Collections > Electronic Theses and Dissertations > Forest response to natural disturbance: changes in structure and diversity on a North Carolina Piedmont forest in response to catastrophic wind events
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Large hurricanes have profound impacts on temperate forests, but owing to their infrequent nature these effects rarely have been examined in detail. In 1996 Hurricane Fran significantly damaged many long-term census plots in Duke Forest in Piedmont North Carolina, thereby providing a unique research opportunity. I combined over 20 years of pre-hurricane and five years of post-hurricane data on individual trees, seedlings and saplings to determine how hurricanes affect forest structure, diversity, and succession. Several plots severely damaged in 1954 by Hurricane Hazel allowed comparison of recovery patterns and evaluation of long-term effects. I first assessed hurricane-induced structural and compositional changes and evaluated mortality risk factors. Fran caused widespread uprooting of large canopy trees. Stand-level damage severity varied substantially across the distributed network of permanent plots. Hurricane-induced mortality of large-size hardwoods was often delayed. Although tree damage was primarily caused by winds and rainfall, damage was also found to be correlated with site exposure, topographical position, tree size, and species susceptibility to wind. Next, to test the hypothesis that hurricanes maintain local tree diversity through increased heterogeneity and resource availability I examined changes in understory survivorship, recruitment, and growth. The understory experienced highly variable population impacts as well as subtle changes in tree diversity. Following Fran both seedlings and saplings exhibited an immediate drop in stem density followed by a rebound. In addition, the hurricane resulted in release of established, shade-intolerant or mid-tolerant seedlings and saplings, thereby potentially increasing future canopy tree diversity. Finally, I assessed whether hurricanes have long-term effects on tree diversity and succession. Past hurricanes appear to have accelerating succession in even-aged pine stands toward a later, hardwood-dominated successional stage, and to have shifted the hardwood forests toward more diverse composition, although with increasing dominance of red maple. I concluded that large, infrequent hurricanes play an important role in shaping forest structure and maintaining tree diversity in the Piedmont region. However, the effects on tree composition and diversity vary greatly and depend on local damage severity, pre-hurricane stand characteristics, and the temporal and spatial scales at which the changes are observed.