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G.A. Bradshaw et al.
spatial pattern are varied-mean patch size and patch-matrix contrast, as
defined below. The initial landscapes have the same ratio of patch-tomatrix areas. Patterns resulting from patch-matrix contrast are examined
by using a nearest-neighbor algorithm moved across the landscape of a
given patch-size configuration. Depending on the cell type encountered
(either patch or matrix) and the interaction algorithm applied, local
change in landscape composition will occur. Patches are first-order
approximations of harvested stands in a forest matrix; conversely, patches
may be intact ' old growth stands within a matrix of young or harvested
land (Figure 14.14).
Variability in patch size is achieved by specifying a mean patch radius
and generating a normally distributed patch landscape. The patch-matrix
contrast is varied in two ways: (1) radius of influence and (2) matrix
susceptibility. A small radius of influence implies that only cells located in
the immediate neighborhood of the patch will change; a large radius of
influence implies that a larger zone of influence is exterted by the patch
on the matrix. A difference in radii of influence is intended to correspond
to rapid local change. Matrix susceptibility is defined as the tendency for
the matrix to become patch. High susceptibility,corresponds to an asymmetry in the direction of change between patch and matrix (i.e., low
resistance of the matrix to resist patch-induced change) (Figure 14.15).
Results
The greatest difference exerted by these three parameters is associated
with matrix susceptibility values. Under conditions of low susceptibility,
the landscape changes over to matrix (Figure 14.16). Conversely, under
conditions of high susceptibility, all four variants asymptotically approach
a landscape composed of patch composition (Figure 14.17). Within each
category, the effects of patch size and radius of influence have a lesser
impact, but trends are visible. In the low susceptibility case (Figure
14.6b), the presence of a small radius of influence for patches of both
sizes causes the landscape to converge to the forest matrix more rapidly
in comparison to conditions where the radius of influence is high. As
indicated by the case of small patches, total patch area increases. However, this trend reverses and the landscape eventually converges to forest
matrix. In contrast (Figure 14.6a), patch size and radii of influence under
conditions of high susceptibility appear to have a less noticeable effect
on landscape change behavior; the rate and direction of change are
dominated by the condition of high-matrix susceptibility and convergance
is much more rapid. The experiment illustrates that local interactions and
spatial relationships can effect vastly different landscape development and
composition despite differences in local patterns. This experiment also
illustrates the concept of a threshold; namely, the direction of landscape
G.A. Bradshaw et al.
spatial pattern are varied-mean patch size and patch-matrix contrast, as
defined below. The initial landscapes have the same ratio of patch-tomatrix areas. Patterns resulting from patch-matrix contrast are examined
by using a nearest-neighbor algorithm moved across the landscape of a
given patch-size configuration. Depending on the cell type encountered
(either patch or matrix) and the interaction algorithm applied, local
change in landscape composition will occur. Patches are first-order
approximations of harvested stands in a forest matrix; conversely, patches
may be intact ' old growth stands within a matrix of young or harvested
land (Figure 14.14).
Variability in patch size is achieved by specifying a mean patch radius
and generating a normally distributed patch landscape. The patch-matrix
contrast is varied in two ways: (1) radius of influence and (2) matrix
susceptibility. A small radius of influence implies that only cells located in
the immediate neighborhood of the patch will change; a large radius of
influence implies that a larger zone of influence is exterted by the patch
on the matrix. A difference in radii of influence is intended to correspond
to rapid local change. Matrix susceptibility is defined as the tendency for
the matrix to become patch. High susceptibility,corresponds to an asymmetry in the direction of change between patch and matrix (i.e., low
resistance of the matrix to resist patch-induced change) (Figure 14.15).
Results
The greatest difference exerted by these three parameters is associated
with matrix susceptibility values. Under conditions of low susceptibility,
the landscape changes over to matrix (Figure 14.16). Conversely, under
conditions of high susceptibility, all four variants asymptotically approach
a landscape composed of patch composition (Figure 14.17). Within each
category, the effects of patch size and radius of influence have a lesser
impact, but trends are visible. In the low susceptibility case (Figure
14.6b), the presence of a small radius of influence for patches of both
sizes causes the landscape to converge to the forest matrix more rapidly
in comparison to conditions where the radius of influence is high. As
indicated by the case of small patches, total patch area increases. However, this trend reverses and the landscape eventually converges to forest
matrix. In contrast (Figure 14.6a), patch size and radii of influence under
conditions of high susceptibility appear to have a less noticeable effect
on landscape change behavior; the rate and direction of change are
dominated by the condition of high-matrix susceptibility and convergance
is much more rapid. The experiment illustrates that local interactions and
spatial relationships can effect vastly different landscape development and
composition despite differences in local patterns. This experiment also
illustrates the concept of a threshold; namely, the direction of landscape