Upslope shifts in vegetation establishment have been documented through empirical studies, consistent with hypotheses relating warming to range shifts.  However, because observations have been located within specific topographic landscapes, these studies may not be representative of the range of topographic complexity in a region and shifts are difficult to forecast across broad spatial extents. The Appalachian Mountains host a high diversity of plants, partly due to topographic complexity, and the mountain range provides an important setting in which to explore  topographic indices across a north-south ecotonal gradient.  Here, we develop topographic indices for several Appalachian landscapes, to quantify how slope and elevation govern the area of suitable vegetation habitat.  We hypothesize that steeper slopes, with higher temperature lapse rates, provide greater opportunities for upslope shifts as a response to climate change and that steeper topographies also preserve habitat area as elevation increases as compared to gentle slopes where habitat area decreases rapidly with elevation. Digital elevation models (30 m resolution) were used as a proxy for temperature lapse rates and indices were developed that describe cumulative changes in 3-dimensional area with elevation.

Results/Conclusions

A statistical analysis of 10,000 ha DEM clips in the southern Appalachians (Georgia and North Carolina), central Appalachians (Pennsylvania), and northern Appalachians (New Hampshire) shows considerable similarity between the northern and southern Appalachians while patterns in the central Appalachians differ. The southern and northern Appalachians have greater elevational ranges on average (880 m and 930 m respectively) than the central Appalachians (360 m) and therefore have a greater potential diversity of climate niches. The landscapes in the southern and northern Appalachians, which have steeper slopes than the central region, also lose less surface area with increasing elevation than the central region. On average, 3-dimensional surface area decreases by 0.17% for each meter of elevation gain in the southern Appalachians and by 0.18% per meter in the northern Appalachians. By contrast, in the central Appalachians land surface decreases by 0.35% per meter. These results imply a potentially higher rate of change in suitable habitat in the central Appalachians than in the southern and northern Appalachians with upslope migration in response to predicted warming. This research will help prioritize conservation activities including assisted migrations of threatened species and may help explain past species migrations within this complex topography.