Estimativas de produtividade de biomassa lenhosa ao longo de gradientes ambientais em florestas alagáveis na Amazônia Central

Abstract

The Amazon basin covers the largest world's tropical forest with an important role in the global carbon cycle due its ability to stock, absorb and emit carbon to the atmosphere. Wetlands occupy 30% of the Amazon basin and there are only few studies on the aboveground coarse wood biomass (AGWB) and its relation to environmental factors. This study estimated the carbon dynamics in the AGWB in black-water, clear-water and paleo- várzeas across edaphic and hydrological gradients. In most of the study areas three plots between 0,125 and 1 ha were established. Each hectare was divided into 16 subplots of 25 m x 25 m. All trees with diameter at breast height ≥ 10 cm (DAP = 1,30 m above the ground) were considered in the floristic inventory. In all areas the most abundant species were determined and five individuals of each species, with varying diameters, were selected to collect two wood samplesper tree to determine the wood density, annual diameter increment rates and trees age. A total of3.978 wood samples wer obtained at the DAP with an increment corer, 1,705 to examine wood density analysis and 2.273 to estimate annual diamtere increment rates. Wood density was determined by the ratio of the dry weight and fresh volume (g cm3). Samples were sanded for tree-ring analyses to identify the growth rings by macroscopical wood anatomical features. The mean diameter increment was determined by measuring the ring width and estimate the trees ages by ring counts. AGWB was estimated considers allometric models which consider DAP, specific wood density (ρ) and tree height of individuals as independent parameters. We analyzed the wood density of 372 species. Mean diameter incremente ranged from 2,1-3,0 mm and presented significant differences between the studied environments. The AGWB ranged from 55 to 353 Mg ha-1 in the black-water floodplain forest, 76-317 Mg ha-1 in the clear-water floodplains and 76-327 Mg ha-1 in the paleo-várzeas. Analyses at plot level indicated that wood density is mainly influenced by the flood. Soil fertility and terrestrial phase influence the diameter growth rates of tree species. No relationship between biomass stocks and hidroedafics factors were observed, however, AGWB productivity was significantly correlated with the flood duration. Carbon turnover in AGWB showed to be influenced by the clay content and flood duration. Flood duration was the main factor that influenced the dynamics of the analyzed typologies. Further studies in the Amazon basin are necessary to increase knowledge of the influence of hydrologic, soil and climatic variables in the flooded forests and how they will respond to environmental changes.