Distribution and abundance of arboreal species in the atlantic ombrophilous dense forest in Southeastern Brazil

The relative densities of arboreal species of 17 surveys carried out in the Atlantic Ombrophilous Dense Forest of Sao Paulo state, SE Brazil, were compared by means of multivariate analysis (cluster, TWINSPAN, PCA, DCA and CCA) to assess floristic and structural variation. The arboreal flora of this vegetation formation is heterogeneous: out of the 771 specific binomials cited, 478 were recorded only once. As the results were similar whether these 478 species were included or not, they were therefore excluded from subsequent analyses. The cluster analysis and TWINSPAN recognised two floristic-structural groups: Coastal Province and Atlantic Plateau. The DCA resulted in a gradient related to distance from the sea, from the Coastal Province towards the Atlantic Plateau (lambda (1)=0.6944). The CCA confirmed this separation on the first axis (lambda (1)=0.6944; 12.7% of total variance; p <0.01) and showed this gradient to be associated with altitude and latitude on one hand and temperature and precipitation on the other. The influence of latitude and longitude was weak. Although surveys used different criteria, only the minimum individual size adopted in sampling showed a weak influence on the second axis on the CCA (lambda (2)=0.4437; 8% of total variance), and sampling method showed no influence. A positive relationship between geographical distance and floristic-structural dissimilarity was detected by the Mantel test (Z(obs)=0.320; Z(ave)=0.300; p <0.001). The predominance of arboreal species of restricted distribution and the great spatial variation of abundance would appear to indicate narrow niches. The occurrence of complex and non-linear gradients suggests the importance of several other abiotic features in the spatial distribution and abundance of arboreal species in the Atlantic Ombrophilous Dense Forest in the state of Sao Paulo.