Session I: Upland Plants

Abstract #: 97101

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EFFECTS OF HURRICANE ANDREW AND FIRE SEASON ON MORTALITY OF SOUTH FLORIDA SLASH PINES IN MIAMI ROCK RIDGE SAVANNAS: IMPLICATIONS FOR LONG-TERM VIABILITY AND MANAGEMENT OF NATURAL RESERVES

Robert F. Doren¹, William J. Platt², and Harold H. Slater^3
1 South Florida Natural Resources Center, Everglades National Park, 40001 SR 9336, Walt Dineen Homestead, FL 33034
² Louisiana State University, Department of Plant Biology, Baton Rouge, LA 70803-1705
³ Caribe Research Institute, 1034 Gibraltar Road, Key Largo, FL 33037


ABSTRACT
While natural disturbances have influenced the biota of the Everglades for centuries, anthropogenic disturbances are much more recent phenomena. This de novo combination of natural and anthropogenic disturbances constitutes a new environmental stress affecting ecosystems. In this study, we explore these interactions as they apply to reserve management using savannas dominated by south Florida slash pine (Pinus elliotti var. densa) as our model system. We also explore the interactions and relationships between Hurricane Andrew (the natural disturbance) and pre-hurricane fire regimes (potential anthropogenic disturbance) and their interactive effects on south Florida slash pine stands. We evaluated the effects of distance from the coast, size of the pine area, hydrology (as average depth to water by wet- and dry-season), time since last fire, size-class, and season of fire, on the mortality of pine. We sampled 15 sites within Everglades National Park (ENP) and southern Metropolitan Dade County (MDC) within the eyewall path of Hurricane Andrew, which crossed the tip of southern Florida on August 24, 1992. We assessed two types of mortality in each plot. Direct mortality included trees killed during the hurricane. Extended mortality resulted from deaths over the subsequent 24-30 months of trees still alive immediately after the hurricane (i.e., those not included as direct mortality). Results of our study indicate strong interactive effects on the pinelands, resulting from the combination of anthropogenic fire regimes and natural large-scale disturbances such as hurricanes. Both direct and extended mortality of pines were significantly higher in sites burned during the dry season than in sites burned during the wet season or unburned. Our analyses support the hypothesis that fire season (of the major environmental variables that could be accounted for) explains over 80% of the variability. These results indicate that anthropogenic alterations of fire regimes resulted in trees damaged by the hurricane becoming more susceptible to death from post hurricane stressors, possibly indicating that fire manipulation far outside normal regimes shifts environmental conditions away from those that occurred during the evolution of the species. The consequence of management of fire outside the natural season may mean the loss of significant portions of south Florida's slash pine savannas and has serious implications for management of natural reserves elsewhere.