The original forest cover in Rio Grande do Sul is strongly reduced and fragmented and, particularly on Serra do Sudeste, little is known about the structure of its forests. The finding of a primary forest remnant in the oriental slopes allowed a phytosociological survey that aims to describe the structure of the arboreal component and to establish its relations with other seasonal forests. All trees with DBH > 5 cm were recorded in an area of 1 ha, subdivided into 100 plots of 10 × 10 m. On the phytosociological survey 2.236 individuals were sampled, belonging to 69 species, 55 genera and 34 families. Myrtaceae, Lauraceae and Euphorbiaceae were the families with the highest species richness. Fabaceae almost do not appear in forests of Serra do Sudeste, which is contrasting with its participation in other seasonal forests in southern Brazil. Among the species with the highest importance values, some were found in high density, as Gymnanthes concolor Spreng., Esenbeckia grandiflora Mart. and Sorocea bonplandii (Baill.) W.C.Burger et al. Other species presented high values of basal area, as Sloanea monosperma Vell. and Ilex paraguariensis A.St-Hil. Some species showed intermediate values for the estimated parameters, such as Myrsine umbellata Mart., Miconia rigidiuscula Cogn., and Calyptranthes grandifolia O.Berg. Species diversity (H') was estimated as 3.204 (nats) (J' = 0.757), one of highest values recorded for seasonal forests in Rio Grande do Sul, in the same diversity context found for this formation elsewhere in Brazil.
arboreal diversity; phytogeography; phytosociology; seasonal forest; southern Brazil
