Litter and soil biogeochemical parameters as indicators of sustainable logging in Central Amazonia

Abstract One-fourth of Brazilian Amazonia is managed for timber production, but only a few logging sites follow sustainable forest management plans (SFMPs). Amazon forests without SFMPs are susceptible to deforestation because such plans integrate the use of forest products and conservation goals by allowing selective wood extraction following regulations. It remains uncertain whether reduced-impact selective logging (17–20 m3 ha−1 yr−1 of 38–70 species), typical of SFMPs, changes forest regeneration, carbon (C) stocks, and nutrient cycling. Here, we tested the hypothesis that litter and soil biogeochemical parameters serve as indicators of sustainable logging as forest regeneration, C stocks, and C-to-nutrient ratios in soil and litter become similar to those in primary forests as time elapses after logging. We used a chronosequence spanning nine years since logging to relate litter and soil (0–10, 10–30, 30–50 cm) C stocks and 12 and 15 biogeochemical parameters, respectively, canopy cover and tree seedling density (10–150 cm tall) in sustainably managed upland evergreen Amazon forests. In one unlogged and four logged stands sampled three, five, seven, and nine years after logging, we compared 15 permanent plots (three replicated 0.5 ha plots per time-since-logging category). Five biogeochemical parameters explained >80% of the variation in soil and litter among logged and unlogged stands. Litter parameters were more sensitive to logging than soil parameters, where litter C stocks and C-to-nutrient ratios increased systematically after logging. Canopy cover decreased over time and was ~14% lower nine years after logging. Total seedling density did not change consistently over time but was ~54% higher seven years after logging. Our data suggest that the SFMP guidelines have served the purpose of maintaining soil quality and forest regeneration. Litter and soil parameters can be useful indicators of sustainable forest management in upland evergreen forests in Central Amazonia.