PARENT SESSION
Oral Session # 96: Disturbance Ecology: Wind and Water.
Presiding: L Battaglia
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 202.

Hurricane disturbances, tree species diversity, and succession in North Carolina Piedmont forests.

Xi, Weimin^*,1, Peet, Robert K.¹, Urban, Dean L.², ¹ University of North Carolina at Chapel Hill, Chapel Hill, NC, USA² Duke University, Durham, NC, USA

ABSTRACT- Windthrow has been hypothesized to play a critical role in maintaining species diversity in temperate deciduous forests. Recent work by Beckage and Clark has shown that large canopy gaps maintain tree diversity in southern Appalachian forests. However, few long-term data are available for assessing the importance or generality of disturbance-maintained tree species coexistence. We have used long-term tree (stems >1 cm dbh) demographic data to assess the effect of Hurricanes Hazel (1954) and Fran (1996) on tree species diversity and tree replacement in North Carolina Piedmont forests. In addition, we used understory sapling (stems > 1m tall and < 1 cm dbh) growth and survival data to project post-hurricane changes in canopy composition. Our results support the hypothesis that large wind disturbances help to maintain local tree species diversity. Although there is often an immediate drop in diversity following hurricane damage, species diversity of saplings quickly increases to levels that typically exceed those prior to the disturbance.This typically leads to an increase in tree species diversity (sometimes by as much as a factor of two) in substantially damaged stands. Nonetheless, time-series analysis showed that hurricanes significantly decrease the dominance of several important, shade-intolerant canopy species such as oaks and hickories owing to lack of advanced regeneration in the understory, while increasing the dominance of pre-established, shade-tolerant species such as red maple. We conclude that large, infrequent wind disturbances help to maintain local tree diversity, but also accelerate the increase in dominance of red maple. This pattern may widely apply in the Piedmont region and adjacent temperate forests regions of the eastern United States.

Key words: tree species diversity, Piedmont forests., wind disturbance, tree demography