MAINTENANCE OF RAIN-FOREST DIVERSITY IN RIPARIAN FORESTS OF TROPICAL SAVANNAS - IMPLICATIONS FOR SPECIES CONSERVATION DURING PLEISTOCENE DROUGHT

Structural and floristic attributes of riparian forest patches in a Neotropical savanna were studied in order to evaluate their potential to maintain rain forest plant diversity during periods of drought. Tree density was significantly greater, and basal area significantly lower, than pantropical means for these variables, thus these riparian forests were characterized as low biomass, many-stemmed communities. A total of 292 species greater than or equal to 0.5 m high were found in an aggregate vegetation sample of 1.6 ha. Most species were typical rain forest taxa, indicating that this flora is not specialized to the riparian environment. Isolation of these patches was found to have some negative effects on species composition, since dioecious and mammal dispersed species were more poorly represented in riparian than in continuous forests. While this riparian system is not floristically depauperate, species densities in individual plots indicate that its richness is comparable to that of continuous forests in Central America. These results suggest that tropical riparian forest fragments have the potential, albeit limited, to maintain large numbers of rain forest species and, thus, that analogous forest fragments may have played an important role as safe sites for tropical rain forest floras during periods of drought in the Pleistocene.