Effects of roads on landscape structure within nested ecological units of the Northern Great Lakes Region, USA

Road development is a primary mechanism of fragmentation in the northern Great Lakes Region, removing original land cover, creating edge habitat, altering landscape structure and function, and increasing access for humans. We examined road density, landscape structure, and edge habitat created by roads for eight land cover types at two ecological extents within a 78,752 km(2) landscape. Road density ranged from 0.16 to 2.07 km/km(2) within land type associations. Between 5 and 60% of a land cover type was affected by roads, depending on the assumed depth-of-edge influence (DEI). Roads increased number of patches and patch density, and decreased mean patch size and largest patch index. Changes in patch size coefficient of variation and measures of patch shape complexity depended on ecological level (i.e. scale) and land cover class. Limited additional change in landscape metrics occurred as road DEI was increased from 20 to 300 m. Land cover type occurred in buffers at the same percentages as in the landscape as a whole. At finer extents, areas with greatest road densities did not always parallel those with greatest changes in landscape structure. Interactions of scale and variation in the distribution of roads across the region emphasize the importance of examining landscape metrics and road impacts within specific cover types and at appropriate, or multiple, scales. Although this region is densely forested, the fragmentation effects of roads are pervasive, significantly altering landscape structure within multiple forest cover classes and at differing ecological extents. (C) 2001 Elsevier Science Ltd. All rights reserved.