Estoque de carbono de palmeiras arborecentes em diferentes tipos de florestas do ecótono norte da Amazônia Brasileira: efeitos das condicionantes ambientais

Abstract

The palms (Arecaceae) comprise one of the most important botanical families in the Amazon, with a wide distribution, abundance and large potential for the carbon dioxide removal (CO2) from the atmosphere. However, few is known about their real contribution because it is generally excluded from the estimates or considered as trees in the calculations. This study has as objective determinate the carbon stock in large palms that exist under different environmental constraints in the Brazilian Amazon’s northern ecotone forests, pinpointed at a savanna-forest contact zone of Roraima State. Therefore, a forest inventory was conducted in 129 plots of 10mx50m (6.45ha). Palm individuals were quantified associated with their respective species and measured their DBH (Diameter at Breast Height), total and stipe heights. Environment constraints were analyzed: edaphic factors (texture – sand percentage; and fertility – bases sum, cation exchange capacity and Fe+2 concentration), drainage type and canopy opening. Abundance, basal area and biomass were considered ecological descriptors and reduced individually by a multivariate analysis (PCA - Principal Component Analysis). ANOVA (Analysis of Variance) was performed to verify the existence of significant differences between structural parameters data of which species and the three types of forests considered (ombrophilous, semideciduous seasonal and deciduous seasonal forests), should differences occur, Tukey test was performed. A generic ordaining analysis based on environment constraints and abundance of individuals. The carbon stock was calculated from models derived from scientific literature to family, genus and specific for trees. Two-hundred thirteen individuals of large palms were observed, belonging to five species (Astrocaryum aculeatum, Euterpe precatoria, Mauritia flexuosa, Attalea maripa e Oenocarpus bacaba). DBH and stipe height differed significantly among species, however no differences were detected to total height. On the other hand, DBH, total and stipe heights differed among the forest types. Despite this result, biomass, basal area and density of the large palms were not explained by analyzed environmental variables. Otherwise, the carbon stock was distinct among forest types, being higher in the ombrophilous forest (7.00 Mg ha-1). The species differed from each other, being A. maripa the one with higher biomass and carbon stock (8.24 Mg ha-1; 4.12 Mg C ha-1) and E. precatoria the one with lowest (0,11 Mg ha-1; 0.055 Mg C ha-1). The carbon stock estimate was different between the model for palm and that one adopted for dicotyledonous trees. The study has concluded that density of individuals and species composition have distinct patterns among the analyzed forest types, and that these patterns refer indirectly to different carbon stocks by area unit. Nevertheless, the carbon stocks are not individually explained by tested variables, suggesting that other environmental determinants should be considered as limiting factors for the large palms carbon stocks among the different forest types of the studied ecotone.