Forests are often described as natural climate allies because trees remove carbon dioxide from the atmosphere and store carbon in their trunks, branches, roots, fallen leaves, and surrounding soil. Yet carbon is not distributed evenly across these compartments, and the factors controlling where it accumulates remain poorly understood in many threatened forest ecosystems.
A new study of a mixed ombrophilous forest fragment in southern Brazil shows that forest structure, tree species evenness, and terrain slope jointly influence how carbon is divided among living vegetation, forest litter, and soil.
"Carbon storage cannot be fully understood by measuring trees alone. Our results show that vegetation, litter, soil, biodiversity, and topography must be considered together to reveal how a forest functions as a carbon sink," said corresponding author Vinicius Costa Cysneiros of the Federal University of Santa Catarina.
The research focused on an 8.3 hectare forest fragment in Curitibanos, Santa Catarina. This forest type, also known as Araucaria forest, is part of the Brazilian Atlantic Forest and is characterized by the presence of the iconic Brazilian pine, Araucaria angustifolia. The region has a humid temperate climate, cold winters, frequent frost, and a landscape increasingly surrounded by pasture, agriculture, and commercial forestry.
Researchers surveyed nine permanent plots, recording tree diameter, height, species composition, and forest structure. They estimated carbon stored in aboveground vegetation, collected litter from the forest floor, and measured soil carbon at depths of up to 30 centimeters.
Carbon storage varied substantially among the plots. Soil contained the largest share of total carbon in most locations, although vegetation stored more carbon than soil in several plots. Average aboveground forest carbon was approximately 69 metric tons per hectare, while total soil carbon averaged about 73 metric tons per hectare. Litter contained a much smaller but ecologically important carbon stock.
Plots with a greater basal area, meaning more tree trunk area per unit of land, and higher aboveground carbon stocks generally contained more carbon in the litter layer. Larger and denser forests produce more leaves, branches, reproductive materials, and other organic residues that eventually reach the forest floor.
However, the positive relationship between forest biomass and litter carbon became weaker on steeper slopes. Organic material can accumulate more easily on relatively flat ground, while rainfall, runoff, and gravity may move litter away from inclined areas.
Tree diversity also influenced belowground carbon storage. The researchers found that greater species evenness was associated with higher soil carbon stocks. Species evenness describes how equally individual trees are distributed among the species present. A forest dominated by only a few species has lower evenness than one in which species occur in more balanced proportions.
The study did not detect a direct relationship between litter carbon and soil carbon. The researchers suggest that seasonal timing may partly explain this result. Field sampling occurred during winter, when colder temperatures can slow litter decomposition and delay the transfer of carbon from fallen plant material into soil. Soil carbon also reflects organic matter accumulated over much longer periods, while the litter layer changes relatively quickly.
The authors caution that the study involved a limited number of plots and shallow, stony soils that prevented sampling at greater depths. Additional research across seasons and broader climatic, soil, and topographic conditions will be needed.
Nevertheless, the findings emphasize that forest based climate strategies should assess carbon throughout the ecosystem rather than focusing only on standing trees. Protecting tree diversity, supporting forest regeneration, and accounting for local terrain may improve estimates of carbon storage and guide more effective conservation and climate mitigation programs.
===
Journal reference: Theodoroski GN, Cysneiros VC, Schmitt DE, Topanotti LR. 2026. Carbon partitioning in a mixed ombrophilous forest fragment in southern Brazil. Environmental and Biogeochemical Processes 2: e013 doi: 10.48130/ebp-0026-0009
https://www.maxapress.com/article/doi/10.48130/ebp-0026-0009
===
About the Journal:
Environmental and Biogeochemical Processes (e-ISSN 3070-1708) is a multidisciplinary platform for communicating advances in fundamental and applied research on the interactions and processes involving the cycling of elements and compounds between the biological, geological, and chemical components of the environment.
