Anthropogenic Fragmentation in the western United States

We evaluated the fragmentation of the western United States by anthropogenic features. The addition of roads, railroads, and power lines to wildlands, and the conversion of wildlands to agricultural land and/or urban areas, induces fragmentation. We used the following spatial data sets to model anthropogenic fragmentation: agricultural land, populated areas, power lines, railroads, and roads. Because we were interested in the spatial arrangements of wildland patches and how anthropogenic fragmentation affects wildlife dispersal, we buffered some of these spatial data sets according to their area of influence. For example, the area of influence of interstate highways extends beyond the traffic lanes (Rowland et al. 2000, Brotons and Herrando 2001, Rheindt 2003), we therefore buffered each interstate highway by 1km. Similarly, we reasoned that the area of influence of federal and state highways, railroads and power lines extends well beyond the actual line feature; each anthropogenic feature was therefore buffered by 0.5km. All of these buffered spatial data sets were combined in ARC/INFO using the MERGE command, reclassified to 1 = anthropogenic feature and 0 = wildland, and resampled to 180m resolution. Using this input layer, we performed a moving window analysis to calculate the percentage of cells occupied by anthropogenic features using a 54.5km quadrate as the analysis window (303 * 303 cells, area = 2975 km2). This analysis window size approximates the upper home range size of a sage-grouse (Connelly et al. 2000).