Floristic composition and structure of tree community on the transition Lowland - Lowermontane Ombrophilous Dense Forest in Nucleo Picinguaba/Serra do Mar State Park, Ubatuba, southeastern Brazil

We conducted floristic and structural surveys on arboreous component (circumference at breast high >= 15 cm) in 1 ha plot (100 sub-plots of 10 x 10 m) located in a stretch of Atlantic Ombrophilous Dense Forest Lowland-Lower montane transition, in Nucleo Picinguaba/PESM, Ubatuba, Sao Paulo State. The regenerating layer (H >= 1.5 m and circumference at breast height < 15 cm) was sampled in 0.4 ha (40 sub-plots of 10 x 10 m) within the plot. The richness and diversity were 156 species and H' = 4.00 for the arboreous component in I ha, 173 and H' = 4.25 for arboreous (113 species) and regenerating (134 species) layers together in 0.4 ha, and 192 species considering the whole sample. The most abundant species in the tree layer were Euterpe edulis, with 191 individuals (14.8%), Mollinedia schottiana (5.1%), Rustia formosa (4.8%), Chtysoplhyllum flexuosum (4.7%), Coussarea meridionalis var. porophylla (4.7%) and Guapira opposita (4.4%). These species were also among the most abundant in the regenerating layer. The richest families were Myrtaceae (32 spp.), Rubiaceae (15), Fabaceae (13), Sapotaceae (10), Moraceae (eight), Euphorbiaceae (seven) and Lauraceae (six). Tree species richness varied positively with density along the vertical structure of vegetation, being higher in lower high classes, where the density is much larger. On the other hand, the evenness in these classes was lower, increasing toward the upper classes, where trees are not concentrated in few species.