Longleaf pine (Pinus palustris) is one of the better-known disturbance-maintained ecosystems, and its dependence on fire is both well studied and understood. It is also somewhat of a biodiversity paradox in that longleaf pine is typically the sole overstory species, but numerous species comprise the herbaceous layer. Because its natural range—widespread throughout the southeastern United States—coincides with the region of North America that experiences highest frequencies of landfall tropical cyclones, however, another disturbance regime of great significance is that of tropical storms and hurricanes. A phenomenological model has been developed that integrates both disturbances in influencing the physiognomy of longleaf pine stands. Tropical cyclones influence the overstory directly via wind-caused damage and mortality, influencing the herbaceous layer indirectly by altering the spatial distribution of litter accumulation and competition. By contrast, fire exerts effects on juvenile pine stages directly, with indirect effects on the herb layer via fine fuel consumption and selective mortality of potentially competing plants. This paper examines the dynamics of tropical cyclone meteorology and climatology in the context of potential effects on longleaf pine ecosystem and implications for climate change.
Tropical cyclones are among the more destructive forces in nature. As dramatic an event as was the 1980 eruption of Mt. St. Helens (Washington State, United States), its total energy yield was 1,000 times lower than that of a typical tropical cyclone. In contrast to their threats to human populations, which includes both high winds and flooding, wind damage is the primary threat for longleaf stands. Tropical cyclones are formed from a complex combination of meteorological conditions, driven initially by the release of excess heat from the surface waters of the ocean, along with an unstable atmosphere of air temperatures decreasing and wind speeds increasing with altitude. Sea surface temperature (SST) is of particular importance, as higher SSTs indicate a higher heat content of surface ocean water, resulting in release of more heat energy. Evidence is quite clear that SSTs have increased in the Northern Hemisphere from the mid-1970’s to the present. Consistent with this pattern are increases in frequency and intensity of tropical cyclones. Although the degree to which the current scenario for tropical cyclones represents a future threat to longleaf pine ecosystems in general is unknown, tropical cyclones no longer occur within the constraints previously suggested by “natural disturbance” models that emphasize the historical role of cyclones in the natural physiognomy of longleaf pine ecosystems.
