketch maps is that although the scale on a
map is usually considered the same throughout, the corresponding
scale of the ground is likely to become shorter the greater the dis-
tance from the observer. Outlines that are closer to the observer
are easier to draw correctly than those which are farther away
from him, but if the distance is too great even the outlines can-
not be well seen. In spite of their disadvantages, sketch maps
are most useful in taking notes on small areas. Sketch maps may
be made from photographs. The same disadvantages apply,
unless one is skilled in rectifying the scale, as distance from the
observer increases.
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 47
If a suitable base map has been provided, sketching in vari-
ous details is very much simpler and more accurate than if the orig-
inal observer makes both map and details at the same time.
2. Triangulation with the distances measured. Several methods
of triangulation are in standard use in all types of surveying.
In this method the only implements required are a tape or chain
or measuring sticks and labeled stakes to mark the points. For
this method it is desirable to go over the area to be mapped and
put in stakes for the various points. Such stakes should be
plainly visible from the others and are usually indicated by a
flag or piece of cloth, colored or white, to make them more visible.
In using this method one simply measures the distance from 1 to
2, 2 to 3, and 1 to 3, etc., as indicated on the diagram (Fig. 7 A).
This is continued so that there are always two measurements
from each and every point. The data sheet simply states in
column 1 the points, as 1 to 2; in column 2 the number of feet,
meters, or whatever units are used ; and in column 3 any remarks
necessary. This procedure is followed until the points which have
been set up are completed. If the area mapped by this method
is compact, the points may be on or near the periphery. If the
area is more extensive, as around a lake across which the tape
will not reach, the series of triangulation points must be set up
on land around the lake. The degree of accuracy on the finished
map will be checked by noting how closely the end point coincides
with the starting point.
The principal difficulties are in accurate and uniform stretch-
ing of the tape or chain if it is in the air or on uneven ground.
Tapes in air always form a catenary, and the longer the distance,
the deeper the catenary. If a spring is put on one end of the tape
and stretched to the same figure, the results are a little better,
but this is seldom done. If measuring sticks are used and they
are simply laid on the ground, the inequalities of the ground often
make the measurement off a foot or more in a distance of 60 or
70 feet. This can be corrected by putting in posts to maintain the
measuring sticks level. The failure of having the tape or stick
exactly on the zero point and the failure of sufficient accuracy in
reading result in errors. Having two people make the reading as
a check helps mitigate this. If a cloth tape is used, one must re-
48
FIELD MANUAL OF PLANT ECOLOGY
Fig. 7. Some principles of mapping.
A. Mapping with stations and tape. Data for this diagram are as follows:
Points Distance, Ft Points Distance, Ft Points Distance,
1-2 25 2-4 16 4-5 15
1-3 23 3-4 27 2-6 40
2-3 30 2-5 26.5 5-6 24
Ft
B. Roving-point method with base line north-south. The angles for point 1 (solid
line) are from the north compass N 110°, from the south compass N 70°; for
point 2 (dash line) from the north compass N 98°, from the south compass
N60°.
C. Setup for mapping when the base line is on a slant. Base line 50 feet long. At
each end a protractor is oriented north-south. The white thread (dash line) is
looped around the pin at the north end of the base line and stretched at the angle,
N 130°; the black thread (solid line) is looped around the pin at the south end
of the base line and stretched at an angle of N 90°. The intersection of these
two lines is the location of the point P.
D. The traverse method.
Points
1-2
2-3
3-4
4-5
5-6
6-1
The data illustrated are as follows:
Direction Distance, Ft
N 50° 35
N 90° 50
N 140° 15
N 220° 30
N 310° 20
N 269° 52.5
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 49
member that it will shrink if it is allowed to get wet. Another ob-
jection is that in triangulating through a forest, if the original
points have not been carefully located the lines ma}^ run through
trees, which makes it necessary to take the tape around, thus in-
troducing errors or necessitating the relocation of the points.
When using steel tape it is necessary to keep it from kinking.
If wet, it should be dried and preferably oiled slightly before being
put away.
With all the disadvantages, the main advantage is the sim-
plicity of the method and the inexpensive tools which may be
used.
3. Tr {angulation, using a base line and flag stations. This
method of triangulation is suitable for rough country and across
bodies of water. A definite base line of convenient length is set
up and measured. Flag stations for the different key points are
set out in the area. The flag stations must be visible from each
end of the base line. (Note: If not visible from both ends, a
second or subsidiary base line will have to be set up later to get
the cross location of all such flag stations.) The base line should
be on as high ground as possible. It must be measured with con-
siderable accuracy. It is best located so that it will give large
angle measurements to all parts of the area; in other words, to
one side of the area. If it is located in the middle of an area,
there will be points close to the projection of the base line on which
it will be impossible to take data. In operation, a transit, a plane-
table (a drawing board set up on a tripod), or a compass is set up
at one end of the base line. The observer sights to each flag sta-
tion in turn, recording the number of the station, the angle, and
any remarks that are necessary. If a transit is used, the angle is
read on the compass and recorded, preferably from zero clock-
wise to 360 degrees. This means that after each sighting the com-
pass needle must be allowed to come to rest and the reading made
always clockwise from north to the flag station sighted. If a
simple sighter is used instead of a regular transit, then it is nec-
essary to set the planetable definitely by compass. Army plane-
table boards have a compass on the edge which permits orienta-
tion of the board. The north line should be indicated on the map
and checked up during the progress of working as well as at the
50 FIELD MANUAL OF PLANT ECOLOGY
end of the work. If a simple sighter is used on a planetable,
lines may be drawn along the edge of the sighter to indicate the
direction and numbered or lettered for the particular flag sta-
tion, or the angle from the base line to the flag station is read on
a protractor and expressed clockwise as an angle from the base
line selected. These figures are recorded in the notebook against
the number of the points. If distances are great, it may be nearly
impossible to be absolutely certain of the number of the sta-
tion. In such circumstances it is desirable to have a person or
system of signals to relay information that may be needed by the
observer. Occasionally on irregularities in shore lines the next
point may really be back rather than forward and the observer
at the base line may not be able to realize this. More careful se-
lection of points would avoid this, but that would depend on the
area and it may not be possible to obviate it. When one has fin-
ished reading all of the flag stations from one end of the base
line, he moves the transit, sighter, or planetable to the other end
of the base line, setting up exactly over it and repeating the whole
performance. It is necessary to be certain that the observation
is recorded correctly in accordance with the number of the flag
station. When the field work is completed, one has either inter-
secting lines on a map or compass directions or angles from each
end of the base line to each flag station. Lines may be drawn on
the map on the planetable instead of recording angles.
