Forests absorb atmospheric carbon dioxide (CO2) through photosynthesis and store carbon in vegetation and soils, making them important components of climate mitigation strategies. Fallen leaves, branches, and other organic material connect these stores as decomposition transfers carbon into soil or releases it to the atmosphere. However, this process varies with species composition, temperature, moisture, and topography.
In southern Brazil's mixed ombrophilous forests, characterized by the Brazilian pine, Araucaria angustifolia, research has largely emphasized vegetation and aboveground carbon. Less is known about how forest characteristics and terrain jointly shape carbon distribution across vegetation, litter, and soil, limiting understanding of the factors associated with carbon storage throughout these ecosystems.
A study (DOI: 10.48130/ebp-0026-0009) published in Environmental and Biogeochemical Processes on 13 July 2026 by Vinicius Costa Cysneiros's team, Federal University of Santa Catarina, reports that forest structure was positively associated with litter carbon, with slope moderating those relationships, while species evenness was positively associated with soil carbon.
The researchers surveyed nine permanent plots, each measuring 40 m by 50 m, within an 8.3-hectare forest fragment in Curitibanos, Santa Catarina. They measured and identified trees with trunk diameters of at least 10 cm, recording diameter and height. These measurements, combined with species-specific wood densities, supported estimates of aboveground biomass and carbon. The team also calculated stand basal area, the combined cross-sectional area of tree trunks, alongside indices describing species diversity and evenness.
To assess the forest floor, they collected litter from four quadrats per plot, dried and ground the material, and estimated its carbon content through laboratory analysis. Soil samples were collected from three successive layers down to 30 cm, with carbon concentrations and bulk density used to calculate stocks. Terrain data supplied slope estimates. Principal component analysis identified patterns among plots, and regression models tested relationships between forest characteristics and carbon stocks, including whether those relationships changed with slope. Average carbon stocks were 69.0 metric tons per hectare in aboveground vegetation, 3.7 in litter, and 73.0 in the sampled soil profile.
Soil held the largest share in most plots, although vegetation dominated in some. Greater basal area and aboveground carbon were significantly associated with higher litter carbon. Including slope in the models raised the proportion of litter carbon variation explained to approximately 79% and 76%, respectively. These positive relationships weakened as slopes increased and were not evident at the modeled high slope level. Species evenness, describing how equally individuals are distributed among species, explained approximately 57% of soil carbon variation in its regression model, without a significant slope interaction. Neither litter carbon nor the broader species diversity index significantly predicted soil carbon. Carbon stored specifically in Araucaria also failed to significantly predict litter carbon, despite the species' recognized importance in this forest type and its contribution to aboveground carbon storage.
"Together, the results suggest that forest carbon accounting benefits from considering ecosystem compartments and local environmental differences. Protecting forest structure and maintaining balanced tree communities may support carbon storage, but management applications require further testing." - Vinicius Costa Cysneiros, Federal University of Santa Catarina
The authors call for broader sampling, deeper soil measurements, and long-term monitoring across soil, climate, and topographic gradients to establish how widely these relationships apply.