Abstract
One-fourth of Brazilian Amazonia is managed for timber production, but only a small portion of active 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 aimed at reducing the long-term impact of logging. However, it remains uncertain whether reduced-impact selective logging typical of SFMPs (17–20 m3 ha−1 yr−1 of 38–70 species) 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 progressively similar to those of primary forests as time elapses after logging. We used a chronosequence spanning nine years since logging to relate litter and soil (at 0–10, 10–30, 30–50 cm depth) C stocks and 12 and 15 biogeochemical parameters, respectively, as well as canopy cover and tree seedling density (10–150 cm tall) in 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). We found that five parameters explained >80% of the variation in soil and litter properties among logged and unlogged stands. Litter parameters were more sensitive to logging than soil parameters, as 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.
Highlights
Tropical forests play a crucial role in regulating Earth's climate (Le Quéré et al, 2015), but only a few forests in the tropics follow certified sustainable forest management plans-SFMPs (FAO, 2010; Kraxner et al, 2017)
We tested the hypothesis that litter and soil biogeochemical parameters serve as indicators of sustainable logging
We focused on the following questions: (i) Do seedling density and canopy cover vary with time since logging? (ii) Do litter and soil C stocks change with time since logging? (iii) Which litter and soil biogeochemical parameters (e.g., C, nitrogen-N, phosphorus, calcium, magnesium) best explain differences in litter and soil between forest stands over time? We hypothesized that: (H1) seedling density will be higher in recently logged forests and will negatively correlate with canopy cover; (H2) soil and litter C stock, and (H3) litter C-to-nutrient ratios (e.g., C:N) will be higher in recently logged forests, decreasing with time since logging
Summary
Tropical forests play a crucial role in regulating Earth's climate (Le Quéré et al, 2015), but only a few forests in the tropics follow certified sustainable forest management plans-SFMPs (FAO, 2010; Kraxner et al, 2017). Typical SFMP guidelines integrate the use of timber—and non-timber—forest products while maintaining healthy forests (Burivalova et al, 2017; Canova and Hickey, 2012; Putz et al, 2012; Sasaki et al, 2012), conservation goals, and social justice (de Toledo et al, 2017) by allowing wood extraction following existing regulations. Managed counterparts (MacDicken et al, 2015) For this reason, expanding and improving SFMPs (Piponiot et al, 2019) is necessary to achieving local sustainability while simultaneously contributing to regional and global conservation and climate change mitigation goals (e.g., REDD+; Laurance et al, 2014; Sist and Ferreira, 2007). Typical SFMPs include reduced-impact selective logging operations to harvest a selective number of marketable tree species possessing high wood value from primary forests (17–20 m3 ha−1 yr−1 of 38–70 species; Dykstra et al, 2001). Given future harvest cycles rely on the natural regrowth of Amazon forests (Pinho et al, 2009) that support 190 to 300 tree species ha−1
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