How does forest restoration affect the recovery of soil quality? A global meta-analysis for tropical and temperate regions

Restoring forest ecosystems to reverse soil degradation is critical to maintain environmental quality, forest and agricultural productivity, biodiversity conservation, and to provide valuable ecosystem services. Yet the impacts of forest restoration on soil quality remain under-investigated. Here we aim to address a key knowledge gap: how does forest ecosystem restoration affect the recovery of soil quality in tropical and temperate regions? We conducted a global meta-analysis to compare soil physical, chemical, and biological properties between restoring forests and reference old-growth/less-disturbed forests. We revealed for the first time that differences between restoring and reference forests are lower for physical (12-25%; based on median values of effect size) and chemical (10-74%) properties than for biological (32-90%) properties. More specifically, bulk density (12% of difference), pH (10%), and enzyme activity (32%) had mean values in restoring forests closer to those observed in reference forests. Overall, our results suggest that the restoration of soil properties was greater in tropical regions, after longer periods (>30 years), through passive restoration, and over pasturelands. Our global meta-analysis helps to fill the soil information gap in forest restoration and increase our understanding of how to improve soil quality through forest restoration and soil monitoring processes in tropical and temperate regions.