Geoscience Reference
In-Depth Information
16.4.3
Landscape Simulations
16.4.3.1
Ecotone Abruptness
The results of the analysis of metric sensitivity to the abruptness of ecotones suggested that
existing landscape metrics were not as useful for quantifying ecotone abruptness as were the new
metrics specifically designed for that purpose (Bowersox and Brown, 2001). Some metrics (e.g.,
total edge, maximum subgraph length) were not sensitive to abruptness. Those sensitive to abruptness
were also sensitive to landscape patchiness, which confounded their interpretation (i.e., numbers of
boundary elements and subgraphs, area-weight mean shape index). The new metrics, dispersion of
boundary elements and cumulative boundary elements, were most consistently related to abruptness
while not exhibiting the confounding effects of sensitivity to patchiness. There was not a clear
indication that patch- or boundary-based metrics were more or less sensitive to abruptness.
16.4.3.2
Forest Fragmentation
Using simulated landscapes, each of several patch-based metrics exhibited a significant degree
of variation when calculated at different levels of percent forested (Figure 16.3, top panel). Edge
density was clearly highest when the landscape was 50% forest and lowest when the landscape
was either 100% or 0% forest. The largest patch index and the total core area index both increased
with increasing percentage of forest. The number of patches decreased with increasing forest
percentage, after an initial increase.
The number of patches exhibited the highest degree of variation across different simulation
runs (Figure 16.3, top panel). The coefficient of variation across simulation runs varied at different
levels of percentage forest, depending on the average value of the metric and its variance (Figure
300
250
200
Largest Patch Index
# Patches
Edge Density
Total Core Area Index
150
100
50
0
0
20
40
60
80
100
Percent Forest
0.45
0.4
0.35
Largest Patch Index
# Patches
Edge Density
Total Core Area Index
0.3
0.25
0.2
0.15
0.1
0.05
0
0
20
40
60
80
100
Percent Forest
Figure 16.3
Top panel: The relationships between mean landscape pattern metric values across 10 simulations
and the proportion of the landscape covered by forest. The error bars show the two times the
standard deviation across the 10 runs. Bottom panel: The coefficient of variation of the metric
values across simulations, indicating their relative errors.
