Ecosystem Response

Results from field studies of Hurricane Hugo at various sites across the LUQ are summarized in this section. (For more details, see Walker et al. 1991, 1996.)

Damage patterns. Across the LUQ, wind damage was greatest on exposed northern slopes and in eastern sections closer to the hurricane track (Scatena and Larsen 1991). At El Verde, more than half of the trees were severely defoliated (56%), whereas some trees were snapped (11%) or uprooted (9%), though overall mortality was low (7%) (Walker 1991). At Bisley, aboveground biomass was reduced by 50%, and there were broad areas with 75-100% of trees blown down (Boose et al. 1994; Scatena et al. 1996). Nitrogen and phosphorus content in the leaf litter was about 30% and 100% greater at both sites, respectively, than prehurricane levels (Lodge et al. 1991).

Vegetation regeneration. Canopy cover was rapidly reestablished through re-leafing and sprouting of damaged trees and recruitment of pioneer species. Tree biomass and density decreased sharply and then returned to prehurricane levels, with no significant change in species richness. Aboveground net primary productivity rose and fell to prehurricane levels as a result of abundant regeneration of pioneer species. Temporary increases in light levels caused herb and woody seedling biomass to increase and then gradually decline. There was a transient rise and fall in forest floor biomass. Total fine litterfall decreased sharply and then increased, but did not reach prehurricane levels after 5 years. Fine root biomass decreased sharply, with little recovery after 5 years (Walker 1991; Zimmerman et al. 1994; Scatena et al. 1996; Zimmerman et al. 1996).

Soils and nutrient cycling. Soil temperature remained unchanged, and soil moisture increased only slightly. There were short-term increases in net N mineralization, net nitrification, and nitrous oxide fluxes, and short-term decreases in methane and carbon dioxide fluxes. There were also short-term increases in soil nutrient pools and nutrient concentrations in groundwater and streams that may have resulted from increased inputs, increased decomposition rates, increased leaching losses, and reduced nutrient uptake by biota. No significant change in soil organic matter was detected. High nutrient concentrations in pioneer species, reflected in increased aboveground pools of potassium and magnesium, helped to contain nutrient losses (Steudler et al. 1991; Scatena et al. 1996; Silver et al. 1996; Zimmerman et al. 1996).

Animal populations. Populations of many organisms declined immediately after the hurricane because of direct negative impacts on populations or because individuals migrated out of hurricane-damaged areas. Some populations increased and then returned to prehurricane levels because of improved resources, improved habitat, and/or a reduction in predator populations. Other populations declined sharply and then returned to prehurricane or above-hurricane levels, whereas still others declined with little recovery in 5 years (Waide 1991; Covich et al. 1996; Woolbright 1996; Zimmerman et al. 1996).

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