Disturbance and long-term vegetation change in the high-elevation deciduous forests of Great Smoky Mountains National Park

Vandermast, David

This dissertation examines temporal changes in forest attributes such as tree density, basal area and woody understory composition using long-term data sets from deciduous forests at high-elevations in Great Smoky Mountains National Park. The chapters contained herein will test, with empirical data, assumptions of the stability of late-successional temperate deciduous forests in the study area. The high-elevation deciduous forests of Great Smoky Mountains National Park (GRSM) are one of the largest relatively undisturbed forest landscapes in the eastern United States. They are a reference point for late-successional temporal forest dynamics and in this study I use data from them to ask: (1) whether tree densities, basal areas, and biomass in high-elevation forests remain constant over time, (2) what are the drivers of temporal change in these forests, and (3) how the spatial scale of observation influences studies of temporal change in forests? The dynamics of late-successional forests are far more complex than is commonly assumed. Between 1935-38 and 1976-85, beech density and basal area in high-elevation beech-dominated (>50% beech density) forests increased significantly. In 1993 beech bark disease (BBD) invaded and caused heavy mortality (as much as 90% of beech stems) in infected beech forests, but in disease-free forests beech dominance increased from 1976-85 to 2000-02, with beech basal area increasing nearly 30% on average. The demographic cause of the increase is the accretion of basal area in the largest trees, a pattern that does not fit common perceptions of late-successional forests. In contrast with trends in beech forests, the mixed species high-elevation deciduous forests exhibited a decline in tree density and basal area by forest type and disturbance history for most species from 1977-78 to 2002. Declines in tree density and basal area were strongly associated with soil chemistry, specifically low soil cation and high aluminum concentrations and were particularly high for northern red oak (Quercus rubra). The relatively high variance in density (nearly 35%) and basal area (> 25%) and the continued decline of basal area variance at grain sizes larger than 0.1 ha suggests that standard vegetation plots of this area do not capture the variance in forest attributes. Late-successional forests are complex systems whose temporal dynamics are not adequately described by current forest succession models. Temporal changes in the high-elevation deciduous forests of GRSM are influenced by historical and contemporary perturbations, the species composition of the forest, and the spatial scale at which change is observed.

Disturbance and long-term vegetation change in the high-elevation deciduous forests of Great Smoky Mountains National Park

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