Anthropogenic disturbance mediates soil water effect on diversity-productivity relationships in a temperate forest region

Mixed-species forests are known to provide enhanced ecosystem functioning when compared with monocultures. The strength of the positive diversity effect is, however, largely dependent on environmental conditions and the human footprint. The specific patterns of context-dependence effects of diversity on productivity and their causal relationships are not well known, especially regarding large-scale natural plant communities. Accordingly, the focus of this study is to evaluate effects of environmental variables on biodiversity-productivity relationships (BPR) in the temperate forest region of North-Eastern China. We used a structural equation modeling and hierarchical Bayesian model to assess individual and interactive effects of human disturbance, environmental factors, and species diversity on productivity. The SEMs showed that the negative interaction effect of human disturbance and mean annual temperature on species diversity was greater than that of human disturbance on species diversity. The positive diversity effects on forest production were severely reduced under stressful soil water conditions due to increased competition for soil water resources. The positive diversity effects were greater under harsh annual mean temperature conditions. The biodiversity effects on productivity were influenced by negative interactive effect of the human footprint and soil water availability. Our results suggest that current management strategies for diversity conservation may be countered by robust negative interactive effects and thus, may be inefficient in temperate forest regions. The variations in the strength of the relationships between tree species diversity and forest productivity are critically dependent on several environmental stressors. Our results highlight the important role of human disturbance in mediating the response of BPR to soil water deficit, and the crucial role of management strategy to prepare for future climatic challenges in our temperate forest region.