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CORE LIST

■SDA Forest Service
Ksearch Paper RM-104

April 1973

ocky Mountain Forest and
ige Experiment Station

orest Service

I.S. Department of Agriculture
art Collins, Colorado

Estimating
Understory
Plant Cover With
Rated Microplots

by Meredith J. Morris

401784

Abstract

Plant cover measurements are used to detect changes caused
by grazing, fire, and other factors. Tests on both high and low
production sites of 17 areas in the West indicate that trained range
personnel rate small plots similarly in respect to the area occupied by
aerial and basal plant cover. Plots used ranged from 1/8 square inch
to 8 square inches. Equal area rectangles and circles were used. All
are well suited for rating plant cover, although the smaller sizes
tended to be slightly more precise.

Oxford: 268.5. Keywords: Range measurements, range
surveys, plant cover.

ACKNOWLEDGMENTS

Many individuals assisted in various
aspects of the microplot study. Without this
cooperation, the study would not have been
possible because nearly one-half million
samples were taken.

I am particularly grateful to Robert S.
Rummell for valuable assistance in the plan-
ning and conduct of this study and to Dr.
Richard S. Driscoll for much help in the
fieldwork. Forest Service personnel, past and
present, who did the sampling at two or more
locations were as follows: Robert F. Buttery,
John W. Chambers, Ralph K. Gierisch, Dr.
Frederick C. Hall, Irwin H. Johnson, Monty E.
Montague, Dr. Walter F. Mueggler, Thomas A.
Phillips, Cecil R. Sims, Philip R. South, Gerald
S. Strickler, Wayne H. Swenson, Stanton
Wallace, Andrew C. Wright, Dr. Henry A.
Wright, and Clerin W. Zumwalt.

Also, I wish to thank Glen E. Brink for
assistance in programing and data processing
and all the others who helped in this study.

USDA Forest Service April 1973

Research Paper RM-104 ~

Estimating Understory Plant Cover , -j

With Rated Microplots^ /^^J ^

Meredith J. Morris/Principal Biometrician
Rocky Mountain Forest and Range Experiment Station1

^Central headquarters maintained at Fort Collins, in cooperation with
Colorado State University.

Contents

Page

Previous Work 1

Procedures 2

Study Areas and Sampling Layout 2

Microplot Ratings 4

Point-Frame Readings 5

Data Analyses 5

Results and Discussion 6

Microplot Ratings 6

Point-Frame Readings 9

Efficiency 12

Conclusions 12

Literature Cited 12

Estimating Understory Plant Cover
With Rated Microplots

Meredith J. Morris

For some time, land managers on National
Forest and other publicly owned rangelands
have expressed a need for an indicator of how
influences such as livestock grazing, big game
use, recreation, and other environmental factors
are affecting the range. In my opinion, plant
cover — percent area occupied by shrubs, forbs,
and grasses — is the best single measure of these
impacts upon understory vegetation. Several
studies by other people and some preliminary
work of my own have shown that rating or
scoring the area occupied by plants inside small
plots, or "microplots," might be used to estimate
plant cover, both aerial and basal. If, in fact,
cover could be estimated accurately and
efficiently from rated microplots, then this
technique should be considered for general use
and for possible incorporation into the "3-Step
Method" for measuring trend in range condition
(Parker 1951). The plant cover index, as derived
in the 3-Step Method, is synonomous with the
frequency (of occurrence) figure long used by
plant ecologists. The plot used in the 3-Step
Method is much smaller than what is generally
used by ecologists, however.

Frequency is partially dependent upon
plant cover, so the two measures will be
correlated. The degree of correlation will depend
upon many factors, however. Hence, the value of
frequency as an index to plant cover will vary
from one set of conditions to another.

