Drivers of soil organic carbon recovery under forest restoration: a global meta-analysis

Abstract Forest restoration by planting tree seedlings is a crucial strategy to mitigate climate change and restore forest functions. The Intergovernmental Panel on Climate Change (IPCC) targets to remove around 70 Pg carbon (C) from the atmosphere via forest restoration. However, the impact of forest restoration on the recovery of soil organic carbon (SOC) and its driving factors remains unclear. Here, we conducted a global meta-analysis, based on 348 observations from 144 studies across 150 sites, to evaluate the recovery time of SOC and the driving factors of surface SOC recovery during forest restoration. We found that soil clay content and stand age were recognized as the dominant factors regulating SOC recovery during forest restoration. Overall, SOC recovery was lower in boreal and Mediterranean forests than that in tropical, subtropical, and temperate forests, lower in burned areas and mine sites than that in other sites, and lower in soils with 0%–20% clay contents than that in those with higher clay contents, and comparable among soils with different pH values. Across studies, surface SOC in restored forests with stand ages ranging from 1 to 200 years did not fully recover to the levels of reference forests. However, the SOC recovery rate was roughly twice as fast in tree polycultures (~ 10 years to plateau) as that in monocultures (~ 20 years). This global synthesis identifies critical drivers of SOC recovery during forest restoration and provides important insights into SOC management in forests. Graphical Abstract