Variation in floristic composition, demography and above-ground biomass over a 20-year period in an Amazonian monodominant forest

Background: Previous work has shown that Amazonian tropical forests have experienced two widespread changes in dynamics over recent decades, increases in both tree stem turnover and above-ground biomass. However, data from an Amazonian monodominant forest dominated by Peltogyne gracilipes have shown that the above-ground biomass of this forest type has declined slightly (<5%) over an 11-year period. Aims: To determine whether the tree communities in three types of forest, with or without Peltogyne gracilipes (Peltogyne-rich forest (PRF), Peltogyne-poor (PPF) and forest without Peltogyne (FWP)) on Maraca Island, Roraima, have experienced a change in structure and floristic composition over a 20-year period. Methods: We have quantified the variation in the occurrence and abundance of tree species, the above-ground biomass (AGB) and change in total stand biomass from mortality, recruitment and growth for trees, palms and large lianas, >= 10 cm diameter at breast height, in three plots of 0.25 ha in each of the three forest types. Results: Floristic composition showed little change, with no shift in the rank abundance amongst the 10 most important tree species, although in FWP there was a reduction in species richness from 51 to 43. Recruitment is shown to offset the losses caused by mortality in PRF and FWP. The annual mean mortality rates were low, at around 1%. In 2011 AGB in the three forest types varied from 434 Mg ha(-1) (PPF) to 363 Mg ha(-1) (FWP). PRF experienced an AGB decline of 4.1%, associated with the death of large trees, while FWP showed a slight increase in biomass (2.6%). Conclusions: Over the last 20 years Maraca forest stands appear to have been stable in terms of their floristic composition and structure, some showing a persistent monodominance by Peltogyne gracilipes.