Previous Work

Although several authors pointed out that
plant density or cover indexes were larger than
estimates of plant cover obtained by methods
such as points or line intercept, they did not give
reasons for the difference. Hutchings and
Holmgren (1959) discussed the relation between
plant density index (frequency of aerial and
basal cover) and actual plant cover, as well as the
effects of plot size, number and size of plants,
plant dispersion, and plant shape on the index.
The overestimate of cover, or bias, obtained by
use of the loop as discussed by Hutchings and
Holmgren (1959) is actually identical to the bias
discussed by Goodall (1952) in relation to the
overestimation of cover with pins when the
points of the pins have greater than zero
dimension.

The idea of using rated plots for estimating
plant cover is not new. The use of a very small
plot, or "microplot," has been limited, however.

Hutchings and Holmgren (1959) summarized the
results of a test on synthetic plant populations
composed of 29/32-inch-diameter circles with
concentric 3/8-inch-diameter circles of different
colors randomly located on a strip of paper 2 feet
wide and 60 feet long. Several observers sampled
these synthetic populations with a 13/16-inch-
diameter loop at 1 -foot intervals along randomly
located 50-foot line transects. The loops were
rated to the nearest one-tenth of area occupied. A
large number of samples showed that the rated
loops provided close estimates of the actual area
occupied by the artificial populations of 3/8-inch
and 29/32-inch circles. Estimates were 1.2 and
1.1 times greater than the actual for the two
populations, respectively. Some of the
differences between the actual and observed
values could be attributed to sampling error,
however, as the rated loop estimates were quite
variable in these particular populations.

Cook and Box (1961) compared rated 3/4-
inch loops with point-frame and single point
readings for crown canopy and basal area along
100-foot transects in a mountain brush type in
northern Utah. For the loop, a measurement was
not recorded unless one-half or more of the loop
was filled; this constitutes a 2-point scale. Only
first contacts were recorded in aerial cover for all
three methods. They found that the rated loop
overestimated aerial cover for shrubby species
and underestimated it for grasses. Estimates of
aerial cover for forbs and basal area for all
groups were essentially the same by all three
methods.

Winkworth, Perry, and Rossetti (1962)
compared estimates from three sizes and shapes
of rated plots with those obtained from points
and line intercepts in an arid tussock grassland
in central Australia. The small plots used for
rating or scoring were a circle of 1.9 cm (0.75 inch)
diameter, and rectangles measuring 2 cm by 5 cm
and 4 cm by 10 cm. Presence or absence of aerial
cover in the circular plot was scored according to
whether cover was greater or less than 50
percent. The rectangular plots were scored in 10
percent cover classes from 0 to 100. A comparison
of means and variances showed that, while the
line intercept method was in doubt, for all
practical purposes the five methods gave similar
and equally reliable estimates. The point method
and the rated circular plot were more rapid than
the others.

In July 1962, a preliminary test of rated
microplots was conducted in the Fairfield
District of the Sawtooth National Forest in

Idaho. A meadow site and a bunchgrass site were
sampled with 25 randomly located points each.
Four rectangles and four circles of varying size,
fully described later in this report, were rated to
the nearest one-tenth of area occupied by shrub,
forb, and grass species for both aerial cover and
basal area. Litter, rock, bare soil, erosion
pavement, and mosses on the soil surface were
also rated. The same items rated on the
microplots were also recorded using a 10-point
frame at the same sample points.

Although the data were not completely
analyzed, summaries showed no apparent
differences in the ratings from the different
microplots. The point frame and the larger
microplots detected more species, however. It
was also noticed that some of the microplots were
easier to score than others.

Since the use of rated microplots seemed to
be feasible from the results of the preliminary

test, a large-scale study was designed with the
following objectives:

1. To determine the effect of selected microplot
sizes and shapes on ratings of cover or percent
area occupied by plants.

