Hurricanes have a profound effect on many coastal ecosystems. Direct impacts often include wind damage to trees, scouring and flooding of river channels, and salt-water inundation along shorelines (Simpson and Riehl 1981; Diaz and Pul-warty 1997). In some areas, secondary impacts may include landslides triggered by heavy rains (Scatena and Larson 1991) or catastrophic dry-season fires resulting from heavy fuel loading (Whigham in press). This chapter will focus on the long-term impacts of hurricane wind damage at two LTER sites, the Harvard Forest (HFR) in central New England and the Luquillo Experimental Forest (LUQ) in northeastern Puerto Rico. These two sites, both located in the North Atlantic hurricane basin and occasionally subject to the same storms, provide interesting examples of tropical and temperate hurricane disturbance regimes.

Wind damage from a single hurricane is often highly variable (Foster 1988). Damage to individual trees can range from loss of leaves and fine branches, which can significantly alter surface nutrient inputs (Lodge et al. 1991), to bole snapping or uprooting, which can significantly alter coarse woody debris and soil microto-pography (Carlton and Bazzaz 1998a and b). At the stand level, damage can range from defoliation to individual tree gaps to extensive blowdowns, creating different pathways for regeneration (Lugo 2000). At landscape and regional levels, complex patterns of damage are created by the interaction of meteorological, topographic, and biological factors (Boose et al. 1994).

Adding to this spatial complexity is the fact that successive hurricanes are not necessarily independent in terms of their effects. A single storm lasting several hours may have effects that persist for decades (Foster et al. 1998). And forest sus ceptibility to wind damage is strongly influenced by composition and structure, which in turn are strongly influenced by previous disturbance history (Foster and Boose 1992). Thus, the impacts of a single hurricane may depend in part on the impacts of earlier storms as well as on other previous disturbances and land use. Hurricanes, like other disturbances, both create and respond to spatial heterogeneity (Turner et al. 2003).

To understand the long-term ecological role of hurricanes at a given site, we must consider these three sets of questions: (1) What is the hurricane disturbance regime? How do the disturbance events (hurricane wind damage) vary in space and time? (2) What is the ecosystem response to a single event? How does ecosystem response vary with disturbance intensity? (3) What is the ecosystem response to repeated events? How does hurricane disturbance fit into the overall disturbance regime? This chapter will highlight recent studies by the Harvard Forest and Luquillo LTER programs, focusing on the reconstruction of past hurricanes (first questions), summarizing results from field studies of ecosystem response to wind damage (second questions), and outlining possible directions for future research (third questions).

0 0

Post a comment