In constructing the map from these data, one needs to esti-
mate about the area covered in accordance with the scale used
and lay off the base line. For class purposes 1 millimeter to 1
foot is a very handy unit to use. From each end of the base line
in turn in accordance with the compass directions or the free
angles from the base line, lines will be drawn. Where these two
lines cross is the location of the flag station. If one has many
points and does not want to draw a multiplicity of lines, a simple
procedure is as follows:
Two people are required but three are better. At each end of
the base line a pin is firmly stuck in the board. On the base line
are set protractors, one at each end, so that angles can be read.
The base of each protractor must be oriented to the proper com-
pass direction. When the two protractors have been located and
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 51
fastened down with pins or thumbtacks, two different colored
threads (white and black) are selected and a loop made in one
end of each and looped over the pins at the end of the base line.
Mapping may then proceed. The mapper reads the angle first
for the white thread, whereupon the person who is managing the
white thread stretches it taut so that the thread passes over the
proper angle or direction on the protractor. Holding the thread
firmly, the mapper reads the angle for the black thread. The
black thread is similarly stretched over that angle on the other
protractor, and where the black and white threads cross the map-
per makes first a little point, then a circle around it, numbering
the point the same as that of the flag station. When all of the
points have been located, they are connected with sketch lines.
If the flag stations are close enough together, this will yield a
highly satisfactory map. If the flag stations are not close enough
together, then one will not know just how to sketch between these
stations. Since that is often the case, it is necessary to take the
map into the field and sketch between flag stations.
4. The roving-point method: triangulation from a base line si-
multaneously from both ends onto a single stadia rod. The setup
for the roving-point method requires a definite base line meas-
ured out in the area. It is advantageous to locate the base line
to one side of most of the area which is to be surveyed. Accurate
location of points where angles are close to the base line is next
to impossible. In operation a planetable with a sighter, a transit,
or a compass is set up at each end of the base line with the re-
corder stationed midway between the two ends. In the field
operation it is desirable to have two stadia rods in the hands of
two stadia men but only one rod is in actual use at one time.
Definite flag stations may be located, but this is not essential.
However, it is desirable to have the students carrying the stadia
rods study the area to be mapped with the director of the party
so as to have a good idea of which points to select. The data
sheet contains four columns: the first, the number of the point;
second, the angle of direction or compass reading from the No. 1
end of the base line or the north end if the base line is ap-
proximately north and south; the third column, the angle or
compass reading from the other end of the base line, or the south
52 • FIELD MANUAL OF PLANT ECOLOGY
end if the base line is approximately north and south; a fourth
column for any notes that may be relayed back to the recorder.
In this method if the stadia rodmen get any distance away it
is very important that the number of the points be maintained
with considerable care. This is particularly so if the two ends of
the base line are out of shouting distance from each other. A
satisfactory arrangement for a class mapping a pond or a hook
point is to have the base line 100 feet in length and the recorder
midway between. An order of procedure is set up and maintained.
In taking the observations, the stadia rodman sets up the stadia
rod strictly vertical at point 1, which if a lake is involved may be
at the shore; if it is another situation, it might be the location of
a certain plant or some other feature. In either case, what it is
should be shouted or relayed back to the recorder to put in the
fourth column. If this is not possible, the number of the point
should be recorded by the stadia person together with any nec-
essary remarks and transferred to the record book later. A check
on the number of the point needs to be made frequently; other-
wise unrectifiable errors are introduced. When the stadia rod is
vertical at the point selected, both compass men sight their
compasses or transits on the stadia rod, allow the needle to come
to rest, and read the compass direction or angle clockwise. The
No. 1 end reports first to the recorder, who acknowledges by re-
peating the number and setting the number down in the proper
column. The No. 2 end then reports, followed by the same sort of
acknowledgment. As soon as both compass readers have reported
and the data are entered, either the recorder or one of the com-
pass men who is in sight of the stadia rodman throws both his
hands up over his head, indicating that that point has been taken.
The only other movements the compass men should communi-
cate to the stadia men are movements of one hand to indicate
necessary straightening of the rod. While the first point is being
taken, the second stadia man has gone to the second point and
sets up his rod as soon as the first point is cleared. Simultaneous
readings are taken of this point and recorded, stadia man cleared,
and meanwhile the first stadia man has proceeded to and set up
for station 3. This procedure is continued until data are obtained
from each point desired. The actual mapping is done in the class-
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 53
room from these data by the same method that was employed
previously, viz., the setting up of the base line in accordance with
the scale selected on a map and the use of black and white threads
to form the intersections (Figs. IB and C).
Disadvantages: A good compass is required on which angles,
preferably to at least half degrees, can be read easily. If any of
the points are located where they cannot be seen from both ends
of the base line, the point cannot be taken. If the point is neces-
sary, it requires setting up a subsidiary base line or a traverse
method from one of the known points. Another disadvantage
occurs where, as in some lake surveys, there is no communica-
tion between the two ends of the base line; here there is always
the chance that the numbers and stations will not agree. Tele-
phone connections set up in the field may obviate this, or the wig-
wag system of signal flags may be employed, or a signal lamp
using the Morse code may be used.
Advantage: The special advantage of the roving-point method
is that it is an easy method for a class to learn, that it gives points
very quickly, and plenty of them, so that they may be close to-
gether— a distinct advantage in mapping — and that it offers
the possibility of locating stations where no flags may be put or
maintained. Where depth to bottom of ponds or lakes is meas-
ured, this is virtually the only method that can be employed.
A modification of having the compasses on the raft to shoot
to some point on the land edge is sometimes employed, but only
rarely is the raft sufficiently stationary to permit this being done.
The usual method is to have compasses located at both ends of
a base line on shore, while on the boat one person in the party
has flags which are held in certain positions, viz., a get ready po-
sition, a take position, and the clear position. The take is usually
an upright flag and the clear is a down flag. In practice a sound-
ing lead is thrown out ahead as the boat moves slowly. With the
lead on the bottom, the rope is maintained just taut but at an
angle. As the boat passes over the lead the angle at the level of
the water becomes a right angle. The depth is noted and the two
compass parties on the shore sight and read the direction or angle.
The number of each point must be the same for both boat and
land parties. Occasional checks, however, are necessary to see
54 FIELD MANUAL OF PLANT ECOLOGY
that the point numbers agree. Several such lines may be run
across bodies of water, taking depths at intervals. The mapping
follows the same procedure as given above.
