The effects of forest thinning on soil carbon stocks and dynamics: A meta-analysis

Forest thinning is widely used in forest management activities and has complex effects on underground carbon processes. Although many case studies have been done, how forest thinning affects soil carbon stocks and dynamics remains unclear, especially at different recovery stage. Here, we synthesized the results from 53 peer reviewed publications and conducted a meta-analysis to evaluate the general responses of 10 variables related to forest soil carbon stocks and dynamics to forest thinning management. Overall, we did not find remarkable effects of thinning on soil moisture, fine root biomass and soil carbon stocks (including soil total carbon, soil organic carbon and microbial biomass carbon). However, thinning resulted in a significant reduction in litterfall production (-23.7%), while significantly increasing soil temperature (+8.7%) and soil respiration (+29.4%) in general. In particular, the effect of forest thinning on soil respiration was significant in light (thinning intensity < 33%) to moderate (33-67% of thinning intensity) thinning. In the early stage of recovery (<= 2 yr after thinning), this effect was also significant. Thinning significantly increased soil respiration in both broadleaved (+35.6%) and mixed forests (+9.3%) but not in coniferous forest due to the difference of litterfall quality. These results provide a synthetic review of the effects of forest thinning on soil carbon stocks and dynamics and may help to improve forest management strategies.