Environmental Engineering Reference
In-Depth Information
Fig. 5.3 Nested plots.
(a) Vegetation of different
strata can be sampled within
differently-sized nested
plots. (b) Different types of
data can be sampled within
nested plots, corresponding
to the organism studied
Table 5.1 Example line intercept data sheet for a line 5.0 m long
Species
Intercepts (m)
Total length (m) % intercept
Calamagrostis canadensis
0.5-0.8, 1.2-1.7, 2.9-3.5, 4.8-5.0
1.6
32.0
Chamaedaphne calyculata
0.7-1.3, 3.9-4.1
0.6
12.0
Myrica gale
0.0-0.6, 1.6-3.0, 3.4-3.8
2.4
48.0
Typha latifolia
0.0-0.2
0.2
4.0
Spiraea alba
4.0-4.9
0.9
18.0
different strata. In this case, understory vegetation is typically sampled in a small
rigid frame at the center of the plot, and then successively larger circular plots are
used to survey shrubs and then trees (Fig.
5.3a
). Nested plots may also be effective
in collecting different types of data at different scales. For example, individual plant
count data may be collected in a subsample of small quadrats within a larger plot
that is surveyed for trees or non-vegetation-related ecological attributes (Fig.
5.3b
).
One of the most complex uses of nested plots is to determine the rate of species
accumulation over larger and larger areas (Barbour et al.
1998
). In this use, the
investigator first surveys a series of small quadrats, recording species. Then, within
subsequently larger plots, repeats the procedure, adding any new species. The
results can be used to determine the most effective plot size for characterizing
community or population attributes (the plot size where there is little subsequent
change in your estimates). Finally, nested plots can be used to assess the spatial
pattern of a plant population or community (Dale
1998
; Greig-Smith
1983
).
The line-intercept technique is essentially a variation upon the plot technique in
which the plot is one-dimensional (very long but with no width). A line is created
with a meter tape, and vegetation is measured wherever it intersects the vertical
plane created by the tape (both above and below). A data sheet for line-intercept
data includes the species that intersect the line, and the distances at which they
intersected it (Table
5.1
). Line intercept data can be quicker to collect than quadrat
data when there are few species and large areas to be covered. A challenge is
comparing the intercept of a graminoid (grass-like) species to those of species that
have more two-dimensional coverage (like shrubs). Additional challenges include
deciding when to start and end the continuous intervals of intercept with plants that
are not themselves continuous over the entire interval. The belt-transect method is a