5. Triangulation departing from a base line, with angles or di-
rections. This method of triangulation may be used to cover long
distances. It differs from method 3 in that the base line is used
directly only in obtaining points at the beginning of the survey.
The base line itself may be quite long, even miles in length. A
base line must be set and accurately measured. Then from one
end to a prearranged point or flag station, which is quite likely
to be a hill or some prominent point in the landscape, direction
is accurately taken. Another landmark is also taken. Then one
proceeds to one and then to the other of these points and takes
the angle or direction on the others. Continuing this process,
triangles are built up in whatever direction and over whatever
area it is required to form the base map. It is only necessary that
each of the points be visible from two previous points. The data
sheet will read: number of the point, other point to point, such
as A-B, A-C, B-C, C-D, B-D, etc. To start with, the first
point has had the angle or direction taken from both ends of the
base line and the second point at least from one end of the base
line. After that the base line may not be used. In mapping, the
base line is located and scaled at what is thought to be a con-
venient position on the map and the mapper will then lay out
the angles for each point. The intersections of the angles from
any two points will be the location of the third point. After the
map has been constructed, distances that are desired may be meas-
ured directly in accordance with the scale. For covering a large
territory such as counties or states, or work in mountains where
ground measurements are impossible or difficult, this is a standard
method to use. The disadvantage is that it requires a good tran-
sit and accurate observation. It may require some difficult trail
cutting to get to the point selected and may take a good deal of
time; for instance, in using such a survey in the Rocky Moun-
tains there might be more than a week between the taking of one
point and the next. The advantage of course is that it lays a foun-
dation for mapping of large areas for other uses. It would or-
dinarily not be used by an ecology class.
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 55
6. Traverse (follow around; direction, distance). The method
of traverse surveying requires a compass and tripod — the better
the compass and the firmer the tripod the more accurate the re-
sults— and a measuring tape or chain. From an ecological
standpoint simple traverse mapping involves starting from a point,
taking a compass direction on another point, and measuring the
distance from the compass to the next point. A stake should
be put in the ground at least temporarily. The compass is then
moved to the point taken and another point sighted for direction
and distance measured. This procedure is continued as far as
necessary for the work in hand. If a traverse goes around a
body of water, the final point should coincide with the original
point. The method of traverse is particularly adapted to going
through woods where the length of the different points can always
be adjusted to what can be seen, thus avoiding the difficulties of
triangulation (Fig. 7D).
Data may best be expressed in the following form: column 1,
the two points between which the information is obtained, such
as 1-2, 2-3, 3-4, etc.; column 2, the distance; column 3, necessary
notes. In taking the distance the tape or chain should be as nearly
level as possible as changes of elevation will make a difference on
a fine map. On ordinary ecological problem classwork this would
be important only if hillsides were included. At the same time
the traverse is taken, change of elevation may also be taken.
If trails are to be mapped or the edges of associations, the traverse
method is the simplest to use.
7. Planetable and telescopic alidade. Where available, this
expensive apparatus is preeminently suited for making detail
maps of many points within range of the instrument. A tele-
scopic alidade is essentially a telescope mounted on a straight
edge, but capable of being moved in a vertical plane. A system
of cross hairs makes certain measurements possible. For the
average class it is better not to use this method where distances
exceed about 800 feet. The particular advantage of the method
is that when the field work is done, you have the map before you.
A large planetable set up on a strong tripod firmly anchored is
leveled off, a pin inserted in the board at the base station. Lo-
cating the pin may require a little preliminary measurement to
56 FIELD MANUAL OF PLANT ECOLOGY
keep the area to be mapped on the board. The edge of the alidade
is then kept in contact with the pin. In taking the points a
stadia rod graduated into feet and tenths is used. For class pur-
poses those stadia rods in which the feet are marked in red and the
tenths in black are objectionable as soon as you get about 400
feet away from the instrument. The stadia rod must be long
enough so that readings of distance may be made. To read as
much as 800 feet would require for the full measurement a rod
at least 8 feet high (more if the bottom of the rod is not visible
to the observer) . The stadia rod is set up on the numbered point
and sighted through the telescopic alidade whose edge is touch-
ing the pin. When the perpendicular hair in the instrument co-
incides with the stadia, the alidade is leveled, if levels are to be
taken, and then read. Great care must be exercised not to touch
the instrument or the legs of the tripod. In reading the instru-
ment there are three cross hairs to be read quickly. The middle
cross hair is the level and the distance between the upper and lower
cross hairs gives the distance that the stadia rod is from the focal
plane of the alidade. That distance is a little over a foot in front
of the alidade. (A statement of focal length accompanies the
instrument.) In class practice it is a good habit to read the upper,
the middle, and the lower cross hairs to a recorder who immedi-
ately subtracts the two halves, i.e., the middle reading from the
upper and the lower reading from the middle. If the figures are
the same or different by less than a tenth of a foot, the point may
be considered accurately read. The distance from upper and
lower hairs, as read on the stadia rod, is then laid off along the
edge of the alidade which has not been moved from the sighting
in accordance with the scale selected. That is the location of
the point. Any notations that need to be made can be put right
on the map. Likewise the value of the level should be entered
near the point. As soon as this is done, the usual sign of clearance,
waving both hands over the head, is given, and the same or an
additional stadia rod is set up for another point. The procedure
is continued until the map is made. One special advantage par-
ticularly in outlining clumps of vegetation or of fine indentations
of shore line within range is that if there is any doubt as to where
the line should go, another point may be taken immediately in
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 57
the field. Another advantage is that direction and distance are
obtained in one operation.
Each person in the group should have a chance at each of
the duties, e.g., reading the instrument, calculating, holding the
stadia rod, or holding intervening vegetation aside when neces-
sary to make a reading possible. For a good map, it is much wiser
to train the reader (sighter) with a few preliminary points and
let him do all the reading until all the important part of the map
is completed, then let other students have their turn at putting
in points. Since the original setup is usually selected on the
ground, it may be a wise thing to locate it, if possible, from cer-
tain landmarks, but this is not absolutely essential for mapping
bogs or ponds as far as the map is concerned.
The main disadvantage of alidade planetable mapping is that
it utilizes an expensive instrument that requires great care in
reading. It cannot be used in rain unless a shelter can be built
over the planetable. When finished in the field, the map is done.
There are therefore no data to give to a class in the laboratory
from which to construct a map.
8. Contouring. In making contours two types of surveying
may be employed. The location of definite points may be gotten
by any one of the above methods and levels run between the
points. A very common method is to use a combination of the
traverse and contouring methods. For this purpose a line is set
up at right angles to a section line or other line agreed upon and
traverse run at intervals. Along with the traverse at either regu-
lar or irregular but measured distances, the elevation is taken.
