Disentangling biodiversity and climatic determinants of wood production.

Background - Despite empirical support for an increase in ecosystem productivity with species diversity in synthetic systems, there is ample evidence that this relationship is dependent on environmental characteristics, especially in structurally more complex natural systems. Empirical support for this relationship in forests is urgently needed, as these ecosystems play an important role in carbon sequestration. Methodology/Principal Findings - We tested whether tree wood productionis positively related to tree species richnesswhile controlling for climatic factors, by analyzing 55265 forest inventoryplots in 11 forest types across five European countries. On average, wood productionwas 24% higher in mixed than in monospecificforests. Taken alone, wood productionwas enhanced with increasing tree species richnessin almost all forest types. In some forests, wood productionwas also greater with increasing numbers of tree types. Structural Equation Modeling indicated that the increase in wood productionwith tree species richnesswas largely mediated by a positive association between stand basal areaand tree species richness. Mean annual temperature and mean annual precipitation affected wood productionand species richnessdirectly. However, the direction and magnitude of the influence of climatic variables on wood productionand species richnesswas not consistent, and vary dependent on forest type. Conclusions - Our analysis is the first to find a local scale positive relationship between tree species richnessand tree wood productionoccurring across a continent. Our results strongly support incorporating the role of biodiversity in management and policy plans for forest carbon sequestration.