Effects of agricultural soil loss on forest succession rates and tree diversity in east Tennessee

All land on what is today the Oak Ridge Reservation. Tennessee, was abandon ed in 1942 when the United States government acquired the land for atomic w eapons development. Most of the land now serves as a buffer around the gove rnment facilities and has not been managed, providing an opportunity to stu dy forest succession on simultaneously abandoned fields. We sampled forest vegetation and soils on former pastures that had sustained varying levels o f pre-abandonment soil loss. The most eroded sites are still covered with f orests of an early-successional composition, with shortleaf pine (Pinus ech inata) and Virginia pine (P. virginiana) dominating. Hardwoods, particularl y oaks (Quercus) and hickories (Carya), dominate the lease degraded former pastures. Canopy tree species diversity is highest at the least degraded si tes, which also have the highest levels of soil nitrogen. These results sug gest that soil degradation reduces the rate of secondary succession and the reby slows the increase in species diversity typical of early forest succes sion, while increasing the spatial complexity of the landscape.