Late twentieth-century trends in tree-community composition in an Amazonian forest

Abstract

The rainforests of central Amazonia are some of the most species-rich tree communities on earth. In recent decades, forests in the central-Amazonian landscape have experienced highly non-random changes in dynamics and composition. These analyses are made on a network of eighteen permanent plots unaffected by any detectable disturbance. Within these plots, tree mortality, recruitment, and growth have increased over time. Of 115 relatively abundant tree genera, twenty-seven changed significantly in density or basal area - a value nearly fourteen times greater than that expected by chance. An independent, eight-year study in nearby forests corroborated these shifts in composition. Despite increasing tree mortality, pioneer trees did not increase in abundance, but genera of faster-growing trees, including many canopy and emergent species, are increasing in dominance or density, whereas genera of slower-growing trees, including many subcanopy species, are declining. Rising atmospheric CO2 concentrations may explain these changes, although the effects of this and other large-scale environmental alterations have not been fully explored. These compositional changes could have important effects on the carbon storage, dynamics, and biota of Amazonian forests. © Oxford University Press 2005. All rights reserved.