USING AN INDEX OF HABITAT PATCH PROXIMITY FOR LANDSCAPE DESIGN

A proximity index (PX) inspired by island biogeography theory is descr ibed which quantifies the spatial context of a habitat patch in relati on to its neighbors. The index distinguishes sparse distributions of s mall habitat patches from clusters of large patches. An evaluation of the relationship between PX and variation in the spatial characteristi cs of clusters of patches showed that reduction in the isolation of pa tches within a cluster produced exponential increases in PX, and that increase in the size of those patches produced a more modest linear in crease in PX. Simulations using neutral model landscapes were used to determine the effect of the scale of analysis on PX. Increased size of the neighborhood considered around a habitat patch (proximity buffer) produced linear increases in PX, the slope being dependent on the pro portion of the habitat of interest on the landscape. The proximity ind ex was used to evaluate three alternative conservation reserve designs in an agricultural landscape, and comparisons were made among designs consisting of the same area of forest habitat added to the landscape. The 'single, large' reserve design produced the greatest increase in mean PX values among forest patches on the landscape when the total ar ea of forest added was greater-than-or-equal-to 842 ha, and the 'sever al, small' reserve design produced the greatest increase when the tota l area of forest added was less-than-or-equal-to 716 ha. The 'string-o f-pearls' reserve design produced mean PX values approximately equal t o those of the 'single, large' configuration when the total area of fo rest added was less-than-or-equal-to 716 ha and the proximity buffer w as greater-than-or-equal-to 2.1 km, since the 'string-of-pearls' confi guration produced a higher total number of neighbors around the added reserves, which helped offset the smaller size of each reserve. Large reserves have more area, but their influence is limited to fewer neigh bors. There appears to be a size threshold where the increased area of single, large reserves produced higher PX values than other configura tions that influence more neighbors. Visualization of the spatial dist ribution of PX values across the landscape can reveal how organisms wi th specific movement scales might perceive the effective fragmentation of the landscape (spatial variability of PX), further aiding conserva tion reserve planning and design.