The area of each watershed with the potential for soil losses greater than 1 ton per acre per year was then found by summing the number of pixels in each watershed that exceeded this threshold value. The indicator is the proportion of the watershed above that threshold value. The cookie-cutter procedure to extract the land cover information was applied to each watershed separately. The number of pixels with forest land cover was then counted in each watershed, and the total was divided by the total number of pixels for a given watershed to yield the per-watershed index value. The fragmentation statistic measures the probability that a randomly selected forested spot in a watershed is not adjacent to another forested spot.
Higher values indicate higher fragmentation.
The statistic was calculated separately for the forest cover within each watershed in the mid-Atlantic region, rather than using a sliding window technique. Forest edge habitat differences among watersheds were assessed by the sliding window technique. The fragmentation indicator described above was used, but calculated in a small window that was placed within a watershed. If the calculated indicator value exceeded one-half the maximum value for that amount of forest, then the center of the window was marked as suitable edge habitat. After moving the calculation window throughout the watershed, the proportion of the watershed that was labeled suitable was calculated and used as the indicator value.