Where sections are surveyed in the field, traverses a quarter of a
mile apart are often used, or they may be closer or farther apart,
depending on the situation. When the field data are assembled
in the laboratory it is necessary to lay out the base map and
put in the figures of elevation. Smoothed out contours may then
be drawn. While laboratory work in some types of topography
may yield a satisfactory map, it is wiser to check the map on the
ground. This is particularly necessary in case of streams enter-
ing the picture where the contours should be run upstream in
crossing. If there are hills or other points of vantage, artificial
or natural, the job of contouring is simpler. A well-made con-
58 FIELD MANUAL OF PLANT ECOLOGY
tour map is extremely useful in illustrating data of various sorts,
such as distribution of certain types of plants or plant associa-
tions, or laying out experiments, etc.
9. Photography. Wherever a point of vantage obtains, photo-
graphs may be taken of the landscape. From such photographs
a skilled person may construct a usable map. The points to re-
member are that in each photograph there is perspective, and al-
lowance must be made for this in laying out the map. If it is
possible to take a photograph from more than one point, it is ad-
vantageous to do so. The amateur may try his hand, but if there
is an accurate map available he will usually find that, although
photography may be advantageous in arranging details, his basic
outline map will not be nearly as good as he expected. When one
has no other choice in the matter, photography may certainly be
used. In mountain work suitable filters are of great advantage
in penetrating the haze often present around mountain peaks.
10. Aerial photography. The taking of pictures from airplanes
makes it possible to map a considerable area of ground in a very
short time, but if there is no control on the ground, i.e., accurate
surveys made on the ground, with landmarks that can be recog-
nized in the aerial photographs, the maps that result will not be
so useful as may be desired. In taking a series of maps it is im-
portant that there be a reasonable overlap and that the same angle
be employed, which theoretically should be a right angle, although
a slant will make certain features more discernible. From the
negatives prints are made on gelatin which can be stretched. Pri-
mary traverses and triangulations in the area locate landmarks.
The gelatin is stretched or skewed to make these landmarks on
the gelatin fit the landmarks on the ground. This matching when
completed is then photographed and this photograph is the air-
plane map that will be used. Difference in density of the original
negative or of the prints makes it appear as an overlapping patch-
work which can hardly be avoided, but from this map a black-
and-white or blue-and-white tracing may be made which will
serve as a map to use. Without control on the ground the re-
sults are distinctly unsatisfactory.
In mapping vegetation by air different plants have a different
appearance, so that an airplane map shows lines of transition.
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 59
If, however, one does not have ground control, he may later dis-
cover that some of the lines were not different types of vegeta-
tion but merely different ages, or he may have failed to get the
edges of the vegetation in case the appearance was similar. In
general a line between conifers and hardwood vegetation shows
very well. For resurveys aerial photography is particularly ad-
vantageous as a great deal of information is obtained instantane-
ously and many comparisons may be made. In rough country,
likewise, by aerial photography one may be able to get data for
a whole district in a few minutes whereas a whole summer or more
might be necessary to map it by the ordinary surveying methods.
Again, let it be repeated, without ground control the aerial map
may be considerably off.
Note : The average class will not be able to make aerial maps
by* themselves, but it is often possible to obtain prints of pieces
that can be organized into a map. New techniques and instru-
ments for viewing aerial photographs have been developed and
used to good advantage in the Second World War. If available,
use by advanced students in special problems is advantageous.
Exercise 26. Mapping or Map Making
Using one or another of the methods dealt with above make a
base map of an area selected.
Repeat using another method and another area.
After making a base map, put on it (possibly with color)
suitable items of interest, such as particular trees or other plants,
types of vegetation, transition lines. Indicate location of soil
sampling, temperature reading, or other items desired.
CHARTING
Much ecological data can be expressed through various forms
of charting. Where this is possible, a good deal of data can be
gotten on a small space. While there are many forms of charting,
only a few will be mentioned here. The teacher or student is ex-
pected to develop others for particular purposes.
Charting for various climatic functions such as temperatures,
pressure, and rainfall is universally used. Lines are used in
charting temperature and pressure, while precipitation is repre-
60
FIELD MANUAL OF PLANT ECOLOGY
80°F
70
60
50
40
30
20
III 1 1 Mil II
M A M J
SON
Fig. 8. Average temperature by months in degrees Fahrenheit and average rainfall
by months in inches for Manhattan, Kansas.
(b)
Fig. 9. Wind roses for the month of January : (a) North Pacific Ocean in latitude
37°N, longitude 137°W. (6) Just off the coast of Leyte, Philippines, in the northeast
trade-wind belt. The length of the lines indicates the proportion of time in which
the wind blows from the direction indicated.
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY
61
sented by columns (Fig. 8) and the proportion of the time the wind
comes from the various directions by wind roses (Fig. 9) .
Flower Charts. On a chart expressing the months, the time
of flowering may be indicated by a heavy line for each of as many
different plants as desired. If the plant has a long initial period
before a peak blossoming, the heavy line may gradually widen
Carex lasiocarpa
High Bog Shrub
Thuja
Fig. 10. A succession diagram of a northern Michigan bog.
of succession from one association to another.
Arrows show direction
to a maximum and then break away gradually or suddenly as the
facts indicate.
Succession Charts. This is one of the best ways of showing
them. It may be done in different ways. In setting up a sue-
62
FIELD MANUAL OF PLANT ECOLOGY
cession chart, one may take all of the associations involved or
pick out the important ones. In either case the names of the as-
sociations may be typed on a thin piece of cardboard which can
then be cut out. The names may then be arranged on a sheet,
the size determined by the exigencies of the situation, so that the
connecting lines will be as free from crossing one another as is
possible. If associations of different importance are used, the
more important may be in capital letters or in larger type
if printing is employed. Arrows connecting observed succes-
sion will build up the chart. Whether the climax association
Fig. 11. Diagram showing overlapping ranges for five species. The angles of the
lines differ from each other by 72 degrees.
should be at the top of the page, the center, or the bottom are
points of individual preference, as a rule. Since we usually read
down, many succession charts have the initial conditions at the
top. The width of the stems of the arrows connecting the names
of the associations gives an indication of the frequency of that suc-
cession (Fig. 10).
As a method of taking notes, the charting of observed suc-
cessions is very handy and a good deal of information can be
expressed in a very short time.
TO SHOW OVERLAPPING RANGES
It is often desirable to show ranges of plants which overlap
and consequently make the use of colors or shades too confusing.
