Variation in forest structure and carbon dynamics in tropical rain forests of Amazonia

A better understanding of the variations in the dynamics and structure of trees in tropical forests is necessary for predicting the potential for these ecosystems to lose or store carbon. Data from forest inventory plotsshow large differences in forest structure, biomass, and tree growth rates among plots in three location. The number of stems (g.t. 10cm diameter)per hectare is higher in the Manaus site (626 ha^-1) than in the Rio Branco (466 ha^-1) or Santrem (460 ha^-1) sites. Stocks of C in above-ground biomass in the three areas were 180.1 (Manaus), 122.1 (Rio Branco), and 140.6 (Santarem) MgC ha^-1. Estimates of mean annual accumulation of C in living trees based on monthly dendrometer band measurements ranged from 1.6 (Manaus), 2.5 (Rio Branco), to 2.8 (Santarem) MgC ha^-1 yr^-1. Our results showed marked seasonality to growth, with highest growth rates in the wet and lowest rates in the dry season. This effect was most pronounced for trees with diameter g. t. 50cm. Comparing the three areas investigated suggests that forests experiencing a longer dry season have larger annual diameter growth increments for individual trees, and more of the forest biomass in the largest trees.