2. To estimate the optimum microplot on the
basis of a minimized variance-cost function.

3. To compare cover estimates derived from
rated microplots and pins in a point frame.

Procedures

Study Areas and Sampling Layout

The study was designed to sample the
major range types at 17 locations in the western
United States. These locations were selected
within National Forests and Experimental

Table 1. — Vegetation types, locations on Ranger Districts (RD) of National Forests (NF) and

Experimental Forests and Ranges, and sampling dates

Vegetation type

Location

Sampling date

Mountain grassland

Helena NF - Townsend RD, Townsend, Montana

June

1963

Mountain bunchgrass-Thurber fescue

Black Mesa Exp. Range, Crawford, Colorado

July

1964

Pacific bunchgrass

Sawtooth NF - Twin Falls RD, Twin Falls, Idaho

June

1963

Sod- forming grama

Sitgreaves NF - Pinedale RD,

October

1963

Snowflake, Arizona

Mixed gramas

Santa Rita Exp. Range, Amado, Arizona

October

1963

Mountain meadow

Beaverhead NF - Jackson RD, Jackson, Montana

July

1964

Mountain meadow

Tahoe NF - Sierraville RD,

August

1964

Sierraville, California

Upland herb-aspen

U.S. Sheep Station Exp. Range, Dubois, Idaho

August

1964

Sagebrush- grass

U.S. Sheep Station Exp. Range, Dubois, Idaho

June

1964

Chaparral

Prescott NF - Granite RD, Prescott , Arizona

April

1964

Mixed shrub

Roosevelt NF - Redfeather RD, September

1964

Redfeather Lakes, Colorado

Sagebrush-bitterbrush

Tahoe NF - Truckee RD, Truckee, California

August

1964

Pine-bunchgrass

Manitou Exp. Forest, Woodland Park, Colorado

August

1963

Pine-bunchgrass

Ochoco NF - Big Summit RD, Pineville, Oregon

June

1964

Pine-pinegrass

Starkey Exp. Range, LaGrande, Oregon

August

1963

Aspen-weed

Routt NF - Bears Ears RD, Craig, Colorado

July

1963

Annual grass

San Joaquin Exp. Range, Coarsegold, California

May

1964

Areas to represent most of the major range forage
types of the National Forests.

The range types and locations sampled
and sampling dates are shown in table 1. At each
location we selected two contrasting test sites,
one containing an abundance of vegetation and
a similar site containing a sparse amount (fig. 1).
The amount and homogeneity of the vegetation

on the two sites were the criteria for selection as
test areas.

The size of the sampling area varied from
about 1/2 acre minimum to about 5 acres
maximum. Fifty random sample points were
marked on each site (high and low), making a
total of 100 sample points for each location. Each
sample point was located by means of compass

Figure 1. — Two contrasting test
sites in the ponderosa pine-
bunchgrass type, Manitou
Experimental Forest, Colo-
rado:

bearings and pacing, and marked with an angle
iron stake with 3/4-inch flanges driven into the
ground to provide a fixed locus for the microplots
and point frame. All stakes were oriented so that
the open side of the "V" faced north. The
maximum height of the stakes aboveground was
about 5 1/2 feet; measurements were taken only
from the 4-foot level to the ground surface.

About 3 feet south of each metal stake, a
surveyor's wooden stake was driven into the
ground. Each wooden stake was numbered and
tagged for permanent identification so that
remeasurements could be made at a future time to
measure vegetative or site changes.

Microplot Ratings

Two microplot shapes (circles and
rectangles) with four sizes per shape were tested
(fig. 2). The circle has the least perimeter of any
geometric figure for a fixed area. The rectangle
was arbitrarily designed with the length being
twice the width. Each pair of shapes enclosed an
equal area, so that microplot shapes could be
directly compared. The areas in square inches
and the dimensions in inches for each microplot
size and shape were:

Circle

Rectangle

Area

(diameter)

1/4 x 1/2

0.125

0.3989

1/2 x 1

.500

.7979

1 x 2

2.000

1.5958

2x4

8.000

3.1915

Aerial or crown cover and basal area by
species for shrubs, forbs, grasses, and soil
surface items were rated at each sample point.
Items rated were defined as follows:

1. Aerial cover. — The vertical projection by
species of all live plant parts from the 4-foot
level to the ground surface.

