Simulações dos estoques de carbono em floresta tropical sazonalmente seca ante às mudanças climáticas

Abstract

The Caatinga is the largest and most continuous extension of Seasonally Dry Tropical Forests (SDTF) in the world. Climate changes designed for the Caatinga can have a significant impact on this ecorregion, influencing primary productivity, growth rate of remaining forests, dynamics and carbon (C) storage. However, there is little data available on stocks and C flows in these forest areas, due to the lack of structure to investigate at large spatial and temporal scales. Therefore, process based models were developed to study the dynamics of soil organic matter and make appropriate approaches to simulate the long-term biogeochemical cycle under different environmental conditions. From this perspective, the objectives of this study were: (1) to calibrate and validate the CENTURY model to simulate the stocks soil organic C (SOC) and C of biomass in areas of remaining caatinga, and (2) simulate the dynamics of SOC and C biomass stocks under different climatic scenarios projected until the year 2100. Twelve sites distributed in such a way that the annual rainfall gradient and soil types found in greater abundance under Caatinga were contemplated. The effect of climate projections for this century on C stocks was simulated by CENTURY using the climate scenarios established in the 5th Synthesis Report (AR5) by the Intergovernmental Panel on Climate Change (IPCC). The C stocks of the tree and shrub biomass simulated by the model were 25.5 and 23.4 Mg C ha-1 for calibration and validation, respectively. The values estimated by the model represent the pattern of herbaceous biomass (from 0.57 to 1.69 Mg C ha-1) and roots in caatinga forests. Regarding SOC stocks, the CENTURY presented an efficiency coefficient of 0.88 in calibration and 0.73 in validation. With an increase in aridity until the year 2100, the most frequent response would be the increase in the tree and shrub stratum (up to 3 Mg C ha-1) to the detriment of the herbaceous stratum (up to -0.6 Mg C ha-1) and an increase in the stock of SOC (up to 0.5 Mg C ha-1) in all climatic scenarios. The model suggests for some Caatinga conditions that greater structural investment in branches, large wood and coarse root may result in greater tolerance to extreme temperatures and water deficit. The CENTURY model adapted to the edaphoclimatic conditions of the Caatinga serves as a useful tool to estimate soil C stock, aboveground biomass and root of tree and shrub vegetation and herbaceous strata in remaining áreas.