Crescimento em biomassa de árvores de dossel em florestas com lençol freático superficial no centro-sul da Amazônia

Abstract

As climate extremes intensify, there is evidence that they are leading to a decline in carbon absorption and storage in tropical forests. However, the factors driving growth variation in forests with shallow water tables (<5 m depth) remain largely unknown, and little is known about average growth behavior in these forests. The aim of this study was to determine how tree growth in aboveground biomass (inferred from growth rings) responds to variations in climatic and hydroedaphic conditions in the central-southern Amazon, where the landscape is dominated by forests with shallow water tables. We sampled 1012 canopy trees (at least 192 species, 36 families; DBH ≥ 30 cm) distributed across 54 1-ha plots along a 600 km transect to investigate how the interaction between local precipitation regime and water table depth influences average tree growth along the Purus-Madeira interfluve, both at the plot and individual levels. We also assessed whether wood density modulates tree growth under different hydroedaphic and climatic conditions. Data were analyzed using mixed-effects linear models. Our results reveal considerable variations in individual mean biomass increment, ranging from 5.89 to 103.15 kg/year, and in diameter growth, from 0.02 to 20.56 mm/year. The mean aboveground biomass increment at the plot level was 21.87 kg/year (± 3.8), while mean diameter growth was 3.02 mm/year (± 2.01). Remarkably, despite their lower soil fertility, forests located in the central part of the transect exhibited the highest aboveground biomass increments. Results at the plot level indicate higher biomass increments where more phosphorus is available. Conversely, higher total phosphorus levels in the soil decreased tree growth at both plot and individual levels, suggesting that this is controlled by water table fluctuation dynamics. We did not find an explicit interaction of water table depth with climate influencing tree growth. However, we did find a direct correlation between water table depth and biomass increments, suggesting sufficient soil water supply to support growth in drier and more demanding atmospheric conditions, but a constrained biomass growth where the water table maximum levels reach the surface. These findings support the hypothesis that local hydrology imposes significant constraints on the influence of forest climate effects, with potential implications for climate change feedbacks.