Environmental Engineering Reference
In-Depth Information
5.3.11 Field Forms
Customized data sheets or files are frequently used in ecology to help streamline
data collection and ensure that nothing is accidentally omitted. Data sheets can be
as simple as a table on a single page (see Field Labs at the end of this chapter) to a
complex multi-page and attribute form like is used in wetland delineation. By
listing commonly-encountered plant species in the form in advance, then the data
recorder does not have to write them in each time data is collected. In addition, if
repeated sampling is planned, consistent data forms can ensure that the same data is
collected each time. These forms can also be designed to simplify data entry once
fieldwork is completed.
5.4 Basic Analysis Techniques Commonly Used
for Vegetation Data
As with sampling techniques, entire topics have been written about analyzing ecolog-
ical and vegetation data. The reader is encouraged to explore McCune and Grace
( 2002 ) and Kenkel ( 2006 ) for more detailed discussion of multivariate techniques,
their assumptions, and the data transformations needed to meet those assumptions.
5.4.1 Basic Calculations
Summarizing the basic attributes of a plant population or community is an impor-
tant step in the initial stages of data analysis. Exploratory data analysis is critical to
understanding the data structure in preparation for more advanced analyses (Kenkel
2006 ).
￿ Frequency: The number of plots or samples in which a species appears, based
upon presence or absence. Frequency is a good measure of how common the
species is across the site.
￿ Density: The number of individuals per area. Density measures can be quite
variable, spatially. Measures of mean and variability are calculated.
￿ Cover or Basal Area: The areal cover of a plant. Basal area pertains to tree
trunks, and is
2 2 where d is the diameter of the tree at breast height (typically
measured with a special diameter tape).
d
π
Relative values of each of these measures can be calculated, and these are how
much each species contributes (as a fraction or percent) of the total frequency,
density, or cover of all species. Calculating relative values enables comparisons
between sites with dramatically different total cover, for example.
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