| Measuring vegetation is one of the important
parts of rangeland monitoring, which records changes in resource
status to assess the land's response to a management program
at the site. Such changes can only be detected by a series
of
measurements spanning time. Data collected from a range inventory
provide a valuable baseline against which to compare responses,
but monitoring can rarely be conducted at the same level of
detail as the information provided by an inventory. Instead,
monitoring is usually based on observations of key areas and
key vegetation attributes carefully selected to meet the objectives
of the program. For example, species composition could be measured
in a riparian area to determine the impact of a certain grazing
system or ground cover could be chosen to monitor the impact
of tourism at a popular site in a National Park. |
Full image (60K)
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For this activity, we will monitor to determine cover,
frequency, and composition of the vegetation.
Choose a site that is easily accessible. If you have a Forest Service
site with previous data collected on vegetation, you can use that
to make comparisons. Quadrat size for sampling is 40 cm x 40 cm.
Quadrats are systematically placed along transects at paced intervals.
Instructions for Building the PVC Frame
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 |
Parts list for one frame
|
| Quantity |
Length |
Item |
Part |
| 4 |
36.2 cm |
1/2" Schedule 40 PVC Pipe |
upright stem and sides |
| 2 |
18.3 cm |
1/2" Schedule 40 PVC Pipe |
attach to tee |
| 1 |
12.0 cm |
1/2" Schedule 40 PVC Pipe |
handle |
| 1 |
|
1/2" PVC Elbow SS |
|
| 2 |
|
1/2" PVC Elbows ST |
|
| 1 |
|
1/2" PVC Tee STS |
|
| 4 |
|
1/2" PVC Male Adapters |
|
| 1 |
|
1/2" PVC Female Adapter |
|
| 3 |
|
1/2" PVC Caps S |
|
S = a slip fitting
T = a threaded fitting
An irrigation warehouse person can understand this parts list as
is.
200 feet of Schedule 40 PVC Pipe is enough for 30 frames.
Multiply the quantity of fittings by the number of frames for your
parts list.
In this activity, allow each student to collect data using PVC
frames. Instructor can collect sample data at site beforehand (200
frames) and compare with accuracy of data collected by students.
Cover
1. The first measurement is cover. Cover is one of the most commonly
measured attributes in range inventory and monitoring programs.
Many of the methods to determine cover can be conducted simply,
quickly, and with acceptable levels of accuracy and precision, making
it a favored attribute to survey large areas.
Measure Ground cover hits: the pointer in each quadrat
is used to record ground cover. Record the attribute that is "hit"
by the tip of the pointer. The pointer must "hit" a live
perennial (green) plant base to record a live plant base. Litter
is any dead, organic matter on the soil surface that is large enough
to be identified as litter when "hit" by the pointer.
Cover is the vertical projection of plant material onto the ground
when viewed from above. It is usually expressed as a percentage
value. For example, 18% cover indicates a birds-eye-view would reveal
18% of the surface area as vegetative material with the remaining
82% as bare ground. In some forestry situations cover is expressed
on an area basis, such as square meters/hectare or square feet/acre.
Cover can be measured for the entire vegetation in an area, or
can be applied to individual species. In many areas, overlapping
plants can mean more than one species contributes to cover. Decisions
involving which species to record depend upon the objectives of
the study, and should be clearly described as ground rules during
the planning stage. Usually, if ground cover is the attribute of
interest only the uppermost component is recorded, whereas basal
cover is identified by the species occurring at the soil surface.
Frequency
2. Measure Frequency: herbaceous plants (annual or perennial)
must be rooted in quadrat. Count annuals if dry or green if still
rooted in quadrat. Annuals are grouped only as grasses or forbs.
Shrubs are counted if rooted in quadrat or any woody part of plant
overhangs the quadrat. Record which species occur in the frame.
The number of occurrences divided by the total number of frames
is the frequency.
Frequency means the probability of finding a species within a particular
area. The probability is based on the occurrence of that species
in a series of sample units. For example, if a species has a frequency
of 75%, we expect it to occur in three out of every four quadrats
examined. Frequency is expressed as a value between 0% and 100%,
representing the proportion of quadrats where the particular species
was found during sampling. For example, if we observed 200 quadrats
and found the target species in 156 of those quadrats, frequency
would be 156/200 = 78%.
Frequency is a simple vegetation attribute to measure because it
only requires identification of the species in each quadrat, and
does not require that individuals are distinguished, measured, or
counted. Therefore, data collection is usually a more rapid procedure
than for other vegetation attributes such as biomass, cover, or
density, which involve counting or subjective quantification. This
advantage is most apparent in rangeland vegetation characterized
by a relatively low species richness, but diminishes in vegetation
with complex species composition.
Frequency values are determined for individual species because
an overall frequency for the entire vegetation cannot be obtained,
in contrast to other attributes such as biomass, cover, or density.
Likewise, it is not possible to obtain a meaningful expression of
species composition from frequency data because the absolute abundance
is not measured, only the presence of a species is measured.
Frequency can be a sensitive method to detect vegetation changes
at a site. Its ease and speed of data collection means that frequency
is suited to large areas, so it is sometimes adopted by State and
Federal agencies for descriptive rangeland inventory or monitoring
programs.
Species Composition
3. Species composition, a commonly determined attribute, refers
to the contribution of each plant species to the vegetation. Species
composition is generally expressed as a percent, so that all species
components add up to 100%. It can be expressed on either an individual
species basis, or by species groups that are defined according to
the objectives of the inventory or monitoring program (eg., Aristida
spp., perennial forage grasses, etc.). It is regarded as an important
indicator of ecological and management processes at a site.
To measure species composition, score the top three species
based on the amount of vegetaion (whether green or brown).
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