Fragmentation of forest communities in the eastern United States
Forest fragmentation threatens the sustainability of forest communities in the eastern United States. Forest communities exhibiting either a low total area or low percentage of intact forest are subject to relatively higher risk of shifts in stand composition towards edge-adapted and invasive species. Such changes in stand composition could result in local extirpation of communities, homogenization of forest communities at broader spatial scales, and a consequential reduction of the biodiversity values of forestland. To evaluate current conditions, we combined forest inventory data with land cover data to compare 70 forest communities in terms of the amount and ownership of intact (i.e., not fragmented) forest, and the proximate causes (i.e., adjacent land cover) of fragmentation. Only 45% of total forestland area was intact in 4.41-ha neighborhoods, but that varied from 13% to 78% among forest communities. Among 10 community groups, the proximate causes of fragmentation reflected their typical geographic context, and the relative importance of fragmentation by development was higher in mostly-forested neighborhoods than in less-forested neighborhoods. Fragmentation was also higher on privately owned forestland than on public forestland. Because of the regional dominance of only a few forest communities and private land ownership, the total regional area of intact forest was driven more by the total area of those strata than by their fragmentation characteristics. The results provide insight for targeting land management strategies to maintain the diversity and regional distributions of intact forest communities.