2. Basal area. — The area occupied by live plant
parts at the ground surface, or the area defined
by live root crown. The basal area of plants
with basal rosettes was understood to be the
area defined by live root crowns only; the rest
of the live parts were considered aerial cover.

3. Litter. — Dead organic material lying on the
soil surface from previous years' growth. Dead
centers of plants were also considered as litter
if the parts were in contact with the ground
surface. Animal droppings were considered as
litter.

Figure 2. — Set of eight frames used in microplot study.
The largest rectangle is 2 by 4 inches.

4. Moss and lichens. — Area covered by moss
and lichens growing on the soil surface.

5. Bare soil. — All exposed mineral soil and rock
particles up to 1/8 inch diameter, and well-
dispersed rock particles up to 3/4 inch
diameter that did not provide a continuous
cover.

6. Erosion pavement. — Particles of rock from
1/8 to 3/4 inch in diameter forming a
continuous cover on the soil surface.
Individual rock particles from 1/8 to 3/4 inch
in diameter that did not form a continuous
cover were classified as bare soil.

7. Rock. — Stones larger than 3/4 inch in
diameter at the soil surface.

Two teams of two men each worked at each
site. One man on each team made the readings
for all eight of the microplots at all the sample
points in the site; the other man did all the
recording. Therefore, two complete sets of
readings were taken at each site. Forms were
designed for field use that would allow data to be
transferred directly to punch cards.

Sliding metal arms, which clamped se-
curely to the angle iron stake at a desired height,
were used to position the microplot frames in the
same place (fig. 3). The eight microplots were
rated, in random order, by each observer on each
team to the nearest one-tenth (1/10 = score of 1;
10/10 = score of 10) of area occupied, for each of
the items that occurred in that microplot. Only
one randomly selected microplot frame at a time
was used by each team until all the readings had
been made at all 50 sample points in the site.
Within each microplot, ratings of basal area and
soil surface items could have only a maximum
total of 10; the aerial cover ratings did not have
any combined maximum value.

Point-Frame Readings

After the ratings had been completed in a
site by each of the two observers for all eight
microplot frames, point readings from the 4-foot
level to the ground were taken by means of a cir-
cular point frame containing 10 vertical pins.
The point frame was designed so that the 10 pins
were equally spaced on a circle with a circumfer-
ence equal to that of the largest circular micro-
plot (fig. 4). All hits by species on live aerial parts
of plants and hits on basal area by species and
soil surface items were recorded. Only one set of
point readings was made on each site.

Time records were kept for each of the
microplots and the point-frame readings (that is,
for each set of 50 observations). When an
observer started rating one of the microplots at
the first sample point in a site, the recorder on the

Figure 3. — Sliding metal arm used to position
microplot frames in the same place.

team started a stopwatch. At the completion of
the last reading, the watch was stopped and the
total elapsed time recorded. The watch was
stopped during any interruptions. The time
involved in taking the point readings was
measured in a similar manner.

Data Analyses

Microplot and point-frame data were
analyzed in the following steps: (1) Identifying
and informative material such as plant species
names were edited and coded numerically; (2)
measurement and coded data were punched on
cards; (3) computer programs were written and
checked; and (4) detailed variance analyses were
computed.

Analyses of variance were made on the
aerial cover data with plot shape, plot size,
observers, sites, and locations being the main
effects. A plant species thus had to be present on
both sites within two or more locations. A
maximum of seven locations could be used in the
combined analysis because of storage
limitations in the computer. The analyses were
repeated for basal area ratings of each plant
species and ratings of ground surface items. A
mixed components-of-variance model was
assumed in this study, with microplot shape,
microplot size, and site being fixed effects and
observer and location being random effects. The
components of variance in this mixed model are
shown in table 2. Note that the main effects, A, B,
and D, and the interactions, AB, AD, BD, and
ABD, have no error terms for making
significance tests (F test). In these cases,
approximate tests were used (Cochran 1951,
Satterthwaite 1946).

