Predicting Climate Change Extirpation Risk for Central and Southern Appalachian Forest Tree Species

—Climate change will likely pose a severe threat to the viability of certain forest tree species, which will be forced either to adapt to new conditions or to shift to more favorable environments if they are to survive. Several forest tree species of the central and southern Appalachians may be at particular risk, since they occur in limited high-elevation ranges and/or are currently threatened by nonnative insects and diseases. We are beginning an assessment of potential climate change impacts on more than 100 North American forest tree species, using the innovative Multivariate Spatio-Temporal Clustering (MSTC) technique. Combining aspects of traditional geographical information systems and statistical clustering techniques, MSTC statistically predicts environmental niche envelopes to forecast species’ geographic ranges under altered environmental conditions such as those expected under climate change. We outline the objectives of this project, present some preliminary results for central and southern Appalachian tree species, and discuss the need for assistance from fellow scientists in the development of this work. 1 Research Assistant Professors (KMP and FHK), Department of Forestry and Environmental Resources, North Carolina State University, 30410 Cornwallis Road, Research Triangle Park, NC 27709; Landscape Ecologist (WWH), Eastern Forest Environmental Threat Assessment Center, USDA Forest Service, Southern Research Station, 200 Weaver Blvd., Asheville, NC 28804. KMP is corresponding author: to contact, call (919) 5494071 or email at [email protected]. adaptation, 2) migration (range shift), or 3) extirpation (Davis et al. 2005). Although some evidence exists that trees have the capacity to evolve rapidly to new environmental conditions (Petit et al. 2004), adaptation via natural selection may be unlikely in many cases, given the long generation time for forest tree species (St. Clair and Howe 2007). Rehfeldt et al. (1999), for example, predict that tree adaptation to climate change would take 1 to 13 generations, or 100 to 1,000 years. Tree species successfully migrated long distances during the climate changes of the Pleistocene, but may not be able to match climate shifts anticipated in the near future because they are expected to occur much more rapidly (Davis and Shaw 2001). Even when tree species possess propagule dispersal mechanisms that allow them to shift their ranges, their effective migration may be impeded by forest fragmentation (Opdam and Wascher 2004), they may experience inbreeding-reduced genetic diversity as a result of founder effects (Petit et al. 2004), and their genetically important “trailing edge” populations may be extirpated (Hampe and Petit 2005). It is worth noting that some of the most genetically distinct Appalachian populations of at least one forest tree species, eastern hemlock (Tsuga canadensis [L.] Carr.), are located near the very southern end of the range (Potter et al. 2008a). Forest tree species or populations that are not able to shift their distribution or adapt in response to changing climatic conditions may instead face extinction or local extirpation. This possibility may be a concern particularly for species that have narrow habitat requirements, are located exclusively at high elevations, and/or are not able to disperse their propagules effectively across long distances. Even if not extirpated outright, populations of these and other species could experience significant inbreeding, genetic drift, and decreased genetic variation as a result of reduced population size. Such populations may then become more susceptible to mortality caused both by nonnative pests and pathogens and by the environmental pressures associated with climate change. This susceptibility could generate a cycle of mortality, loss of genetic variation, and inability to adapt to change that could ultimately result in population extirpation (Fig. 1). Within the central and southern Appalachians, three forest tree taxa likely to be at greatest risk of extinction as a result of climate change are Fraser fir (Abies fraseri [Pursh] Poir.), intermediate balsam fir (Abies balsamea [L.] Mill. var. phanerolepis Fern.), and Carolina hemlock (Tsuga caroliniana Engelm.). All three are limited to small, high-elevation populations, and are under siege from exotic pests: the balsam woolly adelgid (Adelges piceae Ratz.) in the case of Fraser fir (Dull et al. 1988) and intermediate balsam fir (Bross-Fregonara 2002), and hemlock woolly adelgid (Adelges tsugae Annand) in the case of Carolina hemlock (Jetton et al. 2008). Other species, such as Table Mountain pine (Pinus pungens Lamb.), red spruce (Picea rubens Sarg.), and striped maple (Acer pensylvanicum L.) are less likely to experience range-wide extinction, but could have their southern and central Appalachian populations eliminated as a result of changing climate conditions. These populations may contain unique genotypes resulting from long-term biogeographical processes and from selection pressures that may be different from those experienced by these species in their more northerly populations. We are in the early stages of a large-scale assessment of the risk posed by climate change to the genetic integrity of many North American species. Central to this project is the application of the innovative Multivariate Spatio-Temporal Clustering (MSTC) technique (Hargrove and Hoffman 2005). We are using MSTC to predict the future location and quality of habitat for tree species and, along with consideration of species’ biological attributes, will assess whether range-shifting tree species might be able to track appropriate environmental conditions over time and avoid the loss of extensive genetic variation. We here present preliminary results for four southern and central Appalachian forest tree species.