Estimativas de biomassa lenhosa, estoque e seqüestro de carbono acima do solo ao longo do gradiente de inundação em uma floresta de igapó alagada por água preta na Amazônia Central

Abstract

Floodplain forests play an important role in the biogeochemical cycles. However, little is known about the amount of carbon that these forests are able to store. In this study, we estimate aboveground woody biomass, carbon stock and sink, and residence time of carbon in biomass in three flooding levels of the black-water igapó forests of the Amanã Sustainable Development Reserve, Central Amazonia. Additionally, dendrochronological methods were applied to determine forest age, annual radial increment and wood density of tree species in the different levels of inundation. To collect data, we used 11 625-m2 plots where all trees with DBH ≥ 10 cm were identified and measured in DBH and height. Estimates were made by using allometric regression models which take into account different variables of vegetation. We observed a change on floristic composition and an increase on species richness along the gradient of inundation. However, with the exception of tree height that was larger in the high igapó (smaller flooding time), low, middle and high igapó forests did not differ in terms of DBH, age, annual radial increment, and woody density. Forests were estimated to be between 261 and 337 yrs-old, being considered as mature forests. Of the six allometric equations evaluated, only the three which consider simultaneously the parameters DBH, woody density and tree height estimated similar values of woody biomass and carbon stock. In average, low igapó presented biomass of 180 Mg/ha, which is significantly fewer than middle and high igapós (232 and 229 Mg/ha, respectively). The same was found for carbon stock, which was respectively 90, 116 and 115 Mg C/ha in the low, middle and high portions. We observed a tendency of increase on carbon sink from 1.2 in the low portion to 2.0 Mg C/ha/year in the high portion, but mean residence time of carbon did not differ significantly among igapós (54, 57 and 78 years). Compared to high productive várzeas, the igapós of Amanã present a slow growth dynamic and therefore a low potential for timber exploitation. Further studies evaluating growth in species level are required to a better understanding of the carbon dynamics of this igapó.