Point-frame readings of aerial cover and
basal area of plant species and ground surface
items were summarized by observer, site, and
location, and compared directly with the largest
circular microplot ratings in analyses of
variance. Methods (points versus ratings of two
observers) and sites were assumed to be fixed
effects, and locations a random effect. The
components-of-variance model for this analysis
is shown in table 3.

Results and Discussion

Microplot Ratings

If the "best" microplot or plots were
determined for each plant species or soil surface
item, each cover type, each site, and each
location, it would be difficult to select the one
optimum microplot for management purposes.
Therefore, the microplot ratings were analyzed
for a particular plant species or soil surface item
and cover type occurring at two or more
locations. Note in table 2 that individual
observer, site, and location differences are
evaluated. Grasses, forbs, shrubs, and soil
surface items (different forms and shapes) were
all represented in the combined location
analyses.

Examples of combined location analyses
are shown in tables 4 and 5. Table 4 is the
analysis of variance for ratings of aerial cover of
Achillea lanulosa Nutt., or woolly yarrow. The
four locations are mountain bunchgrass-Thurber
fescue, upland herb-aspen, pine-bunchgrass, and
aspen-weed. Note that significant differences
were found between locations in the main effects
and in the interaction terms, shape-by-observer
and site-by-location. Since observer and location
effects are confounded (different observers were
used at different locations), the significant terms
are not important. And, of course, sites and

Table 2. — Components-of-variance model for microplot ratings — combined locations

Sbape

(a=2)

rbda2 „
ACE

rbcda2
AE

rbdea2
AC

rbcdea2
A

Size

(b=4)

rada2 „
BCE

racda2
BE

radea2
BC

racdea2
B

Observer

(c=2)

rabda2
CE

rabdea2
C

Site

(d=2)

raba2 „
CDE

rabca2
DE

rabea2
CD

rabcea2
D

Location

(e=2,3, .

rabda2
CE

rabcda2
E

. a2

rda2
ABCE

rcda2 _
ABE

rdea2
ABC

rcdea2
AB

rbda2 „
ACE

rbdea2
AC

radaBCE

radea2c

ABC

rdalBCE

rdeCTlBC

rbalcDE

rbcaADE

rbe°lcD

rbceaAD

raaBCDE

racaBDE

r3eaBCD

racea2D

ABD

ra2
ABCDE

rCCTABDE

reaiBCD

rceCTlBD

CD
ACD
BCD
ABCD
AE
BE
ABE
CE
ACE
BCE
ABCE
DE
ADE
BDE
ABDE
CDE
ACDE
BCDE
ABCDE
Residual

(r=50)

raba

CDE

+ rabea

rba

raa

ACDE

BCDE

+ rbea

+ raea

ACD

BCD

ABCDE
rbdalcE
rad0BCE

+ rea

ABCD

+ rbcda

+ racda

rda

ABCE

+ rcda

ABE

a2 + rabda£E

°2 + rbdalcE
°2 + radaBCE
°2 + rd°ABCE
°2 + rabaCDE
°Z + rbalcDE
°2 + ra°BCDE
°Z + r°ABCDE
°2 + rabaCDE
°2 + rbalcDE
°2 + raaBCDE
°2 + ralBCDE

+ rabca

+ rbca

+ raca

ADE
BDE

+ rca

ABDE

Table 3. — Components-of-variance model for point-frame readings versus
largest circular microplot ratings — combined locations

Method

A (a=3)

+ rbaAC

+ rbca^

Site

B (b=2)

+ raCTBC

+ raca*

Location

C Cc=2,3,

. . . ,

+ raba*

+ raABC

+ rCOAB

+ rbalc

+ ra°BC

ABC

+ rCTABC

Residual

(r=50)

