Sampling Vegetation Attributes - Natural Resources Conservation ...
Sampling Vegetation Attributes - Natural Resources Conservation ...
Sampling Vegetation Attributes - Natural Resources Conservation ...
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II. INTRODUCTION<br />
INTRODUCTION<br />
Identifying the appropriate sampling technique first requires the identification of the proper<br />
vegetation characteristic or attribute to measure. To do this the examiner must consider<br />
objectives, life form (grass, forb, shrub, or tree), distribution patterns of individuals of a<br />
species, distribution patterns between species (community mosaic pattern), efficiency of data<br />
collection from an economic standpoint, and accuracy and precision of the data.<br />
Permittees, lessees, other rangeland users, and interested publics should be consulted and<br />
encouraged to participate in the collection and analysis of monitoring data. Those individuals<br />
or groups interested in helping to collect data should be trained in the technique used in the<br />
specific management unit.<br />
This document deals with the collection of vegetation data. The interpretation of that data<br />
will be addressed in other documents. This document does not address interpreting vegetation<br />
data for adjusting livestock numbers or making other management decisions.<br />
A. Terms and Concepts The following terms require an expanded discussion<br />
beyond the scope of the Glossary of Terms:<br />
1. Inventory Inventory is the systematic acquisition and analysis of information<br />
needed to describe, characterize, or quantify vegetation. As might be expected,<br />
data for many different vegetation attributes can be collected. Inventories can be<br />
used not only for mapping and describing ecological sites, but also for determining<br />
ecological status, assessing the distribution and abundance of species, and establishing<br />
baseline data for monitoring studies.<br />
2. Population A population (used here in the statistical, not the biological, sense)<br />
is a complete collection of objects (usually called units) about which one wishes to<br />
make statistical inferences. Population units can be individual plants, points, plots,<br />
quadrats, or transects.<br />
3. <strong>Sampling</strong> Unit A sampling unit is one of a set of objects in a sample that is<br />
drawn to make inferences about a population of those same objects. A collection<br />
of sampling units is a sample. <strong>Sampling</strong> units can be individual plants, points,<br />
plots, quadrats, or transects.<br />
4. Sample A sample is a set of units selected from a population used to estimate<br />
something about the population (statisticians call this making inference about the<br />
population). In order to properly make inferences about the population, the units<br />
must be selected using some random procedure (see Technical Reference, Measuring<br />
& Monitoring Plant Populations). The units selected are called sampling units.<br />
5. <strong>Sampling</strong> <strong>Sampling</strong> is a means by which inferences about a plant community<br />
can be made based on information from an examination of a small proportion of<br />
that community. The most complete way to determine the characteristics of a<br />
population is to conduct a complete enumeration or census. In a census, each<br />
individual unit in the population is sampled to provide the data for the aggregate.<br />
This process is both time-consuming and costly. It may also result in inaccurate<br />
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