A simple method of getting around this is to outline in turn the
ranges of the plants considered, then to put in parallel lines in
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 63
accordance with radiation diagrams previously set up. The num-
ber of ranges that may be shown is considerable, if mathemati-
cal accuracy in drawing is maintained. If, as in Fig. 11, five
plants are shown, the lines will be 72 degrees apart from each
other.
Additional examples of this method are illustrated by figures
on pages 378 and 379 of the ninth volume of the Botanical Re-
view, 1943.
POLYGONAL EXPRESSION OF DATA: POLYGRAPH1
While data may be expressed in the form of graphs for each
item, often it is distinctly advantageous to concentrate some of
the data in a more concise kind of expression, of which polygonal
expression is one useful type. As many radii equidistant from
each other as are needed are drawn from a point. Scales or parts
of scales, each suitable to the material for a given radius, are then
arbitrarily chosen and the values in question are then marked
on the proper radius. A line connecting these points constitutes
the polygon. If a series of diagrams is used, the same scale in
the same position must be used to permit comparison (Fig. 12).
Each radius may be used for some function of ecological work.
If climatological data are to be expressed, one radius may give
the average temperature for whatever period is selected, a second
radius may give the maximum in the period, a third the minimum,
a fourth may give the variability, a fifth may give the rainfall,
a sixth the maximum rainfall in one day, and so on. Such polyg-
onal graphs may be set up for each month, year, or whatever
period is desired. They may be interpreted by inspection and
will be very satisfactory where more than three items are to be
expressed at one time. In the Bulletin of the Torrey Botanical
Club (69:647-660. 1942) Oosting and Reed show by such graphs
the establishment of a white-birch community on cutover pulp-
wood land in northwest Maine. They have used four radii to
indicate percentage of dominant abundance, percentage of fre-
quency, percentage of total size of the classes represented, and
percentage of total dominant basal area, with the center zero of
each characteristic. With this method of expression, very neat
figures may be set up. The disadvantage sometimes is that size
1 Cf. Weaver and Clements, op. cit, pp. 35-36, after Lutz.
64
FIELD MANUAL OF PLANT ECOLOGY
may require too small a scale for fine distinctions, but the advan-
tage of correlating different things in one small diagram may
outweigh this. Another disadvantage may be the inclination to
put too many data into one figure. This makes the printing too
fine unless it is done on quite a large scale.
Fig. 12. Polygraphs. Two locations, one expressed by continuous line, the other
by dashes, showing differences in each of four characteristics on four different radii:
T, temperature in degrees Fahrenheit; P, precipitation in inches; F, percentage of
plants in flower; and W, percentage of the time that the wind is in the northwest.
Exercise 27. Charting
Chart data obtained in classwork or suggested by the instruc-
tor in one or another of the forms indicated above.
Repeat in connection with other exercises or as an exercise in
itself.
COMPARISON OF EVALUATION SCALES
It is frequently necessary tp choose between expressing cer-
tain data numerically or by common descriptive terms and to
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 65
change from one to the other. Where possible it is desirable to
set up a scale of units and express the points directly. This is
particularly so in evaluating frequency. One plant that is reck-
oned abundant will have a frequency of 95, another 80, etc.,
differences which the term " abundant" fails to bring out.
In view of the fact that terms are used more commonly, ef-
forts to evaluate them are worthy of consideration. Whether a
scale of 1 to 5 is better than 1 to 10 is a question depending
on the data in which one is interested. On a 1 to 5 scale, one
can use a series of terms which are rather well understood as
follows :
/ 0 — absent
1 — rare
/ 2 — scarce
3 — common
4 — abundant
5 — very abundant
If finer divisions or categories are desired, it is better to express
them numerically.
UNEQUAL SCALES FOR RATING SPECIES
IN COMMUNITIES
While most people are content to use such terms as rare, scarce,
common, abundant, etc., it is often desirable to be able to ex-
press such ideas in figures. To this problem A. G. Vestal has given
considerable attention.1 Since we employ the decimal scale for
many purposes, that scale would seem to give satisfactory re-
sults; however, decimal scales may be set up on different bases.
The units between may be the same throughout or they may them-
selves follow a pattern. A class exercise might be set up which
would enable the students to figure out a suitable pattern for
themselves. Where unequal scales are used, the first principle is
that the greatest inequality should be toward the lower end of
the scale and diminish to the upper end of the scale. One such
scale is as follows :
1 Vestal, A. G., "Unequal scales for rating species in communities," Amer.
Jour. BoL, 30:305-310. 1943.
66
FIELD MANUAL OF PLANT ECOLOGY
Scale
Difference
Percentages
Scale
Difference
Percentages
1
2
3
4
5
2.5
3.7
5
6.4
8
97.5-100
93.8-97.4
88.8-93.7
82.4-88.7
74.4-82.3
6
7
8
9
10
9.9
11.9
14.4
17.3
20.9
64.5-74.3
52.6-64.4
38.2-52.5
20.9-38.1
0-20.8
If this scale gives too fine a difference, scales of five units are
often advantageous. One which has been satisfactory from this
standpoint is given below.
Scale
Difference
Percentages
1
6
94-100
2
11
83-93
3
18
65-82
4
26
39-64
5
38
0-38
For other purposes other rates of inequality may be set up.
Similar results may be obtained by the use of semilogarithm
paper.
AQUATIC SITUATION
The following is a brief outline of the field, an important part
of field ecology.
I. Type of Body of Water.
A. Oceanography — oceans and seas (beyond the scope of
beginning classwork, as a rule).
B. Limnology [that part of ecology which deals with inland
waters — see " Limnology" by Paul S. Welch (Mc-
Graw-Hill Book Company. 1935) and " Limnological
Methods" by the same author (The Blakiston Com-
pany. 1948)].
a. Lentic (standing-water series).
(1) Lakes (fresh or salt).
(2) Small lakes, ponds, boglakes.
(3) Artificial lakes.
&. Lotic (running-water series).
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 67
(1) Streams, rivers, creeks; permanent, temporary,
and artificial.
(2) Springs.
(3) Hot springs.
II. Study.
A. Factors.
a. Physical.
(1) Depths.
(2) Temperature.
(3) Waves and wind.
(4) Turbidity and inherent color.
(5) Flow curves.
(6) Icework.
b. Chemical.
(1) Dissolved oxygen.
(2) Free C02.
(3) Hydrogen-ion concentration, pH.
(4) Monocarbonates.
(5) Dicarbonates.
c. Biotic.
(1) Plants.
(2) Animals.
