The influence of historic anthropogenic disturbances on plant species diversity in forests of upstate New York is not well understood, but is a critical issue in assessing the current status and future direction of forest succession on state lands.  We assessed how understory plant species diversity and composition differ between natural forests, plantations, and “ruderal” forests (forests found on either former plantation or agricultural sites).  Plantation Forests (PF) were typically planted in the 1930s to restore abandoned agricultural lands. Many were left to mature for wildlife habitat and recreation value; others were harvested and allowed to succeed without replanting (hereafter Former Plantation forests or FPF).  Other abandoned agricultural lands were simply abandoned and allowed to succeed (hereafter Former Ag Land Forests FAF).  Native Northern Hardwood forests (NHF) showed no signs of soil profile disturbance, but may have been variously logged for lumber or firewood. We assessed 129 forest stands from a larger forest survey on New York State public forest lands using these four categories: PF - 50, FPF - 16, FAF - 13, NHF - 50 stands.   We controlled for abiotic (all stands are on relatively well-drained, low elevation sites in central-western New York’s northern hardwoods region) and biotic site differences (all stands in sapling/pole and mature stages because PF, FPF and FAF currently only occur in these stages).  We sampled overstory and understory vegetation in each stand with three 200 m² plots.  

Results/Conclusions

We found that FAF had the highest native and exotic plant species diversity and PF the lowest native plant species diversity.  Understory plant species composition differed between three of the forest categories (PF, FAF, NHF), but FPF overlapped in composition with PF and FAF.   Although FAF contain many native species, they are not necessarily transitioning to natural stands, as both the overstory and the regeneration layers of these ruderal stands either lack or have low proportions of key northern hardwood tree species (i.e., Acer saccharum, Betula allegheniensis, Fagus grandifolia, Tsuga canadensis).  FPF appear to be transitioning from PF to FAF, rather than to NHFs.  Despite the extensive regrowth of forest cover in central-western New York over the past 70 years, the composition of modified or ruderal forests still differs significantly from the native northern hardwood forests typical of the region.