Hurricane-fire interactions: testing predictions in the savanna-forest landscape.
Passmore, Heather*,1, Platt, William1, 1 Louisiana State University, Baton Rouge, LA
ABSTRACT- Sequential large-scale disturbances may produce interacting effects that differ from those predicted for each disturbance in isolation. These non-additive effects can influence the composition and structure of plant communities. Hurricanes and lightning-season fires are large-scale, frequent disturbances in southeastern savanna-forest landscapes. We generated predictions with a conceptual model of hurricane-fire interactions, then tested these predictions with an experimental study using simulated hurricane disturbance followed by prescribed fire. Based on our model, we predicted that the probability for hurricane-fire interactions varies across savanna-forest landscapes. Specifically, 1) hurricane-fire interactions are most likely in savannas, 2) they are rare in forests, and 3) they are unpredictable in ecotones between savannas and forests. We expected that interactive effects may change the composition and structure of plant communities in ecotones. We tested the hypothesis that in ecotones, effects of lightning-season fires on plant communities would differ when fires occurred alone compared to when hurricanes preceded fires. We simulated two main effects of hurricanes as treatments – canopy disturbance and fine fuel deposition – by removing canopy trees and manipulating fuel loads. Relative to controls, high fuel loads and hotter fires in treatment plots reduced both stem density and species richness of woody plants. Reduced hardwood density in areas of locally intense fires may ultimately decrease competition between species, and increase establishment of pines and other fire-resistant species. These results indicate that hurricane-fire interactions influence vegetation structure in savanna-forest ecotones. Over longer time scales, these interactions may result in landscape-level changes in southeastern savanna-forest ecosystems.
Key words: hurricane-fire interaction, longleaf pine savanna, disturbance ecology
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