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setting, matrix susceptibility can be viewed as the tendency for Douglas
fir trees to resist bark beetle infestation. In a heterogeneous, vital old
growth stand, matrix susceptibility would be expected to be relatively low
disturbance spread where would eventually die out despite initial patch
size and potential rate of spread. Thus, the high matrix-patch contrast
would act to insulate and isolate patches and retard disturbance spread.
On the other hand , a landscape characterized by high susceptibility might
correspond to aggregates of stressed trees (e.g., densely grouped young
conifers). The weakened forest matrix would be less effective at resisting
an outbreak. According to the model, propagation would occur locally at
a faster rate. Levels of matrix heterogeneity, landscape connectivity, and
dispersal capabilities of the insect would interact to determine the rate
of spread .
In a second scenario, we consider conifer regeneration in a patchy
landscape. In this case, the old growth and mature stands constitute the
patches; the matrix is composed of young conifer and deciduous stands.
The potential for conifer seedling establishment would be relatively high
if the surrounding matrix was open and resource availability was not
blocked by the presence of dense alder stands. In this case, matrix
susceptibility would be considered high. Conversely, the presence of thick
alder stands in the matrix would render seedling establishment more
difficult and retard conifer regeneration. A similar scenario would be
applicable for the dispersal patterns of faunal communities in the patchmatrix landscape.
Conclusions
Terrestrial ecology is now at the juncture where field and experimental
analyses may be combined with the concepts of patch dynamics and
hierarchy theory to develop a coherent spatially explicit, across-scale
understanding of forest dynamics. Understanding what controls the rate
and direction of local interactions as a function across spatial scales will
be critical to developing appropriate management and conservation plans.
We have engaged in a simple experiment to evaluate the effects of two
elements of spatial pattern (i.e. , patch-matrix contrast and patch size) on
the rate and direction of landscape change. Two processes characteristic
of Pacific Northwest forests, disturbance and regeneration, were discussed
within the model context.
The model results suggest that anthopogenically introduced heterogeneity at a local level can dominate overall landscape change. Deviations
in local patch-matrix interactions and pattern can effect significantly
different rates of landscape change and the outcome of landscape composition. A differential in rates of change has several implications. If the
rate of change effected by local patch-matrix interactions is slow relative
G.A. Bradshaw et al.
setting, matrix susceptibility can be viewed as the tendency for Douglas
fir trees to resist bark beetle infestation. In a heterogeneous, vital old
growth stand, matrix susceptibility would be expected to be relatively low
disturbance spread where would eventually die out despite initial patch
size and potential rate of spread. Thus, the high matrix-patch contrast
would act to insulate and isolate patches and retard disturbance spread.
On the other hand , a landscape characterized by high susceptibility might
correspond to aggregates of stressed trees (e.g., densely grouped young
conifers). The weakened forest matrix would be less effective at resisting
an outbreak. According to the model, propagation would occur locally at
a faster rate. Levels of matrix heterogeneity, landscape connectivity, and
dispersal capabilities of the insect would interact to determine the rate
of spread .
In a second scenario, we consider conifer regeneration in a patchy
landscape. In this case, the old growth and mature stands constitute the
patches; the matrix is composed of young conifer and deciduous stands.
The potential for conifer seedling establishment would be relatively high
if the surrounding matrix was open and resource availability was not
blocked by the presence of dense alder stands. In this case, matrix
susceptibility would be considered high. Conversely, the presence of thick
alder stands in the matrix would render seedling establishment more
difficult and retard conifer regeneration. A similar scenario would be
applicable for the dispersal patterns of faunal communities in the patchmatrix landscape.
Conclusions
Terrestrial ecology is now at the juncture where field and experimental
analyses may be combined with the concepts of patch dynamics and
hierarchy theory to develop a coherent spatially explicit, across-scale
understanding of forest dynamics. Understanding what controls the rate
and direction of local interactions as a function across spatial scales will
be critical to developing appropriate management and conservation plans.
We have engaged in a simple experiment to evaluate the effects of two
elements of spatial pattern (i.e. , patch-matrix contrast and patch size) on
the rate and direction of landscape change. Two processes characteristic
of Pacific Northwest forests, disturbance and regeneration, were discussed
within the model context.
The model results suggest that anthopogenically introduced heterogeneity at a local level can dominate overall landscape change. Deviations
in local patch-matrix interactions and pattern can effect significantly
different rates of landscape change and the outcome of landscape composition. A differential in rates of change has several implications. If the
rate of change effected by local patch-matrix interactions is slow relative