Diversity and identity of economics traits determine the extent of tree mixture effects on ecosystem productivity

Abstract

Abstract Although both observational and experimental studies have shown that positive tree species diversity–productivity relationships are predominant in global forests, weak or the lack of tree species diversity and productivity relationships also exist. Growing evidence has revealed that ecosystem productivity depends more on the functional characteristics of species than on their number. However, exactly to what extent tree diversity effects on ecosystem productivity are influenced by the variability and composition of functional traits have rarely been tested both across and at given species richness (SR) levels. Here, we employed a meta‐analysis of global‐scale data from 59 tree diversity experiments to examine how the diversity and community‐weighted means (CWMs) of economics traits determine the outcomes of tree mixture effects on productivity across and within SR levels. We found that the positive effects of tree mixtures on productivity were strengthened by the increasing multidimensional functional dispersion (FDis) and the CWM of leaf nitrogen content both across and within two‐ and four‐species mixtures. Moreover, the multidimensional FDis and the CWM of leaf nitrogen content increased the complementarity effect rather than the selection effect. Synthesis. Our findings suggest that both diversity in the leaf economics spectrum and trait concentration on the ‘fast’ end of the spectrum strengthen biodiversity–ecosystem functioning relationships. This study provides mechanistic insights into the potent roles of plant economics traits, especially leaf nitrogen content, in determining the magnitude (and even directionality) of the biodiversity–ecosystem functioning relationships in forest ecosystems.