razing animals affect plants in several interrelated
ways. In addition to defoliating and trampling
plants, grazing animals affect the surrounding
soil by other mechanical means, such as breaking the soil
surface and transferring seed, and by removing and
redistributing nutrients through excreta. The effects of
grazing on a specific plant species or individual plants
depend not only on the plant’s palatability, the availabili-
ty of alternative plants, and site characteristics, but also
on grazing management. Grazing management factors,
including season of grazing, grazing pressure, length of
grazing period, and species and class of grazing animal,
can affect plants. Collecting data in a botanical survey to
help identify the effects of grazing management on plant
communities is essential for evaluating grazing impacts,
determining management considerations, and develop-
ing conservation plans.
Resource professionals must often survey specific
plant populations to collect data for the Endangered
Species Act, for mitigation and conservation plans, or for
other natural resource research. In a grazed ecosystem,
the resource professional should describe grazing man-
agement and utilization in addition to collecting data on
the targeted survey plant population(s). This publication
outlines the data needed to describe grazing manage-
ment and utilization. Steps 1 and 6 should be completed
and/or reviewed every time the plant population is sur-
veyed. Step 7, estimating residual dry matter, should be
done at the end of the grazing and growing season.
Guidelines for Describing Grazing Management and Utilization
when Conducting Botanical Surveys
SHEILA BARRY
University of California Cooperative Extension
Livestock/Natural Resource Advisor, Tehama, Glenn, and Colusa Counties
DESCRIBING GRAZING MANAGEMENT: STEPS 1–4
Step 1. Size of Grazing Unit (Form 1)
Determine the size of the grazing unit in which the sur-
veyed plant population is located. A grazing unit is typi-
cally defined by fencelines or other physical barriers.
Step 2. Season of Grazing (Form 1)
Record the dates that grazing unit was grazed. If the number,
species, or class of grazing animals varied during the grazing
season, record grazing dates for each variation. It will also be
helpful to indicate the amount and dates if supplemental for-
age or feed (hay, liquid, blocks) was fed.
Step 3. Animal Units in the Grazing Unit (Form 1)
Multiply the number of individuals for each species and
class in the grazing unit by the corresponding animal unit
equivalent (AUE) (table 1) to determine the animal units
(AU) by species and class. Total the AUE for each grazing
period.
Step 4. Grazing Pressure (Form 1)
Calculate the grazing pressure for each grazing period.
The grazing pressure is animal demand per unit area
during the grazing time period.
Form 1. Season of grazing and animal unit equivalents (AUE).
Grazing unit location:_____________________________________________________________ Acres:_________________________
Grazing period Grazing animals Supplement Grazing pressure
Date Date Species Class Number AUE value Total Type Amount (AU/acres)
on off (head) (table 1) AU
A B (A×B)
UNIVERSITY OF CALIFORNIA
Division of Agriculture and Natural Resources
Publication 7225
G
http://commserv.ucdavis.edu/freepub/
Form 2. Surveyed plant population utilization.
Plant population
Survey date Location Size (acres) Physiological stage Use class
Example: Field A, 800 acres, was grazed by 42 fall-calving cows/calves from November 1 to May 1. From November 1 to February 1
the cows were fed 10 pounds/head/day of alfalfa hay. From February 15 to May 1, 20 weaned lambs grazed with the cows/calves.
Trace mineral salt was available for the cows and sheep throughout the grazing season. Form 1 would be completed as follows:
Grazing unit location: Field A Acres: 800
Grazing period Grazing animals Supplement Grazing pressure
Date Date Species Class Number AUE value Total Type Amount (AU/acres)
on off (head) (table 1) AU
A B (A×B)
Nov. 1 Feb. 1 cattle cows/calves 42 1.0 42.0 alfalfa hay 10 lb/hd/day .053
mineral free choice
Feb. 1 Feb. 15 cattle cows/calves 42 1.0 42.0 mineral free choice .053
Feb. 15 May 1 cattle cows/calves 42 1.0 42.00 mineral free choice .056
sheep weaned lambs 20 0.14 2.80 mineral free choice
44.80
ESTIMATING THE UTILIZATION OF SURVEYED
PLANT POPULATION AND RESIDUAL DRY MATTER:
STEPS 5–7
Typically, estimates of vegetation utilization and residual
dry matter are determined for the entire grazing manage-
ment unit. Although information for the entire grazing
unit is invaluable, these guidelines recognize that profes-
sionals conducting botanical plant surveys for specific
species may not have the time or resources to monitor
extensive range sites. The following guidelines for esti-
mating vegetation utilization and residual dry matter,
therefore, apply specifically to the surveyed plant popu-
lation and the immediately surrounding site.
Step 5. Visual Utilization Estimate (Form 2)
The degree of utilization should be estimated for each
plant population surveyed. The estimate should be based
on use classes 1 to 5 as described in table 2. Record the
use class every time the population is surveyed and also
at the end of the grazing season. Whenever the use class
is recorded, note the physiological stage of the surveyed
plant. Some plants may be palatable early in the grazing
season but not later, or vice versa. The use class should
be estimated at the same sample points where botanical
Table 1. Animal unit equivalents (AUE) for various species
and classes.
Species and class AUE
Cattle
Mature bull 1.5
Mature cow or cow/calf pairs 1.0
Cow/calf pairs (calves over 6 months) 1.35
Stockers or yearlings (12–24 months) 0.8
Sheep
Ewe/lamb pair 0.3
Mature sheep, nonlactating 0.2
Weaned lambs 0.14
Others
Saddle horse 1.25
Deer, blacktail 0.2
Deer, mule 0.23
Elk 0.60
Adapted from Vallentine 1990.
