Seed and Seedling Bank Dynamics in Secondary Forests Following Hurricane Georges in Puerto Rico TERESITA LOMASCOLO 1 AND T. MITCHELL AIDE Biology Department, University of Puerto Rico, P.O. BOX 23360, San Juan, Puerto Rico 00931-3360. 1 Corresponding author, present address: Laboratorio de Investigaciones Ecolo´gicas de las Yungas (LIEY), Universidad Nacional de Tucuma´n, C.C. 34 Yerba Buena (4107), Tucuma´n, Argentina. liey@tucbbs.com.ar. tmaide@yahoo.com ABSTRACT.—This study describes the effect of Hurricane Georges (September, 1998) on the dynamics of seed and seedling banks in young secondary forests (25 yr) and mature secondary forests (60 yr) in aban- doned pasture lands in Puerto Rico. In eight secondary forest sites, the seed bank was sampled in July 1998 and July 1999, and the seedling bank was sampled in November 1998 and November 1999. We collected data on number of species and individuals. In the seedling bank, mortality, recruitment and growth rate were estimated for one year. Hurricane damage was estimated for each site. The data suggest that sites in early stages of succession receive less damage from hurricane-force winds than older sites. As a consequence, after a hurricane later stages of succession present high light conditions, which result in high growth rate of pioneer and non-pioneer species. Although high light conditions may enhance seed germination from the seed bank, recruitment was low, and most post-hurricane regeneration came from pre-established individu- als in the seedling bank. The recovery of secondary forests is usually studied in reference to time since abandonment, but this study shows that natural disturbances, particularly hurricanes, can affect the succes- sional trajectory of secondary forests. INTRODUCTION Disturbances play an important role in structuring all natural communities, al- though ecosystems have different distur- bance regimes depending on their geo- graphic location and vegetation type. For example, while fire maintains community structure and function in most shrublands (Christensen, 1985), hurricanes influence plant and animal communities, as well as ecosystem processes in the Caribbean (Tan- ner et al., 1991). Hurricanes play a major role in influenc- ing the composition and structure of Car- ibbean plant communities. Hurricane-force winds cause defoliation, limb loss, and tree uprooting or snapping that change canopy cover and increase light availability in the understory. An additional effect is the pulse of nutrients associated with the enor- mous deposition of litter (Frangi and Lugo, 1991; Lodge et al., 1991), which may affect seedling bank dynamics (Guzma´n-Grajales and Walker, 1991). Human pressure is ob- viously another important source of distur- bance. Most of the original forest in Puerto Rico was cleared for agriculture, but large tracts were subsequently abandoned, re- sulting in large areas of secondary forest. The recovery of these forests is usually studied in reference to time since abandon- ment, although natural disturbances, par- ticularly hurricanes, can affect their normal successional trajectory. On September 21, 1998, Hurricane Georges struck Puerto Rico, and it was the most destructive hurricane since San Cipri- ano (1932). Hurricane Hugo (1989) had stronger winds but affected a small portion of the island. Hurricane Georges entered the island from the southeast and traversed it from east to west. Maximum sustained winds were 177 km/h and the eye was 40- 48 km wide (National Weather Service Re- port). Virtually the whole island was af- fected by hurricane-force winds. At the time of the hurricane, we had been working in the study area for three months studying the recovery of species interactions during secondary succession. The pass of the hur- ricane gave us the opportunity to study the effect of this natural disturbance in second- ary forest dynamics, and we used the pre- Caribbean Journal of Science, Vol. 37, No. 3-4, 259–270, 2001 Copyright 2001 College of Arts and Sciences University of Puerto Rico, Mayagu¨ ez 259