III. Vegetation.
A. Recognition of communities.
B. Individual study of communities.
a. Quadrat studies.
b. Transect studies and profiles.
c. Individual plants — root systems, depth of water, etc.
C. Swamp, marsh, and bog.
D. Change to land.
a. Abrupt.
b. Succession.
E. Alternation.
F. Zonation.
IV. Experimentation: Artificial Vegetation, Etc.
Where aquatic areas are studied ecologically one may employ
the same general procedures as are utilized on land areas, with
suitable modification when necessary.
68 FIELD MANUAL OF PLANT ECOLOGY
ROOT SYSTEMS OF AQUATIC PLANTS
An outstanding feature of aquatic plants is the development
of the root system. This fact, combined with the relative ease
of excavating the major part of the root system, in case the water
is not too deep, makes the study of root systems an important
feature of aquatics. Under aquatic conditions one is likely to
find two types of roots. These are known as the feeding roots
and the anchoring roots. While all of the roots can absorb water
and minerals and serve in some degree for anchorage, it is quite
common to find early roots growing directly down and being rather
spongy in texture for a while. At some stage in their downward
development they contract, which has the effect of pulling the
rhizome down into the mud and thus firmly anchoring it. Some
feeding roots may branch from contractile roots, but in general
feeding roots arise from the rhizome and branch not far from it,
making a dense growth in the upper layers of the mud or sand
under the water.
Different plants may be dug up by members of the class.
The roots should be kept wet until the study is completed. Draw-
ings or photographs may be made on which later comparisons
may be based. (Cf. Sherff, Earl E., "The vegetation of Skokie
Marsh, with special reference to subterranean organs and their
interrelations," Bot. Gaz., 53:415-435. 1912.) A knowledge of
the root system explains the resistance of certain aquatic plants
to disruptive features of the environment. If the same spe-
cies of plants grows in different types of bottom, such as sand
and clay, a contrast between the root systems may be brought
out.
Exercise 28. Root Systems of Aquatic Plants
Dig up half a dozen or more important aquatic species. Study.
Sketch or photograph. Correlate with position in environment
by making a trench through the area of aquatic plants. Care-
fully tease out the roots of the plants and sketch at the proper
level on cross-ruled paper. In case of muddy water in the trench
a sufficient vertical section of the soil and root mass should be
laid out on dry ground and studied. „
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 69
DEPTH OF WATER IN WHICH AQUATIC PLANTS ARE GROWING
Particularly in working with aquatic situations it is often
desirable to know the depth of water through which the aquatic
plants will grow. Efforts to ascertain the greatest, least and aver-
age depth at which such plants may grow involves many measure-
ments. If the water is not too deep, measurement may be made
with measuring sticks graduated to meters and tenths. As many
measurements as possible should be made within the time allowed.
Sticks more than 3 meters long are too unwieldy for convenient
use. Waxed rope in which threads have been inserted or on which
markers have been painted may be used to suspend a weight.
Consideration of the type of bottom under the water needs to be
made, especially where there is fine muck or a false bottom.
Depth in bogs filled with peat is best determined with steel rods
such as are used with the Davis type of peat borer. More special
cases require more formidable gear such as that developed by
Ira Wilson1 or by well diggers.
A complete study may be made for the different kinds of
plants, both to determine the maximum depth in which they
grow and, if a species continues up on shore, how far above the
water table the plants will grow.
Exercise 29. Depth of Water
By measuring down from the surface of the water, determine
the greatest and least depth at which certain plants are growing
in the lake or river under consideration. Organize a diagram to
show the greatest and the least depths at which the various
species will grow.
Repeat in other water areas and compare.
PHYSICAL FEATURES OF THE WATER
The temperatures at various depths may be determined with
special thermometers made so that the reading is held until a
new set is made after being brought to the surface (Nagretti and
Zambra thermometer) or by an electric setup.
1 Wilson, Ira T., "A new device for sampling lake sediments," Sedimentary
Petrology, 11:73-79. 1941,
70 FIELD MANUAL OF PLANT ECOLOGY
The turbidity or light penetration is taken by the use of a
Secchi disk.
The mechanics of stream flow, wind and wave work, erosion,
and ice work offer many problems in physics. Their effects on
both plants as individuals and on vegetation are often quite con-
spicuous.
If good examples are available such exercises as follow may be
set up.
Exercise 30. Lake Study
Contrast the various shores of a lake with respect to the fol-
lowing:
Amount of wave and ice work.
Position with respect to prevailing wind.
Width of strand.
Character of the shore: rocky, sandy, marly, etc.
Erosion.
Kind and amount of vegetation in the water-land ecotone,
shown by transects taken from water to land (Exercises
23 to 25).
Associations, alternations, successional relationships. Com-
pare with those found in streams (Exercise 31) and bog-
lakes (Exercise 32).
Exercise 31. Stream Study
Contrast various parts of streams: shore, bottom, outer and
inner parts of curves, pools, rapids, and waterfalls with respect
to the following:
Wave action.
Flow effects — in other words, water erosion.
Kind and amount of vegetation in the water and along the
shore under these various conditions. Take transects.
Note associations, alternations, successional relationships,
and compare with those of lakes.
Exercise 32. Boglake Study
Contrast boglakes, with and without wave action, with or-
dinary lakes and with streams, in regard to the following:
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 71
Physical, biotic, and chemical factors.
Development of a floating mat.
Amount of organic accumulation.
Associations, successional relationships.
WATER CONSTITUENTS
Various substances are dissolved in the waters of streams and
lakes. Through chemical analysis in the laboratory of samples
taken in the field, the kinds and quantities of such solutes may be
established. The more commonly determined include dissolved
oxygen, free carbon dioxide, hydrogen-ion concentration (pH),
monocarbonates, and dicarbonates. (For pH see also Exercise
45.)
Exercise 33. Water Constituents
As opportunity offers and material is available, determine
some of the constituents of water as noted above.
It may be feasible to determine water constituents above and
below sewage outlets or above and below outlets of industrial
plants. Study the effects on plants, if present in the water and
along the shore.
CHARACTER OF THE BOTTOM
Specialized dredges are used to bring up known quantities of
bottom. The samples are then studied in the laboratory from
various standpoints. (See Welch, " Limnology," pp. 25-28.)
Exercise 34. Bottom Samples
As opportunity offers and material is available study the phys-
ical, chemical, and biotic constitution of samples of the bottom
of lakes, streams, and boglakes.
