FRAGMENTATION OF A FORESTED ROCKY-MOUNTAIN LANDSCAPE, 1950-1993

Patterns of change in landscape structure in a portion of the Hayden D istrict of the Medicine Bow National Forest in southeastern Wyoming ha ve been driven primarily by clearcut logging from 1950 to 1993; no maj or fires or wind storms have occurred in the study area during this ti me. Two distinct data sets, created from information in the Resource I nformation System database of the USDA Forest Service, were used as th e basis for a quantitative analysis of landscape change. Forest fragme ntation was quantified using a geographical information system (GRASS 4.1) to calculate indices of landscape structure. Increases in number of patches (1012 to 1331), total perimeter (3980 to 4400 km), Shannon diversity (2.36 to 2.63), contrast (2.49 to 2.68), and sum of edges (1 19.1 to 121.2 km) were accompanied by decreases in mean patch size (29 .5 to 22.5 ha), mean patch shape (2.16 to 2.05), mean patch perimeter (3.91 to 3.3 km), dominance (1.04 to 0.81), contagion (4.30 to 4.07), and angular second moment (0.14 to 0.10). The observed trends in lands cape pattern indicate increasing forest fragmentation since 1950. The study area landscape in 1993 is more fragmented than the landscape of the Oregon Cascades, now the subject of national attention and restora tion action. As in other fragmented landscapes, the results suggest th at previous management practices have lacked monitoring and analysis o f landscape-scale impacts, indicating that increased attention to the landscape-scale is needed in future management actions.