Population Dynamics and Ecophysiology of Fraser fir (<i>Abies fraseri</i>) in the High Elevation Forests in the Southern Appalachian Mountains

Dominated by the endemic Fraser fir (Abies fraseri), the high-elevation forests of the Southern Appalachians are one of the most endangered ecosystems in the United States, and the future of these forests remains uncertain. Fraser fir is showing signs of decline in health and increased mortality throughout its range, possibly due to multiple environmental stresses.

Using twenty years of forest monitoring data, this dissertation documents change in forest structure and species composition in high-elevation red spruce-Fraser fir forests in southern Appalachia and generates predictions of future forest change. Additionally, it quantifies physiological measures of carbon fixation, storage and growth in adult Fraser fir in situ under multiple stresses, which has been unstudied previously, and explores environmental constraints associated with climate, soil chemistry and acidic deposition on physiological metrics.

We find no evidence of previously hypothesized shifts in forest composition to greater dominance of northern hardwood species. Using a stage-structured Baysian hierarchical model to predict Fraser fir populations through 2050, we predict robust recovery of populations on Clingmans Dome and Mount LeConte for at least the next several decades, as well as continued decline for populations on a number of mountains, notably Mount Sterling at the lowest end of Fraser fir’s elevation range. We find that maximum photosynthetic rates are low throughout the high elevation mountains of Great Smoky Mountains National Park, indicating trees are under considerable stress, but are highest in trees growing on the highest, steepest slopes. Trees from Clingmans Dome have significantly higher maximum photosynthetic rates and water use efficiency than trees on other mountains, which may indicate stress resistance in this population. Additionally both vi photosynthetic water use efficiency and leaf architecture are affected by maximum July temperature, suggesting future climate change will impact the foliar physiology of Fraser fir. Measurements of nonstructural carbohydrate pools are consistent with those found in mature trees of other species which suggests the capacity for resistance of future stress events, particularly at the highest elevations where photosynthetic rates are the highest.