A novel comparative research platform designed to determine the functional significance of tree species diversity in European forests

One of the current advances in functional biodiversity research is the move away from short-lived testsystems towards the exploration of diversity-ecosystem functioning relationships in structurally morecomplex ecosystems. In forests, assumptions about the functional significance of tree species diversityhave only recently produced a new generation of research on ecosystem processes and services. Novelexperimental designs have now replaced traditional forestry trials, but these comparatively young exper-imental plots suffer from specific difficulties that are mainly related to the tree size and longevity. Treespecies diversity experiments therefore need to be complemented with comparative observational stud-ies in existing forests. Here we present the design and implementation of a new network of forest plotsalong tree species diversity gradients in six major European forest types: the FunDivEUROPE ExploratoryPlatform. Based on a review of the deficiencies of existing observational approaches and of unresolvedresearch questions and hypotheses, we discuss the fundamental criteria that shaped the design of ourplatform. Key features include the extent of the species diversity gradient with mixtures up to five species,strict avoidance of a dilution gradient, special attention to community evenness and minimal covariationwith other environmental factors. The new European research platform permits the most comprehen-sive assessment of tree species diversity effects on forest ecosystem functioning to date since it offers acommon set of research plots to groups of researchers from very different disciplines and uses the samemethodological approach in contrasting forest types along an extensive environmental gradient