Table 4.—

-Analysis of

variance for microplot

Table

5.-

-Analysis of variance for microplot

ratings of

aerial cover of

Achillea

ratings

of bare

soil at six

loca-

lanulosa at

four locations

tions

Source

of Degrees of Sum of

Mean

Source

of Degrees of

oUTn o r

Mean

variation freedom squares

o UUd L Co

variation freedom

q n ii a r"p q

squares

Shape

0. 744

0.744

Shape

f A")

17.7

17. 7

Size

(B) 3

8.36

2.79

Size

(B)

19.1

6.36

Observer

0.620

Observer

(C)

1.98

Site

(D) 1

68.3

Site

(D)

6540.0

Location

(E) 3

119.0

39.6

Location

(E)

11200.0

2250.0

0.594

0.198

12.0

3.99

0.439

0. 439

3. 30

3.30

4.47

1.49

32.2

10.7

ABC

0.447

0.149

ABC

6.31

2.10

0.263

0.220

5.56

1.85

3.26

1.09

ABD

0.0355

0.0118

ABD

1.80

0.599

1.41

1.60

ACD

0.000156

ACD

0.00667

BCD

3.51

1.17

BCD

5.39

1.80

ABCD

0.325

0.108

ABCD

10.4

3.47

0.0817

0.0272

18.6

3.72

17.2

1.91

36.7

2.45

ABE

1.47

0.164

ABE

31.0

2.07

2.76

0.920

199.0

39.9

ACE

0.0367

0.0122

ACE

54.7

10.9

BCE

10.1

1.13

BCE

57.6

3.84

ABCE

1.58

.176

ABCE

43.4

2.89

320.0

107.0

3520.0

704.0

ADE

0.653

0.218

ADE

16.9

3.38

BDE

26.6

2.96

BDE

137.0

9.16

ABDE

1.31

0.146

ABDE

18.0

1.20

CDE

0.590

0.197

CDE

124.0

24.8

ACDE

1.24

0.415

ACDE

12.5

2.50

BCDE

12.1

1. 35

BCDE

74.7

4.98

ABCDE

0.601

0.0668

ABCDE

49.8

3.32

Residual

6262

5540.0

0.884

Residual

9408

58700.0

6.24

Total

6399

6150.0

Total

9599

81000.0

** - Significant at the 0.01 probability level. ** - Significant at the 0.01 probability level.

locations were selected to be different. The mean
cover estimates of the eight microplots
corresponding to the analysis in table 4 were:

Mean cover

Size Rectangle Circle

1 0.314 0.320

2 .242 .228

3 .251 .206

4 .254 .221
Mean .265 .244

Size 1 is the smallest plot, and size 4 is the
largest.

Table 5 is the analysis of variance for
ratings of bare soil at six combined locations —
mountain grassland, mountain bunchgrass-
Thurber fescue, upland herb-aspen, pine-
bunchgrass, pine-pinegrass, and aspen-weed.
Significant differences were found between sites
and locations in the main effects and in the
interaction terms, observer-by-location, site-by-
location, and observer-by-site-by-location. The
mean cover estimates of the eight microplots
corresponding to the analysis in table 5 were:

Mean cover

Size

Rectangle

Circle

1.65

1.77

1.67

1.84

1.68

1.75

1.83

1.81

Mean

1.71

1.79

There were 22 analyses of the combined
locations type for aerial cover of different plant
species, and 20 analyses for basal area of plant
species and soil surface items. The same pattern
developed throughout all these analyses:
differences in the main effects, except for site
and location, were almost all nonsignificant. On
a very broad basis, then, we can say that
differences in microplot shape, microplot size,
and observers are nonsignificant statistically
for the populations studied. First-order
interaction terms that were significant mostly
involved site or location differences.

