Sub-regiões fitogeográficas da floresta atlântica entre as bacias dos rios São Francisco e Uruguai baseadas na análise dos padrões de distribuição espacial da flora arbórea e do clima / Phytogeographic subregions of the Atlantic Forests between São Francisco and Uruguay River basins based on the analysis of spatial distribution patterns of the tree flora and climate

Arthur Sérgio Mouço Valente

The spatial variation in the composition of the tree flora of some Atlantic forest areas distributed in the East Atlantic basins, Southeastern and Southern Brazil, extended to Paraguay and Argentina, was investigated under four main aspects: (1) to evaluate the level of floristic differentiation of tropical and subtropical forests along their latitudinal, altitudinal and inland gradients; (2) to propose and circumscribe phytogeographic subdivisions for the region based on variations in the composition of the dendroflora and physiognomic features of the forests; (3) to evaluate the heterogeneity of the tree flora pondering the influence of spatial and environmental variables; (4) to indicate the main climatic factors that characterize the phytogeographic subregions. The dataset includes 589 organized forest areas in an environmental database, containing geographical and bioclimatic records and a floristic database, containing binary records for the presence of 3,669 species, 632 genera and 117 families. Multivariate analyses (CCA, DCA, PCoA, CRT, TWINSPAN, ISA, cluster analyses and dissimilarity indexes) were used to search for the distribution of emerging patterns and interrelationships in the dataset. The set of tree species represents 24% of the estimated vascular plants for the Atlantic Forest. There were three times more rare species of trees in the 100 km closer to the sea. The tropical forests tend to have the richest flora and with greater occurrence of unique species, however there is a clear reduction of species richness in the subtropical subregions. Although this reduction is also reported in the level of internalization, this did not occur in a homogeneous pattern among subregions in none of the latitudinal and altitudinal gradients. The floristic heterogeneity is evidenced in the description and in the relationship among the eleven phytogeographic subregions which represent subsets of the tree flora. There are five rain subregions where two are typically tropical coastal plains and five seasonal inland subregions and more the mixed Araucarian forests. The results have added a contribution to the knowledge of the phytogeographic differentiation of the Atlantic Forest trees sensu lato to the South of São Francisco River basin. It is possible to maintain a high correlation between phytogeographic and phytophysiognomic classifications and those with the climate.

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