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Carbon plays a key role in determining soil health, which is defined as the soil's capacity to maintain environmental functions and biological productivity. In this study, C cycling was evaluated in soils along a gradient of land use, from native forest (NF), reforested sites (secondary forest – SF, Araucaria angustifolia – AR, Pinus elliottii – PI), clear-cut P. elliottii stands (CT) to farmland (AG). NF, AR, and SF sites had lower litter C:N ratios than PI, CT, and AG sites. Soils under forests had more organic C than CT and AG soils, whereas soils with native species had more microbial biomass C than PI, CT and AG soils. Both metabolic quotient (qCO₂) and dehydrogenase activity increased with land use. Multivariate analysis revealed that soils of AR and SF were similar to NF and differed from CT and AG, which had higher qCO₂ and dehydrogenase activity, suggesting microbial stress. Litter C:N ratios and soil microbial biomass C, moisture, CO₂ evolution, and cellulase activity discriminated most effectively between land uses. Reforestation with native species restored soil properties to levels similar to those in NF, being more sustainable, whereas reforestation with the exotic P. elliottii made soils more similar to AG soils.