ZONATION1
The study of zonation or the development of belts of vege-
tation along a river or around lakes or ponds is always instruc-
tive. In such a study one or another of the transect methods is
1 Cf. Weaver and Clements, op. cit., pp. 6-7.
72 FIELD MANUAL OF PLANT ECOLOGY
most satisfactory. A map showing the various zones in the area
is a good way of expressing the results. This should be supple-
mented by a study of the physical factors using the proper meth-
ods for each.
If a long time is available, mass operations such as moving
blocks of sod containing land plants into various depths of water
may be carried on and studies made of the dying out or possible
rooting and development of any plants in the original block.
A study of variations from week to week, month to month,
or year to year in the water level, particularly of lakes, is always
an interesting one where it can be carried on. The reactions that
take place in the vegetation along the shore are sometimes con-
spicuous.1
Exercise 35. Zonation
Along a stream or around a lake or pond identify the zones of
vegetation. If a base map of the area is available, sketch in the
different zones. In the absence of a base map, first make a map,
then locate the different zones on it. Take transects, both line
and associational, in a suitable number of places from the water
up into the upland vegetation. Locate these on the map and let
them help determine the proper location of the different types of
vegetation.
ALTERNATION2
In the course of studying zonation, different plant groupings
may be found in the same relative position in the sere from water
to land. This phenomenon is known as alternation. It is more
frequent along rivers than around lakes. To ascertain whether
it is purely alternation or whether there is a successional rela-
tionship between the groupings requires the study of several oc-
currences of both in the same area.
1 In one case investigated at the University of Michigan Biological Station
the relationship between the level of the water and the average temperature for July
was established for the blossoming of Utricularia reswpinata in the Douglas Lake
region. It required both low water and a July temperature distinctly above the
normal average for this Utricularia to flower. Gates, F. C, "Conditions for the
flowering of Utricularia resupinata," Lilloa, 5:159-162. 1939.
2 Cf. Weaver and Clements, op. cit., pp. 7-9.
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 73
Exercise 36. Alternation
Include, if possible, examples of alternation on your map of
zonation, using different shading, or different markings of the same
color.
FACTORS OF HABITAT
INTRODUCTORY TO FACTORS
Various factors of the environment affect the plants in vege-
tation. The single or occasional determination that a class may
make of the factors of the environment will illustrate the method
but cannot furnish sufficient data for a complete study.
One should guard against too much study with instruments
at the expense of studying the plants themselves. For many
factors a single determination has but little value and yet that
single determination is all that the class may be able to make.
Averages of factors as measured by weather-bureau stations may
be obtained from weather-bureau figures, but it is wise to re-
member that the actual weather-bureau figures are not obtained
in the exact field which the class has under consideration. In
addition one should remember that plants undergo the extremes
as well as the means and the former are more likely to be dis-
astrous. Measurement of the following factors is usually most
valuable : heat (temperature) , precipitation, humidity, light, wind,
evaporation, soil composition, and soil water content, each of
which will be considered in an exercise following.
TEMPERATURE1
The measurement of heat is important in ecology, not only
tdexpress present temperature, but also to express climate. The
temperature of many things may be determined, but that of the
air and of the soil are those most frequently sought. For most
of these measurements ordinary thermometers are used. The
reading is made while the thermometer is immersed in the place
or medium whose temperature is required. To obtain climatic
data recording thermometers of various types may be employed.
1 Cf. also Weaver and Clements, op. tit., pp. 356-379; Braun-Blanquet, op. tit.
(tr. and rev. by Fuller and Conard), pp. 83-97.
74
FIELD MANUAL OF PLANT ECOLOGY
The simplest are those in which two metals are welded together,
the unequal expansion and contraction of which operate levers
which move a marker in contact with a revolving drum carry-
ing specially ruled paper. Electrical instruments may also be
used for ecological work in the field. The commonest figures
sought are the temperature of the air, the temperature of the wet
bulb, and the temperature of the soil at different depths. Ex-
Fig. 13. Thermocouple setup (not according to scale). Two kinds of wire, iron,
/, and constantan, C, are fused together at the ends. One fused end is maintained
in cracked ice in a thermos bottle, the other is set in a cork at the end of one tine of
a pair of pincers. The other tine is capped with a similar piece of cork. A gal-
vanometer, G, and a key, K, are included in the circuit. Shown also is a portion
of a leaf, L, whose temperature is to be taken when the other end of the fused wires
is imbedded in the mesophyll.
pression of climatological data involves a daily record so that aver-
ages may be obtained. In such cases, the average maximum and
the average minimum, from which the mean is calculated, are
the usual figures recorded, although they are not always the
most valuable from the standpoint of plants.
To obtain temperatures inside a plant, if the plant is suffi-
ciently large, a hole may be bored or an opening made and a ther-
mometer inserted into the tissue. Leaves may be rolled around
the bulb of a thermometer to obtain their temperature, being
careful not to allow the hand to influence the reading. To obtain
temperatures inside leaves and other parts of plants, the use of
a_ihermocouple is the most desirable method.. The thermo-
couple action results from the fact that when two different metals
are fused together at the ends and the ends are at different tern-
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 75
peratures, an electromotive force exists between the two metals.
By placing one set of fused ends in cracked ice in a Dewar bulb
or in a thermos flask, for constant temperature, and the other fused
end inside a leaf, a difference of potential is set up, which may
be evaluated on a sensitive galvanometer or potentiometer placed
in the circuit as shown in Fig. 13. Calibration of the system by
finding out the amount of deflection of the galvanometer needle
when known temperature differences are used makes it possible
to read leaf temperatures directly. Wires of iron and constantan
(60 per cent copper and 40 per cent nickel) make an excellent
pair to use for this purpose. For work with plants the exploring
end may be nearly as fine as a needle and be mounted in cork at
the end of one tine of a pair of forceps or pair of scissors, permit-
ting easy and rapid manipulation.
The temperature of the soil may be taken by digging a small
well to any desired depth and plunging a thermometer laterally
into the wall, or thermometers with different lengths of stem may
be employed. Regular soil thermometers are contained in a case
whose_steel-pointed end facilitates pushing them into the ground
to the proper depth. The reading is taken as soon as the mercury
becomes stationary.
In water various thermometers are used, one of which is the
Nagretti-Zambra thermometer, which is so made that it can be
put down to the desired depth, the reading established, and the
mercury column broken by inversion, then the thermometer
brought to the surface and read. Pulling an ordinary thermome-
ter up through water would change the reading unless the water
was of uniform temperature throughout.
Standard weather-bureau instruments exposed in standard
shelters include at least maximum and minimum thermometers.