Point-Frame Readings

The ratings from the largest circular
microplot (about 3.2-inch diameter) and the
point-frame readings are compared statistically
in table 6. This table is the analysis of variance
for bare soil at the same six locations that are
combined in table 5. Mean ratings of each of two

Table 6. — Analysis of variance for methods com-
parison of bare soil readings at six
locations (largest circular microplot
versus point frame)

Source of
variation

Degrees of
freedom

Sum of
squares

Mean
squares

Method (A)

27.1

13.5

Site (B)

1250.0

T nrafinn ( C^S

LiULaUXUll \\s J

1820.0

363.0

3.64

1.82

89.3

8.93

571.0

114.0

ABC

40.4

4.04

Residual

1764

7870.0

4.46

Total

1799

11700.0

* - Significant at the 0.05 probability level
** - Significant at the 0.01 probability level

observers are compared to point-frame readings
in table 6, hence the two degrees of freedom for
method.

For aerial cover, only one analysis out of
22 showed a significant difference (table 7). For
basal area and soil surface items, only two
analyses out of 19 showed significant differences
(table 8).

Point-frame readings were higher in
absolute value than the 3.2-inch plot ratings in
all but two cases for the aerial cover analyses
(table 7). This is to be expected, however, because
the vertical projection within a fixed plot
boundary will have a maximum value of 100
percent cover, while pin contacts can add up to
over 100 percent cover since each contact for a
species is recorded. Differences between the two
methods were with grass species.

For soil surface items and basal area of
plants, only 7 out of 19 analyses showed point-
frame readings to be higher in absolute value
than microplot ratings (table 8). Thus, there is a
tendency for the rated microplots to give
somewhat higher readings (12 out of 19) than the
point frame, indicating a small positive bias.
This bias is not considered to be important from
a practical standpoint, however.

Table 7. — Mean values for 3 . 2- inch-diameter plots and point frames, and
nearest plot means, sizes, and shapes for aerial cover

Nearest plot values

Species or soil item

Number of
locations

3 . z-incn
plot

Point
frame

Mean

Size and
shape1

Annual forbs

0.276

0.310

0.286

Kc.vu11.qjx lanuloAa

.221

.330

.320

KqohikJj, glauca

.363

.473

.365

kwt<i.vinaxjjx n.o&m.

.693

.735

.693

fHRQCUvia vAJtg-lniana

.138

.130

.128

bxtkyfwM tuxzcintkuM

.143

.220

.225

TaAa.xa.cum o^icJ-viat<i

.128

.110

.122

Annual grasses

.365

1.27

.673

kgn.opyn.on 6pi.caJum

.283

.603

.365

A. tnachycaalum

.123

.595

.175

BouteJLoua gfiaclt<J>

.518

.837

.580

CatamagtioAtAj) AubeAcanA

.418

1.14

.530

VeAchampA-La ca<Lt>pi£oi>a,

1.13

2.53

1.14

ToAtuca. <Lda.ko<int>-a>

.970

2.46

.970

KozZqjuxl cAAJstxtfa

.163

.320

.163

Poa & dC-undo.

.132

.367

.258

SyUja.vu.on. hy6t/vix

.128 *

.180

.192

Stlpa comata.

.030

.065

.060

CaJLdX spp.

1.11

1.19

1.18

hvtmUiia. ^njjgi.da.

.605

1.28

.633

A. tsU.de.vitata

.623

.873

.833

PuMkia tnJAzwbxta

.833

1.26

.833

* - Significantly different from points.

1 - R = rectangle, C = circle, 1 to 4 = smallest to largest size.

Table 8. — Mean values for 3. 2-inch-diameter plots and point frames, and nearest
plot means, sizes, and shapes for basal area and soil surface items

Species or soil item

locations

3 • 2— inch
plot

jr o mt
frame

Nearest
Mean

plot values
Size and
shape1

Bare soil2

1.81

1.56

1.65

Bare soil

3.06

2.80

2.99

Bare soil

2.83

2.34

2.46

Erosion pavement

.698

.442

.508

Erosion pavement

.829

.760

.788

Rock

.127

.150

.148

Rock

.422

.448

.446

Litter

7.02

7.41

7.47

Litter

4.56 *

5.59

5.28

Litter

5.51 *

6.05

Moss and lichens

.866

1.18

1.08

kQ06tnJj> gtauca

.102

.020

.025

1C , 2C

Ant&nncvuxi ko^qjx

.572

.125

.367

Agtiopynon &p<icatwm

.095

.077

.078

Bout&lotMi gfiacjJLLb

.162

.067

.082

FeAtuca -Ldahoe.n6<u>

.372

.337

.335

KoztwLa. cJu^tatR

.065

.040

Poa iexLunda.

