Forest thinning increases soil carbon stocks in China

Thinning is a common forest management practice. However, its impact on soil organic carbon (SOC) stocks is still unknown. Therefore, we conducted a meta-analysis of 270 measurements from 77 articles to evaluate the effect of forest thinning on SOC stocks in mineral soil (0–30 cm) across planted forests in China. The results showed that, compared to reference (non-thinned) plantations, thinning significantly increased SOC stocks in planted forests by 7.2%. Among different thinning intensities, moderate thinning (35–55% of thinning intensity) increased SOC stocks in planted forests (+16.1%) more than other levels of thinning intensity. However, the positive effect of thinning on SOC stock was significant > 5 years after harvesting. In the humidity-restricted areas (humidity index (HI) < 30), the increase in SOC stocks after thinning was significantly higher than that of other areas. In addition, thinning increased the sensitivity (i.e. slope value) of soil total nitrogen (TN) stocks changes to SOC stocks. Therefore, we conclude that forest thinning strategy is potentially a viable silvicultural measure to increase SOC fixation in planted forests. Our results provide a reference for the formulation and implementation of future forest management strategies.