Regional Flow Patterns

The regional flow patterns dataset mapped here was designed to identify potential larger-scale directional movements and pinpoint the areas where they are likely to become concentrated, diffused, or rerouted, due to the structure of the landscape. We used the software tool Circuitscape (McRae and Shah 2009, http://www.circuitscape.org /) based on electric circuit theory, to model these larger flow patterns for the region. Like the local connectedness analysis, the underlying data for this analysis was land-cover and road data converted to a resistance grid by assigning weights to the cell types based on their similarity to cells of natural cover. However, instead of quantifying local neighborhoods, the Circuitscape program calculates a surface of effective resistance to current moving across the whole landscape. The output of the program, an effective resistance surface, shows the behavior of directional flows. Analogous to electric current or flowing water, the physical landscape structure creates areas of high and low concentrations similar to the diffuse flow, braided channels, and concentrated channels one associates with a river system. Three basic patterns can be seen in the output, as the current flow will: 1) avoid areas of low permeability, 2) diffuse in highly intact/highly permeable areas, or 3) concentrate in key linkages where flow accumulates or is channeled through a pinch point. Concentration areas are recognized by their high current density, and the program’s ability to highlight concentration areas and pinch-points made it particularly useful for identifying the linkage areas that may be important to maintaining a base level of permeability across the whole region.