Land Use and Forest Dynamics at Harvard Forest 1937-2013

Modern vegetation patterns have developed as a result of species response to environmental gradients, disturbance history, and biotic interactions. However, the relative importance of environmental versus historical factors in determining modern species distributions may differ from site to site and may change with increasing time since disturbance. In addition, life-forms may differ in their response to environmental versus historical disturbance gradients. In the current study, we relate vegetation patterns across the Prospect Hill Tract of Harvard Forest to variability in edaphic factors and disturbance histories. Modern species distribution patterns are related to both edaphic and disturbance gradients. Although species respond individualistically to edaphic and disturbance gradients, land-use history, soil drainage, and C:N ratio are good predictors of the distribution of many species. In contrast, 1938 hurricane damage is less important. Vascular species richness is related to historical land-use, with fewer species in historical woodlots than on former agricultural sites. This is contrary to what has been reported from several other studies, and may reflect the dominance of historical woodlots in the study area by hemlock, a species that creates environmental (i.e. light and soil) conditions that are unsuitable for many species. Historical land-use does not appear to influence bryophyte species richness, although the distributions of several species do follow patterns of land-use. Species richness also varies according to soil drainage, with higher bryophyte, herb, and shrub richness and lower overstory and understory tree richness on wetter sites.