MODELING SOIL CARBON STOCKS IN BRAZILIAN NATIVE FORESTS AND EUCALYPTUS PLANTATIONS

Assessing soil carbon (C, t ha⁻¹) stocks is crucial for developing strategies to enhance C sequestration and mitigate climate change. However, soil sampling and analysis are costly, particularly in extensive forested areas. This study evaluates models for estimating soil C stocks in tropical environments. Composite soil samples were collected from Eucalyptus plantations and native forests in the Brazilian Atlantic Forest, Cerrado, and Amazon biomes at depths of 0-15, 15-30, 30-50, and 50-100 cm. The dataset encompass diverse soil textures and climatic conditions, totaling 156 sampling points across four depths, resulting in 624 samples in the three biomes. Total organic C was quantified via dry combustion, and bulk density determined using the volumetric ring method for C stock calculations. Soil particle size distribution was analyzed to support modeling purposes. Public databases containing 19 environmental parameters, including atmospheric temperature, precipitation, elevation, and slope, were incorporated. Machine learning and multivariate models were tested for current soil C stock estimations. Preliminary multiple linear regression analysis showed an R² of 0.72 for estimating soil C stocks in Eucalyptus plantations within the 0-30 cm soil layer. Key predictors included soil clay content, precipitation, elevation, and slope. C stocks increased with clay content, likely due to enhanced organo-mineral stabilization of organic matter. Water limitations reduced C stocks, presumably due to lower biomass inputs than higher precipitation areas. In the Atlantic Forest, C stocks averaged 34 t ha⁻¹ in Bahia and Espírito Santo states, and 56 t ha⁻¹ in São Paulo. Quantifying C stocks in tropical Eucalyptus plantations and native forests supports governments and private forestry initiatives in C inventory reporting, and climate mitigation strategies. Enhancing soil C in forests, which would ultimately result in improved soil quality and health, is a step toward achieving the sustainable development goals of “Climate Action” (SDG13) and “Life on Land” (SDG15) of the United Nations’ 2030 agenda.