A Quantitative Phytogeographic Analysis of Species Richness in Forest Communities of the Paraná River Delta, Argentina

A biogeographic analysis of 26 species of trees and shrubs occurring in the Paraná River Delta (32 ° to 34 ° 30′ South latitude, 58 ° to 61 ° West longitude, Argentina) was performed to study the floristic and structural differences among deltaic woodland communities. Traditionally these variations have been interpreted as a consequence of the differential influence of local island geomorphology and flood dynamics on floristic successions. We performed a cluster analysis of collection site, obtained maps showing the joint occurrence of the species of each community, and related species ranges with the presence of possible migration corridors. Results suggest that, in addition to local variations in topography and flood persistence, changes in floristic richness can be understood as a consequence of the differential efficiency of the Paraná and Uruguay Rivers as migration corridors for tropical species into temperate latitudes. Geomorphical stability of riverbeds and fluvial dynamic differences between rivers are discussed in relation to how they may explain the more efficient migration of species along the flood plain of the Uruguay River compared to the Paraná River. Results allows us to re-interpret the relative importance of both rivers in the establishment of tropical and subtropical species in temperate latitudes, and to add a regional explanation for the observed floristic heterogeneity.