Spatial and temporal dynamics of a Costa Rican tropical dry forest

Long-term data from tropical dry forest communities are needed to understand the factors that influence tree species composition and forest dynamics, information critical to the conservation and management of this biome. The San Emilio tropical dry forest study area in the Area de Conservación Guanacaste (ACG), Sector Santa Rosa in northwestern Costa Rica offered the opportunity to investigate these unique tropical forests.; Chapter two is a study that describes the tree species abundance, composition and biomass of the San Emilio tropical dry forest based on over 30,000 individual trees that were mapped and measured in 1976 and 1996. During the 20 years, total stem density per ha decreased by 27%, yielding a forest-wide annual mortality rate of 3.52%. However, forest-wide annual recruitment was lower (3.05%), signaling that the forest was not in a steady state but was in a transitional phase. Above-ground forest biomass decreased by 3.5%, most likely caused by a long-term decrease in rainfall.; Chapter three investigates the effect of physical heterogeneity on the community dynamics of the San Emilio tropical dry forest. Analyses of vegetation surveys conducted in 1976 and 1996 showed that rates of change in stem density and biomass across the forest were related to variation in seasonal soil moisture and topography. The more xeric and highly variable areas showed the greatest change in stem density. The study suggests that the non-random heterogeneity found within the physical landscape of the San Emilio tropical dry forest contributed to local forest dynamics. Furthermore, on both spatial and temporal scales, these findings support previous work suggesting that neotropical dry forest dynamics are responsive to seasonal climates and the resulting microtopographic availability of soil moisture.; Chapter four explores the effects of heterogeneity on tree species and plant functional groups found in the San Emilio forest. While responding to this physical heterogeneity, the spatial and temporal variability in species abundance patterns reflect a forest on a successional trajectory that maybe affected by shifts in regional climate. (Abstract shortened by UMI.)...