Diversity, composition, and structure of tropical dry forests in Central America

Tropical dry forests have been reduced to less than 0.1% of their original expanse on the Pacific side of Central America and are considered by some t o be the most endangered ecosystem in the lowland tropics. Plots 1000 m(2) were established in seven tropical dry forests in Costa Rica and Nicaragua in order to compare levels of species richness to other Neotropical dry for est sites and to identify environmental variables associated with species r ichness and abundance. A total of 204 species and 1484 individuals greater than or equal to 2.5 cm were encountered. Santa Rosa National Park was the richest site with the highest family (33), genera (69), and species (75) di versity of all sites. Species richness and forest structure were significan tly different between sites. Fabaceae was the dominant tree and shrub famil y at most sites, but no species was repeatably dominant based on number of stems in all fragments of tropical dry forest. Central American dry forests had similar species richness when compared to other Neotropical forests. T here was no correlation between forest cover within reserves, or precipitat ion and plant species richness. There was a significant correlation between anthropogenic disturbance (intensity and frequency of fire, wood collectio n, grazing) and total species richness, tree and shrub species richness, an d liana abundance. These results suggest controlling levels on anthropogeni c disturbance within reserves should be a high priority for resource manage rs in Central America. Further research in forest fragments which examine i ndividual and a combination of disturbance agents would help clarify the im portance of anthropogenic disturbance on species richness and abundance.