ABSTRACT Upper montane ecosystems in Brazil are little known, and their structural and functional aspects poorly understood. Our goals were to describe tree species diversity and community structure, and to characterize tree species in relation to their ecological traits, phytogeographic history and conservation status in an upper montane araucaria forest remnant. A total of 26 species belonging to 18 families were found in a 1-hectare permanent plot. The tree community mainly comprised trees with diameters of less than 20 cm and heights of between 6.5 and 9.5 m. Drimys angustifolia and Myrceugenia regnelliana had the highest importance values. Most species were shade tolerant while most individuals were pioneers. Most species and individuals presented zoophily and zoochory. Most sampled species and individuals were related to araucaria forests. Seven species are threatened to some degree while one species, Crinodendron brasiliensis, besides threatened, is also endemic to the region. The presence of endemic and endangered species demonstrates that the studied area serves important conservation purposes. Furthermore, the present study demonstrates the important role that upper montane regions have for conservation and describes the structural patterns of still poorly studied habitats, reinforcing the importance such systems have in maintaining species diversity at high elevations.

Este estudo objetivou determinar a distribuição espacial das espécies arbóreas mais abundantes num remanescente florestal e avaliar relações que possam ser responsáveis por estas distribuições, bem como comparar a riqueza específica esperada ao longo da formação Serra Geral no estado do Rio Grande do Sul, Brasil. Uma parcela de 1 hectare, subdividida em 100 unidades amostrais contíguas foi instalada e todos os indivíduos com pelo menos 4,8 cm de diâmetro à altura do peito foram medidos e identificados. Cada unidade amostral recebeu uma descrição de sua posição espacial por meio de coordenadas (x,y) para quantificar o padrão espacial e posteriormente aplicar um índice de associação para as espécies amostradas. A riqueza específica foi comparada a outros levantamentos realizados na região da encosta da Serra Geral do estado do Rio Grande do Sul por meio de rarefação. Foram amostrados 1.063 indivíduos distribuídos em 69 espécies e 33 famílias. A diversidade especifica foi de 3,35 nats (equitatividade Pielou - J' = 0,79) e a maioria das espécies apresentou distribuição agregada. Padrões de associação e dissociação foram encontrados entre as espécies, demonstrando diferentes grupos florestais. Foi observado que existe um decréscimo de espécies Atlânticas no sentido leste para oeste na formação Serra Geral, sendo substituídas por espécies da floresta estacional.

This study aimed to determine the spatial distribution of the most abundant tree species, to look for relationships that may be responsible for their distribution and to compare the expected richness along the Serra Geral formation in the state of Rio Grande do Sul , Brazil. An one-hectare plot was divided in 100 contiguous 10 x 10 m sampling units and all individuals with at least 4.8 cm diameter at breast high were measured and identified. Each sampling unit received a description of the spatial position through metric coordinates (x,y) in order to quantify the spatial pattern. Later, an association index among species was applied. The observed richness was rarefied and compared to other surveys located on the slopes of Serra Geral in Rio Grande do Sul. We surveyed 1,063 individuals belonging to 69 species and 33 families, and the Shannon's diversity index showed a diversity of 3.35 nats (Pielou's species evenness - J' = 0.79). Most species showed an aggregated distribution. Both association and dissociation patterns occurred among species leading to distinct forest patches. The rarefaction results showed a decrease of Atlantic species, which were replaced by typical seasonal forest species, when analyzing floristic contingents towards the west.