Scale-dependent effects of tree species diversity on soil erosion resistance

Globally, vegetation establishment is an important approach for controlling soil erosion, which induces land degradation. However, the understanding of the effects of tree species diversity on soil erodibility across spatial scales remains incomplete. This study employed the Universal Soil Loss Equation model to quantify soil erodibility and aligned it with tree species diversity data obtained from the Global Forest Biodiversity Initiative database. Our findings revealed a global decrease in soil erodibility with increases in tree species diversity, though this relationship varies among biomes and ecoregions. Specifically, soil erodibility decreased with increasing tree species diversity in 6 of the 11 biomes and 54.90% of the ecoregions analyzed. Comprehensive analyses revealed that increased productivity, NDVI, and basal area mediated this reduction in erodibility across both groups. In ecoregions where tree species diversity was negatively correlated with soil erodibility, lower precipitation during the driest month and quarter, higher precipitation seasonality, lower silt content, and higher elevation were observed compared with those of the ecoregions with positive correlations between tree species diversity and soil erodibility. Among ecoregions characterized by clay content > 18.3% and silt content < 40%, 79.55% exhibited a reduction in soil erodibility as tree species diversity increased. These findings highlight the inherent spatial variability and mechanistic complexity of biodiversity-soil erodibility relationships, underscoring the need for targeted, soil-specific restoration strategies.