Predicting the potential future distribution of four tree species in ohio using current habitat availability and climatic forcing

We investigated the effect of habitat loss on the ability of trees to shift in distribution across a landscape dominated by agriculture. The potential distribution shifts of four tree species (Diospyros virginiana, Oxydendron arboreum, Pinus virginiana, Quercus falcata var. falcata) whose northern d istribution limits fall in the southern third of Ohio were used to assess p ossible distribution shift scenarios as a result of global warming. Our pre dictions derive from the results of simulations using (a) forest inventory based estimates of current distribution and abundance of target species; (b ) a satellite-based estimate of forest habitat availability; and (c) a tree migration model (SHIFT). The current distribution and abundance of trees w as estimated using USDA Forest Service's Forest Inventory Analysis data and distribution maps from the late 1960s; pre-European settlement forest-nonf orest maps were used to represent the fully forested condition for calibrat ion and comparison. Habitat-availability estimates in Ohio were estimated u sing classified Landsat Thematic Mapper (TM) data from 1994. Tree abundance , forest availability and migration were modeled using a 1-km(2) pixel size . Forest availability was estimated as the proportion of forested TM pixels within each cell. The probability of a migrating species colonizing an uno ccupied cell is modeled as a function of forest availability and distance t o occupied cells. The results of the migration models suggest that the spec ies studied are capable of colonizing virtually any forested location withi n Ohio over the next 100 years if climatic controls over the current distri bution that may currently inhibit northward movement are relaxed. The conti guous distribution of these species, however, is not likely to shift more t han 10 km during the next century regardless of the magnitude of the climat e change. Examining the sensitivity of our simulations by varying critical model attributes, we found that whereas the variables controlling the amoun t of long-distance dispersal have strong effects on migration rates in the fully forested 1800 situation, they have significantly lesser effects on pr ojections of future migration into highly fragmented forests. The low fores t availability that characterizes much of the current Ohio landscape, along with the low likelihood of long distance dispersal, result in potential di stribution shifts that are concentrated within the principally forested cor ridors in southeastern Ohio. We propose that in contrast to the past, futur e tree migrations are likely to be spatially and temporally correlated as a result of large climatic forcing and channelization through limited region s of available habitat. With respect to the management of biodiversity, thi s result suggests that it may be very difficult to discern plant migrations of native forest species owing to exceedingly slow rates of movement.