The objective of this study was to describe the changes in the floristic composition and community structure of the tree-shrub layer in the valley forest in the Chapada dos Guimarães National Park in Mato Grosso State, Brazil. The data were collected in three parallel transects, systematically distributed and equidistant on both sides of the stream. The tree layer (diameter at the breast height > 5 cm) was surveyed in 1996 and 1999 in 18 plots of 600 m² each. The saplings (diameter at the breast height > 1 cm and < 5 cm) and juveniles (total height > 30 cm and diameter at the base of at least < 1 cm) were surveyed in 1999 and 2001 in 36 plots of 50 and 6 m² respectively. The high species richness, a total of 212 species, was probably due to the inclusion of saplings and juveniles along with the tree layer. The change in floristic composition was small and gains and losses were limited to those species with low abundance (< 3 individuals). These changes did not reflect significant changes in diversity. The size distribution, height and diameter, did not differ between sampling dates indicating a relative stability in this forest. However the apparent floristic and community stability should not be interpreted as indicating that the forest is at climax since changes are occurring in both time and space.
community dynamics; demographic changes; diversity changes; floristic changes