2 • Guidelines for Describing Grazing Management and Utilization when Conducting Botanical Surveys
Form 3. Estimated residual dry matter (RDM).
Samples Dried weight (g) Pounds/acre
1 x 100 =
2 x 100 =
3 x 100 =
4 x 100 =
5 x 100 =
6 x 100 =
7 x 100 =
8 x 100 =
9 x 100 =
10 x 100 =
11 x 100 =
12 x 100 =
13 x 100 =
14 x 100 =
15 x 100 =
Note: If the standard deviation of these estimates is one-half or
larger than the average, more samples should be collected and
added to the average.
data are collected, and the survey method used should
also be noted.
Step 6. Utilization Mapping
Include a map of the grazing unit with the surveyed
plant population information. This map can help provide
information about livestock distribution and its effects on
plant communities. Factors in a grazing unit that influ-
ence livestock use should be present on the map, includ-
ing physical features, such as topography, water sources,
and soil and vegetation types (fig. 1), and fences, corrals,
gates, roads, and shade. Aerial photos may be a good
source of this information (see Nader et al. 1994).
Utilization data for surveyed plants (Step 5) should be
recorded on the grazing unit map. Residual dry matter
estimates (Step 7) may also be recorded on the map.
Step 7. Estimate Residual Dry Matter (Form 3)
Residual dry matter (RDM) is the amount of dried plant
material remaining above ground at the end of the grow-
ing season after the grazing period. RDM should be mea-
sured after the grazing and growing season. RDM
reduces soil erosion, enhances water retention, and
strengthens perennial plants. Suggested end-of-season
RDM levels vary depending on specific site factors.
RDM estimates can be obtained by clipping and
weighing, comparative yields, or visually by using photo
Figure 1. Sketch of grazing unit showing fences, gates, water,
map units or zones, and use class for surveyed plant popula-
tion. Map units or zones are determined based on topogra-
phy, roads, hills, trees, water, gates, etc. and reflect expected
differences in grazing use. Adapted from Nader et al. 1994.
Table 2. Determining use class for surveyed plant population.
Degree
Use class of use Description
1: None 0–15% Little or no use of surveyed species.
2: Light 16–35% Less than one-third of the surveyed
species shows evidence of being
grazed. Trampling damage is minimal.
3: Moderate 36–65% Grazing is spotty but evident (over
one-third of the surveyed species
shows evidence of being grazed).
Trampling damage may be evident.
4: Heavy 66–80% Surveyed species is closely cropped.
Trampling damage may be evident.
5: Severe Over 80% Surveyed species grubbed. Trampling
damage should be evident.
Note: If the surveyed species has a low-forage value, trampling dam-
age may be evident before the plants appear grazed. These observa-
tions should be recorded. Adapted from Anderson and Currier 1973.
standards or descriptions (see Clawson, McDougald, and
Duncan 1982). Clipping and weighing residual dry mat-
ter around the survey plant population should provide
the most accurate information for estimating residue veg-
etation level. To estimate RDM using the clip-and-weigh
method, collect 10 to 15 circular plot samples with an
area of 0.96 square feet each from within the survey area.
Guidelines for Describing Grazing Management and Utilization when Conducting Botanical Surveys • 3
REFERENCES
Anderson, E. W., and W. F. Currier. 1973. Evaluating
zones of utilization. J Range Mgmt 26(2):87–91.
Clawson, W. J., N. K. McDougald, and D. A. Duncan. 1982.
Guidelines for residue management on annual range.
Oakland: University of California Division of Agriculture
and Natural Resources, Leaflet 21327.
Nader, G. M., et al. 1994. How to monitor rangeland
resources. Oakland: University of California Division of
Agriculture and Natural Resources, Intermountain
Workgroup Publication 2.
Vallentine, J. F. 1990. Grazing management. San Diego:
Academic Press.
Locate sample sites by random selection. Toss a sample
hoop (see below) in a random direction or collect a sam-
ple every 5 or 10 paces.
A sample hoop enclosing an area of 0.96 square feet
can be constructed from a wire cable or other material
41.66 inches (105.82 cm) long. Each gram of RDM inside a
hoop whose area is 0.96 square feet represents 100
pounds per acre (112 kg/ha). Use hand shears to clip the
aboveground plant material very close to the ground,
leaving about 1⁄4 to 1⁄2 inch (6–12 mm) stubble height. Clip
all rooted plant material within the hoop. Avoid picking
up dirt, rocks, and other nonplant material. Place the
sample in a paper bag. The sample should be dried
before it is weighed. To dry the sample, place in a heated
environment for at least 24 hours. During this time, mois-
ture from the vegetation is lost by evaporation and the
plant material becomes is “air dried.” Weigh the sample
in grams (remember to subtract the weight of the bag
containing the sample).
CONCLUSION
Over time, plant population data collected by resource
professionals should indicate whether changes have
occurred and whether management practices should be
adjusted. Grazing management data as described here
will be key to helping land managers make these evalua-
tions and adjustments. Stocking rate, time and distribu-
tion of grazing, and species of grazing animal can be
adjusted to work toward the objective for the range site.
4 • Guidelines for Describing Grazing Management and Utilization when Conducting Botanical Surveys
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