Transitions in forest fragmentation: implications for restoration opportunities at regional scales

Where the potential natural vegetation is continuous forest (e.g., eastern US), a region can be divided into smaller units (e.g., counties, watersheds ), and a graph of the proportion of forest in the largest patch versus the proportion in anthropogenic cover can be used as an index of forest fragmen tation. If forests are not fragmented beyond that converted to anthropogeni c cover, there would be only one patch in the unit and its proportional siz e would equal 1 minus the percentage of anthropogenic cover. For a set of 1 30 watersheds in the mid-Atlantic region, there was a transition in forest fragmentation between 15 and 20% anthropogenic cover. The potential for mit igating fragmentation by connecting two or more disjunct forest patches was low when percent anthropogenic cover was law, highest at moderate proporti ons of anthropogenic cover, and again low as the proportion of anthropogeni c cover increased toward 100%. This fragmentation index could be used to pr ioritize locations for restoration by targeting watersheds where there woul d be the greatest increase in the size of the largest forest patch.