Print PageChanges in tree species distributions are a potential impact of climate change on forest ecosystems. In the past, the examination of tree species shifts in forests of the eastern United States has been limited to simulation activities due to a lack of consistent, long-term forest inventory datasets across large geographic scales. The adoption of a spatially balanced and annualized forest inventory in 1999 by the USDA Forest Service affords the opportunity to investigate large-scale in-situ tree migration. We explore the results of multiple studies that investigate analytical techniques for using forest inventory (FIA) data to detect shifts in the geographic ranges of tree species across the eastern United States (U.S.). Due to the statistical inability to compare current tree ranges derived from FIA data to historic delineations of tree ranges, a number of novel techniques have been explored using both forestland and urban tree inventory information coupled with concepts of tree demography.
Results/Conclusions
Using tree demography as an indicator of tree range shifts, the mean latitude of tree seedlings was significantly farther north (>20 km) of their respective adult trees (i.e., tree biomass) for study tree species found at northern U.S. latitudes. In contrast, southern tree species had no apparent mean latitudinal shift with general species demonstrating a possible shift in a southern direction. Density of seedlings relative to tree biomass of northern tree species was nearly 10 times higher in northern edges of their respective ranges as compared to southern edge of their respective ranges. Results suggest that the process of tree range shifts in the eastern United States is currently underway with rates approaching 100 km/century for many species. However, a sensitivity analysis indicated that this study’s conclusions were highly dependent on the study species selection. It is suggested that examining species most likely to migrate provides objective species lists for migration detection. In contrast, the inclusion of all tree species commonly observed in large-scale forest inventories can obfuscate migration detection with tree species that have little ecological reason to immediately migrate in a changing climate. The ability of urban tree seed sources to serve as a facilitator of forest tree range migration was also explored indicating that urban areas may serve divergent, dual roles as both a native tree seed source and refuge for a limited number of forestland tree species, but also a facilitator of non-native tree invasion.
