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FUNCTIONAL HETEROGENEITYANALYSIS :
A TECHNIQUE THAT USES BOTH PATTERNAND SCALE
MEASURED LANDSCAFE FUNCTIONAL LANDSCAPES
Moving-Window Application of
the Weighted Connectivity Index
1 2
* grayshadesindicatemapped • sizeof movingwindowcorrespondsto scaleof energy,
landscapezones material,ororganismflows
, grayshadesindicateindexvalues
.... ;IFT]
1, closelyresemblesmeasured :3 ° vaguelyresemblesmeasured
landscape landscape
°onlyboundariesare ° indexvaluesspatiallyvaried
heterogeneous ° landscapeis functionally
heterogeneous
Figure 4.--Functional heterogeneity analysis using pattern recognition algorithms and moving-window calculations.
Relating Functional Heterogeneity to Epidemiology of D. frontalis
Although D. frontalis is among the most thoroughly studied pest species, there is no mechanistic explanation for how
the natural history of the insect operates at the landscape scale to produce observed patterns of epidemiology (Dunning et al.
1992). We suggest that bark beetle epidemiology in a pine forest landscape involves a network of [i] lightning-struck hosts
(Lovelady 1994), which serve as sinks during dispersal (Pullian 1988, Pullian and Danielson 1991); [ii] previous existing
infestations, which serve both as sources and sinks; and [iii] high hazard stands, which also serve as sinks and are needed for
development of infestations. With only modest requirements for dispersal distance (1 kin), the bark beetles can reduce high
measured heterogeneity in pine forest landscapes into high functional homogeneity, i.e., the insects can link dispersed food
and habitat resources. Specific attributes of landscape structure will influence how this scenario is played out in different
forest environ ments.
In the following example, we examine how D. frontalis interacts within a meso-scale (100 to 1,000,000 ha) forest
landscape. The GIS-based study (McFadden 1994) was conducted on the Sam Houston National Forest in southeast Texas.
This landscape is vegetated primarily with loblolly, Pinus taeda L., and shortleaf, P echinata Mill, pines and mixed hardwood
species. Populations of D. frontalis in the forest have cycled from enzootic to epizootic levels for more than two
decades.
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