Type of Document	Dissertation
Author	Passmore, Heather Alicia
Author's Email Address	hpassmo@lsu.edu
URN	etd-11102005-151604
Title	Effects of Hurricanes and Fires on Southeastern Savanna-Forest Landscapes
Degree	Doctor of Philosophy (Ph.D.)
Department	Biological Sciences
Advisory Committee	Advisor Name Title William J. Platt Committee Chair James P. Geaghan Committee Member James T. Cronin Committee Member Kam-Biu Liu Committee Member Lewis A. Gaston Dean's Representative
Keywords	plant ecology disturbance longleaf pine repeated measures analysis fire temperature fire intensity conceptual model decomposition fine fuel canopy photo prescribed fire
Date of Defense	2005-10-26
Availability	unrestricted
Abstract Sequential large-scale disturbances may produce interacting effects that differ from those predicted for each disturbance in isolation. These non-additive effects can strongly influence the composition and structure of plant communities. Hurricanes and natural lightning-season fires are large-scale, frequent disturbances in southeastern savanna-forest landscapes. Although interactive effects have been proposed, my research is the first to develop and experimentally test mechanistic hypotheses for hurricane-fire interactions. I develop a predictive conceptual model for interacting disturbances. I propose that hurricane-fire interactions depend on the relative timing of disturbances and the duration of effects. To predict the conditions under which hurricane-fire interactions are expected, my mechanistic hypotheses incorporate rates of fine fuel re-accumulation after a fire relative to decomposition of fine and coarse woody debris after a hurricane. This model suggests that the probability for disturbance interactions varies across savanna-forest landscapes. I predict that 1) hurricane-fire interactions are most likely in savannas, 2) they are least likely in forests, and 3) they may influence ecotones between savannas and forests by changing species composition and structure. Based on predictions, I implemented an experimental study in savanna-forest ecotone to test hypotheses of interactive effects. I hypothesized that effects of lightning-season fires differ when fires occur alone compared to when fires are preceded by hurricanes. I simulated two main effects of hurricanes as treatments– canopy disturbance and fine fuel deposition – by removing canopy trees and manipulating fuel loads. Compared to unaltered controls, I predicted hurricane treatments would influence fire intensity and vegetation response. Both canopy disturbance and fuel addition influenced the behavior of subsequent fires. In addition, the two main hurricane effects interacted to increase maximum fire temperatures. High fuel loads and fire resulted in disturbance interactions that reduced stem density and species richness of woody plants. Reduced hardwood density in areas of locally intense fires may decrease competition between species and increase establishment of pines and other fire-resistant species. Thus, hurricane-fire interactions influence vegetation structure in savanna-forest ecotones. Furthermore, over longer time scales interactions may result in landscape-level changes in southeastern savanna-forest ecosystems.
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