Despite considerable research demonstrating that biodiversity increases productivity in forests and regulates herbivory and pathogen damage, there remain gaps in our understanding of the shape, magnitude, and generality of these biodiversity-ecosystem functioning (BEF) relationships. Here, we review findings from TreeDivNet, a global network of 25 tree diversity experiments, on relationships between levels of biodiversity and (a) tree growth and survival and (b) damage to trees from pests and pathogens. Tree diversity often improved the survival and above- and belowground growth of young trees. The mechanistic bases of the diversity effects on tree growth and survival include both selection effects (i.e., an increasing impact of particular species in more species-rich communities) and complementary effects (e.g. related to resource differentiation and facilitation). Plant traits and abiotic stressors may mediate these relationships. Studies of the responses of invertebrate and vertebrate herbivory and pathogen damage have demonstrated that trees in more diverse experimental plots may experience more, less, or similar damage compared to conspecific trees in less diverse plots. Documented mechanisms producing these patterns include changes in concentration, frequency, and apparency of hosts; herbivore and pathogen diet breadth; the spatial scale of interactions; and herbivore and pathogen regulation by natural enemies. Our review of findings from TreeDivNet indicates that tree diversity experiments are extending BEF research across systems and scales, complementing previous BEF work in grasslands by providing opportunities to use remote sensing and spectral approaches to study BEF dynamics, integrate belowground and aboveground approaches, and trace the consequences of tree physiology for ecosystem functioning. This extension of BEF research into tree-dominated systems is improving ecologists’ capacity to understand the mechanistic bases behind BEF relationships. Tree diversity experiments also present opportunities for novel research. Since experimental tree diversity plantations enable measurements at tree, neighbourhood and plot level, they allow for explicit consideration of temporal and spatial scales in BEF dynamics. Presently, most TreeDivNet experiments have run for less than ten years. Given the longevity of trees, exciting results on BEF relationships are expected in the future.
Bibliographical noteFunding Information:
JJG, JCB, and PBR were supported by grants from the US National Science Foundation Long-Term Ecological Research Program (LTER) including DEB-0620652 and DEB-1234162 ; further support was provided by the Cedar Creek Ecosystem Science Reserve and the University of Minnesota . NE, OF, AS and HB acknowledge funding by the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, funded by the German Research Foundation ( FZT 118 ). HB, AS, MS and MSL appreciate the funding of BEF-China by the German Research Foundation ( DFG FOR 891/1-3 ). JP acknowledges funding from the Smithsonian Institution and a generous donation from John Ryan. MW was supported by the fund of the Swedish Energy Agency (project no. 36654-2). HK and DCZ acknowledge funding from the German Research Foundation ( DFG CRC 990-EFFORTS ). CN acknowledges funding from the German Research Foundation ( DFG Project NO 1225/2-1 ). QP acknowledges support from the Walloon Public Service – Department of Nature and Forests (SPW-DNF) , through the project ‘Accord-cadre de recherche et de vulgarisation forestières’. MV was funded as postdoctoral fellow of FWO-Vlaanderen. CM, AP and DG acknowledge funding from the Natural Sciences and Engineering Research Council of Canada . MSL, JB, HB, BC, HJ, AH, BM, QP (Associated Partner), and KV received funding within the FunDivEUROPE project from the European Union Seventh Framework Programme (FP7/2007–2013) under grant agreement n∘ 265171 . Appendix A
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- Biodiversity experiment
- Plantation forest
- Research infrastructure