A forest biodiversity experiment (FAB) focused on trees of our region investigates the consequences of multiple dimensions of tree diversity for soil, food webs, plant communities and ecosystems. FAB is designed to unravel effects of three forms of biological diversity: species richness (SR), functional diversity (FD), and phylogenetic diversity (PD). We define FD as the representation of multiple traits of leaves, roots, seeds, and the whole organism that are correlated with species positions along gradients of resource supply, growth, and decomposition. PD is the representation of evolutionary lineages measured as the genetic distances between species. While PD and FD are often correlated, convergent evolution and adaptive differentiation can decouple them. When functional traits that drive specific ecosystem functions are not phylogenetically conserved, PD and FD may give contrasting predictions. SR, PD, and FD are not independent, and we posit that PD may help explain SR effects, and FD may help explain both PD and SR effects. Thus FAB is designed to examine the separate and combined effects of all three components of diversity for multiple ecosystem functions and to distinguish between ???sampling??? and ???complementarity??? effects of biodiversity. Due to the long lag between planting tree seedlings and determining effects of tree composition and diversity on ecosystem functioning, fewer experiments have been established to elucidate the role of biodiversity in the functioning of forest ecosystems than grassland experiments. FAB will contribute to this gap and is becoming a member of the IDENT and TreeDiv network of forest biodiversity experiments (www.treedivnet.ugent.be). Hypotheses: 1. PD, FD, and SR will all contribute to increased productivity, stability, and diversity of other trophic levels (herbivores, predators, parasitoids, soil microbes, soil flora and fauna) as well as to greater soil C sequestration. 2. Because PD incorporates both the number of species and measurement of their evolutionary divergence, PD will explain more of the variation in ecosystem productivity and stability than SR. Similarly, among-species FD will explain more variation in these ecosystem functions than SR or PD. 3. Plant assemblages of similar SR but comprised of increasingly divergent PD or FD will show increasing divergence in ecosystem functions. 4. Species with functional traits not yet present in a plot will more easily invade than species with traits similar to the established species. The FAB single species plots will allow us to test hypotheses about the importance of plant functional traits in influencing ecosystem properties (e.g., NPP, soil C, N mineralization) and plant-associated microbial communities. For example, we expect that plant species that increase concentrations of polyvalent soil cations (e.g., because of unique base cation chemistry or because of effects on soil acidity that influence Al and Fe solubility) will promote soil C stabilization through mineral-organic matter interactions and the formation of microaggregates that protect soil C from decomposition.