.080

.120

.110

CaAtx spp.

.375

.020

.152

All too high

* - Significantly different from points.

- R = rectangle, C = circle, 1 to 4 = smallest to largest size.

- Some items separated because of storage limitations in computer.

Efficiency

The final step consisted of comparing the
efficiencies of the various microplots. Sur-
prisingly, the average time required to read the
four sizes of plots was about the same, although
there was considerable variation among in-
dividual plots because of differences in plant size
and form, community structure, and observers.
The mean times in minutes required for es-
timating the individual plots by all the observers
at all 17 locations were:

Mean times

Size Rectangle Circle

1 0.62 0.65

2 .67 .62

3 .71 .67

4 .80 .75
Mean .70 .67

Time increased gradually from the smallest to
the largest plots, but the differences are not
significant. The largest plots (2 -by 4-inch rec-
tangle and 3.2-inch diameter) do, however, take
enough more time to be excluded from considera-
tion on a practical basis. Plot variances were all
of about the same magnitude. The microplots
were about five times as efficient, timewise, as
the point frame.

Conclusions

The rated microplots used in this study are
precise, efficient, and accurate, particularly for
basal area and ground surface items. The
different analyses did not identify any one best
microplot or microplots for rating cover (objec-
tive 1), although the smaller, circular plots were
usually nearer to the point-frame readings in
absolute values (objective 3). Rated microplots
are much more efficient than the point method
from the standpoint of time involved in es-
timating cover, however. Moreover, the
microplots are all about the same in efficiency
(objective 2).

In general, the 1/2- by 1-inch rectangle is a
good compromise in overall performance,
although it has no great advantage over the 0.8-
jnch-diameter circle. Most of the people involved
in the study preferred a rectangular plot over a
circular one for rating, however, which tips the
scales somewhat in favor of the rectangular plot.
It is interesting to note that the 0.8-inch-diameter
plot used in this study is very near in size to the
3/4-inch loop presently used in the 3-Step
Method.

Rated plots will give a precise estimate of
plant cover, a population parameter that can be
defined specifically, whereas frequency depends
upon several attributes in a plant community.
Hence, frequency estimates are often difficult to
interpret. Thus rated plots could be of benefit
insofar as the existing loop method is concerned.

Literature Cited

Cochran, W. G.

1951. Testing a linear relation among
variances. Biometrics 7(1): 17-32.

Cook, C. Wayne, and Thadis W. Box.

1961. A comparison of the loop and point
methods of analyzing vegetation. J.
Range Manage. 14: 22-27.

Goodall, D. W.

1952. Some considerations in the use of point
quadrats for the analysis of vegetation.
Aust. J. Sci. Res. Ser. B 5 (1): 1-41.

Hutchings, Selar S., and Ralph C. Holmgren.
1959. Interpretation of loop-frequency data as a
measure of plant cover. Ecology 40: 668-
677.

Parker, Kenneth W.
1951. A method for measuring trend in range
condition on National Forest ranges. 26 p.
U.S. Dep. Agric, For. Serv., Wash., D.C.
Satterthwaite, F. E.
1946. An approximate distribution of estimates
of variance components. Biom. Bull. 2:
110-114.

Winkworth, R. E., R. A. Perry, and C. O. Rossetti.

1962. A comparison of methods of estimating
plant cover in an arid grassland
community. J. Range Manage. 15: 194-
196.

Agriculture-CSU, Ft. Collins

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