Effects of forest thinning on soil microbial biomass and enzyme activity

Forest thinning is a management measure intended to promote forest regeneration and improve soil microbial activity. However, a comprehensive evaluation of the effects of forest thinning on soil microbial biomass and enzyme activity is yet to be conducted. Therefore, this study analyzed 1059 data points from 69 studies at the global scale to investigate the effects of forest type, thinning intensity, recovery time, and mean annual precipitation and temperature on microbial biomass and enzyme activity. Thinning significantly increased the microbial biomass carbon (8.92 %), nitrogen (17.40 %), and phosphorus (29.98 %) levels and saccharase (9.21 %) and urease (10.08 %) activities. The response ratio of soil microbial biomass was higher in coniferous forests than that in broadleaf or mixed forests, and the response ratio of saccharase activity was higher in mixed forests than in coniferous or broadleaf forests. The response ratios of microbial biomass and phosphatase activity were higher in the late recovery time than those in the early and medium recovery times. Soil microbial biomass and enzyme activity first increased and then decreased with thinning intensity but decreased with mean annual precipitation and temperature. In conclusion, this study highlights that thinning significantly increases soil microbial biomass and enzyme activity, and a moderate thinning intensity (33.3-66.6 %) and long-term recovery (>10 years) are highly conducive to improving soil microbial activity. These results provide a basis for forest ecosystem management and the formulation of scientific and reasonable thinning parameters.