Environmental Engineering Reference
In-Depth Information
features, like access points, labeled permanent plot locations, streams, or
different plant community locations can be extremely helpful in the future,
or when sharing data collection duties with other workers. They also help ensure
that interpretations made in the field align with those assumed back in the lab or
stored in the computer file.
Multiple observers: If large amounts of data are collected, it is inevitable that
multiple personnel will be involved in vegetation assessment. Working with
multiple observers adds additional variation in (1) plot boundary decision
interpretation, (2) visual percent-cover estimates, and (3) definitions of
individuals, among other aspects. One way to minimize variability is to be
clear and consistent about rules and definitions, and document them in standard
operating procedures (SOPs). In order to minimize variability in cover estimates,
calibrating teams until results are consistent between observers is important
(Kercher et al.
2003
). This calibration may have to be repeated on a daily
basis. Different observers may also have differing levels of expertise in plant
identification. If differences in species-richness estimates between individuals
are observed, correction factors can be applied post-hoc.
5.3.10 Other Important Data
Some data describing the wetland environment on a small scale can be easily
recorded during vegetation sampling.
Litter and peat: Wetlands can produce copious amounts of litter, which even-
tually may become peat. This litter can potentially suppress plant growth, and so
may be an important variable influencing the vegetation. Attributes such as litter
depth, percent cover, and type can be easily measured by sampling at one to
many locations within a plot. Peat depth and type may also be important in
structuring wetland plant populations and communities. Depth is easily
measured using
2 m marked plastic rod inserted into the ground. If peat is
deeper than the rod, then chances are the extra depth is not biologically signifi-
cant, and a dummy depth can be used for analysis purposes.
Bare ground: Bare ground within a wetland could signify disturbance, available
seed bed, or stressful conditions for plant growth. In any of these cases, it is
biologically interesting, and can be easily assessed using the percent-cover method.
Elevation or water depth: Water depth is critically important to wetland plant
growth and community structuring. It can be easily measured from the middle of a
plot (or subsampled) using a meter stick or tape measure. This type of local
measurement is a good supplement to staff gauge or piezometer information,
because it is at a smaller scale and may be more relevant to the plants. For more
intensive studies, survey equipment (laser level, tripod, and stadia rod) can be used
to assess the elevation of each plot. For smaller plots, a single measurement in the
plot center is adequate. For larger plots, multiple readings may need to be taken.
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