Summary of Ecosystem-Level Effects of Caribbean Hurricanes

Abstract

Effects of Hurricane Hugo on forest ecosystem processes in Puerto Rico and South Carolina are summarized from six research papers presented in this issue. Hurricanes are major catastrophic disturbances capable of altering ecosystemlevel processes in both the short and the long term. The high intensity, broad scale, and relatively high frequency of these storms makes them a major agent of catastrophic disturbance in the Caribbean and the Atlantic seaboard of the U.S.A. (Scatena & Larsen 1991). Although the return frequency of hurricanes for any given area is low (on the order of years or decades; Fig. 2 in Walker et al. 1991) relative to the lifespan of an individual investigator or a typical research project, the return time is shorter than the life span of a canopy tree or a forest ecosystem. Hurricanes have struck the Caribbean repeatedly within recorded history (Scatena & Larsen 1991, Walker et al. 1991), and have surely played a role in shaping plant population dynamics (e.g., Lugo et al. 1983), soil development (Scatena & Larsen 199 1) and nutrient cycling (Sanford et al. 199 1) over evolutionary time scales (thousands of years) in much of the Caribbean. Our paper summarizes the six preceding research papers in this issue, and focuses on the short-term changes in nutrient cycling induced by Hurricane Hugo, as well as the possible long-term consequences of such disturbances on tropical forests. Data on biomass and nutrient fluxes caused by Hurricane Gilbert in Quintana Roo, Mexico (Whigham et al. 1991, Plant Section, this issue) are included, but the discussion is primarily focused on two Long-Term Ecological Research sites funded by the National Science Foundation: the Luquillo Experimental Forest (LEF) in Puerto Rico and the North Inlet site in South Carolina. The processes summarized below are: hurricane litterfall and associated nutrient fluxes and exports; salinization of coastal soils from storm surge and associated changes in soil chemistry; fine root dynamics after disturbance; changes in soil nutrient pools and fertility; and, hurricane-induced changes in nitrogen (N) transformations and fluxes. DIRECT EFFECTS OF HURRICANE HUGO IN 1989, HURRICANE HUGO STRUCK NORTHEASTERN PUERTO RICO on 18 September with maximum sustained wind speeds of 166 kph, then struck the coast of South Carolina on 21 September with maximum sustained wind speeds of 217 kph. In addition, a storm surge associated with the hurricane inundated the coastal pine forest site in South Carolina. As a result of wind or wind plus salt stress, the forests were largely defoliated in both the Puerto Rican (Lodge et al. 1991, Walker 1991) and South Carolinian (Blood et al. 1991, Gardner et al. 1991) study sites. Consequently, a large amount of green leaves and wood were converted to necromass in all sites (Blood et al. 1991, Frangi & Lugo 1991, Lodge et al. 1991, Table 1). The forests in Quintana Roo, Mexico were similarly defoliated by winds of Hurricane Gilbert in 1988 (Whigham et al. 1991). In the LEF in Puerto Rico, the mass of fine litter resulting from Hurricane Hugo was ca 1000 g/m2 in tabonuco and palm forests, and 625 g/m2 in dwarf forest (Table 1, Lodge et al. 1991). The mass of litterfall resulting from Hurricane Hugo was 1.2 to 2.0 times the mean annual litterfall inputs in the LEF. In Mexico, Hurricane Gilbert induced a litterfall of 836 g/m2 leaves and 1600 g/m2 wood (Table 1; Whigham et al. 1991). In addition, wind structurally damaged or killed some of the trees in Puerto Rico (Frangi & Lugo 1991, Walker 1991), and South Carolina (Gardner et al. 1991). Damage to root systems was also apparent in both sites, though it is unclear to what extent the physical damage resulting from wind or salt stress was exacerbated by the drought of several months that followed the hurricane (Blood et al. 1991, Parrotta & Lodge 1991). ECOSYSTEM RESPONSES TO HURRICANE HUGO NUTRIENT CYCLING.-A large pulse of litterfall containing higher than normal concentrations of certain nutrients and labile carbon was deposited in all sites i Received 5 July 1991, revision accepted 15 July 1991.