Sun temperatures may be obtained from a black bulb in vacuo
which may be set up pointing to the North Pole (in the Northern
Hemisphere) in an area to which the sun has access throughout
the day.
Exercise 37. Heat Measurements
With the thermometers furnished, take temperatures as di-
rected of such things as the following:
76 FIELD MANUAL OF PLANT ECOLOGY
The air in the open and in shade, in crowns of plants.
The soil on the surface and at various depths.
Water of lakes, springs, streams; surface and at regular depths
to the bottom.
Soil of various colors in full sun and in shade.
Leaves under various conditions, by rolling them around the
bulb of the thermometer, taking care not to let the warmth of the
hand interfere.
If time permits, sufficient readings may be taken to permit
at least some evaluation of the micrometeorology as distinct
from the standard Weather Bureau records of the nearest sta-
tion.
PRECIPITATION1
The amount of precipitation, whether in the form of rain _or
snow, is of great importance to plants. For ordinary ecological
field work it is not usually feasible to obtain the records from given
spots in the field for a long time. It has been customary, there-
fore, to take weather-bureau figures from an adjacent town if
that is possible, or to maintain weather-bureau instruments at a
base station, using those records for the general averages of the
region. Admittedly, these are not the actual readings for the
spot worked. How far they depart is seldom known. It may be
considerable in instances.
The Weather Bureau uses an 8-inch metal gage in which to
collect rain; however, any sort of sharp-lipped container may be
used in the field. A funnel leading into a bottle is a simple-ar-
rangement. The neck of the bottle must be protected from re-
ceiving rain except through the funnel. To calibrate one must
know how much water in the bottle equals 1 inch of precipita-
tion. A graduated cylinder may then be used to make the meas-
urements, in hundredths of an inch or fractions of a millimeter.
Interesting experiments may involve the setting up of several
rain gages, some in the open and some under different types of
trees or other plants. In one such series Homer Jack (Ecology,
16:120-121. 1935) discovered that 0.12 of an inch of rain must
1 Cf. also Weaver and Clements, op. cit., pp. 210-214; Braun-Blanquet, op. cit.
(tr. and rev. by Fuller and Conard), pp. 111-125.
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 77
fall before any moisture gets to the ground through a mat of the
lichen, Cladonia.
Exercise 38. Precipitation
With the use of figures obtained by the class or data from a
regular or voluntary weather-bureau station, plot out the rain-
fall of the area in which the work is done.
RELATIVE HUMIDITY AND VAPOR-PRESSURE DEFICIT1
The relative humidity is the percentage of moisture actually
in the air at any given time compared to the total amount of
moisture that the air at that temperature is capable of holding.
The actual amount in the air is known as the absolute humidity
and may be determined by drawing air through gas chambers
containing chemicals to remove the moisture from the air. This
is seldom feasible in field work; however, the absolute humidity
may be calculated along with the relative humidity if the tem-
perature of the air and of a wet bulb be taken simultaneously. \
To do this an instrument known as a psychrometer may be made
by fixing two matched thermometers on a rack which may be
swung around in the air or set up on an egg-beater-like arrange-
ment and rotated in a small compass. If wind is present the ther-
mometers may remain stationary. The thermometers are placed
so that the bulb of one projects an inch or more below that of
the other. The lower one is covered with a jacket of linen tied
close to the bulb. Before using, this should be wet with dis-
tilled water and the whirling or twisting completed before the
linen dries out. In reading, one reads both thermometers at
short intervals while the cloth is still wet, until neither thermom-
eter changes in a period of 5 seconds. Reference to U.S. Weather
Bureau psychrometric tables then gives the relative humidity,
absolute humidity, dewpoints, etc. The greater^ the^ lowering
of the temperature of the wet bulb, the lower is the relative
humidity. The same number of degrees of lowering at high
temperatures, however, indicate a higher relative humidity than
1 Cf. Weaver and Clements, op. cit, pp. 333-346; Braun-Blanquet, op. cit.,
(tr. and rev. by Fuller and Canard), pp. 125-137.
78 FIELD MANUAL OF PLANT ECOLOGY
the same difference at lower temperatures, since the ability of
the air to hold moisture accelerates with increase in temperature.
Vapor-pressure Deficit. The vapor-pressure deficit is ex-
pressed in millimeters or in inches of mercury. It is the difference
between thej pressure exerted by the water vapor actually pres-
ent in the atmosphere at a given temperature and the pressure
exerted by the water vapor in a completely saturated atmos-
phere at that temperature.
The vapor-pressure deficit can also be calculated from the satu-
ration vapor pressure for the current dry-bulb temperature and the
saturation vapor pressure for the current dewpoint temperature.
The current dewpoint may be found in the U.S. Weather Bureau
psy chrome trie tables, if one knows the current wet- and dry-bulb
temperatures. Only if the temperature is the same do equal
values of relative humidity indicate equal vapor-pressure deficits.
Copyrighted nomograms (see page 117) permitting rapid deter-
minations of these values, once the wet- and dry-bulb tempera-
tures are known, are to be found in Ecology, 21:505-508, 1940.
If a series of relative humidity determinations are made, one
will generally find that there is a close relationship between the
temperature and the relative humidity, the latter sinking during
the day as the temperature rises. This is primarily because the
actual amount of water vapor in the air may remain essentially
the same irrespective of the temperature.
Exercise 39. Relative Humidity and Vapor-pressure Deficit
With a psychrometer obtain dry-bulb and wet-bulb tempera-
tures in different places and at different times of the day, as
directed. By reference to tables furnished give the relative hu-
midity, the absolute humidity, and the dewpoint temperature.
Calculate the vapor-pressure deficit.
LIGHT1
There is no perfect instrument to determine the exact amount
of light that plants actually use; consequently all light meters,
or photometers, that are used simply give relative values which
1 Weaver and Clements, op. cit., Chap. XIV; Braun-Blanquet, op. cit. (tr. and
rev. by Fuller and Conard), pp. 97-110.
DIRECTIONS FOR EXERCISES IN PLANT ECOLOGY 79
may be useful in so far as those figures are of value. Clements
used photographic paper which darkens to a given color in so
many seconds. The reading consists of counting the seconds
from the instant of exposure until the paper matches the color
of the standard alongside of it.
Such photometers as the McBeth Illuminator give the value
in foot-candles of the light from the standpoint of the instru-
ment. Readings may be made one after the other in different
habitats and the results recorded.
The photometers used by photographers may also be used to
make comparisons in light values.
Exercise 40. Light
With whatever instruments are available, determine the light
value by comparison with daylight in various situations.
WIND1
Generally speaking^ the det
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