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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 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.
								

The experimental site was burned, then mulched with wood chips (from non-native western red cedar [Thuja plicata]) to prevent regrowth of herbaceous species. The experiment was planted over one week in late May 2013 with regionally sourced bare root seed-lings of unknown genetic relatedness that ranged from 1 to 2 years in age. Prior to planting, seedling roots were coated with commercial ectomycorrhizal and endomycorrhizal inoculum including species known to associate with all genera included in the experiment (Bio Organics, New Hope, PA). We used sprinkler irrigation to water newly planted seedlings ad libitum through June and July 2013. We replanted seedlings as needed in May/June 2014 to 2015; mortality was roughly 7 to 10 percent following replanting.
								

The FAB 1 High density diversity experiment consists of 8,960 trees of 12 native species. Four of these species are gymnosperms: eastern red cedar (Juniperus virginiana) and white (Pinus strobus), red (P. resinosa), and jack (P. banksiana) pine. The eight angiosperm species include red (Quercus rubra), pin (Q. ellipsoidalis), white (Q. alba), and bur (Q. macrocarpa) oak; red maple (Acer rubrum) and box elder (A. negundo); paper birch (Betula papyrifera); and basswood (Tilia americana).

Each of FAB`s three blocks(spaced 4.5 m apart) consists of either 46 or 47 square plots, each 3.5 m on the edge; plots are planted with one, two, five, or 12 species, with two-species plots additionally designed to tease apart functional and phylogenetic diversity. Each plot contains 64 trees, planted at 0.5 m intervals. Within a block, all trees are planted on a contiguous grid, without extra space in between plots. 

Each block contains 12 monocultural plots and 28 bicultural (two-species) plots; each of these plot types (or compositions) is therefore replicated three times across the experiment. Each block also contains either three or four random-draw five-species poly-cultures, the compositions of which are not replicated in the experiment, giving replication of the five-species level of richness but not of each five-species polyculture's composition. Each block also contains three or four 12-species polycultures, such that this composition is replicated 10 times across the experiment. Half of the 28 bicultural plot compositions were chosen by random draw. The other remaining bicultures were chosen using a stratified random approach designed to provide plots both low and high in PD and FD.
								

Carbon fraction analysis was carried out to separate soluble cell contents, hemicellulose and bound proteins, cellulose, and acid unhydrolyzable residues (including lignin and hereafter referred to as AUR) of dried, ground leaves. All mass and carbon fraction data are reported here without having ash factored out and ash weight (or recalcitrant weight) is presented as a percent of total mass at collection. Thus, ash-free weight can be calculated, as in the accompanying manuscript.		

Three bags were not recovered, giving a final sample size of 597 bags across 150 strings. Carbon fraction data is also incomplete for some bags due to loss of ground litter during analysis.
								

Litterbags were constructed with either 1 species of litter or mixtures of 2, 5, or 12 species. In October 2014, we collected freshly senesced litter from 12 species of adult trees of native provenance on private property in Hudson, WI, USA (Juniperus virginiana; eastern red cedar) and at Cedar Creek Ecosystem Science Reserve (CCESR; all other species). Litter was air dried and stored at room temperature in darkness. In spring 2015, litter was used to fill 20 cm by 20 cm square bags constructed of 1 mm fiberglass mesh. Bags were filled with 2.5 g of air-dried litter and heat-sealed. All weights were adjusted to reflect oven-dried (> 24 hours at 60 degrees Celsius) weight and loss-on-handling as estimated from one-species litterbags that had been assembled, deployed in the field, and immediately returned and weighed. 					
	
All litterbags were deployed in a common ``garden`` at CCESR on 12 June, 2015. The common garden was located in a secondary, unmanaged stand of trees, consisting primarily of Populus grandidentata (bigtooth aspen) and Pinus strobus (white pine) interspersed with Acer spp. (maples). Understory growth was minimal and largely consisted of the seasonally abundant legume Amphicarpaea bracteata (hog peanut). A duff layer of roughly 0.25 cm in depth covered the mineral soil horizon in the common garden and was left intact. Four replicate litterbags with the same composition were tied together to form 150 strings. Each string of four litterbags was stretched to its full length so that bags were not touching and staked in place so that the entire bottom surface of each bag was in contact with the existing litter layer. Bags were not covered when deployed but became covered with a layer of freshly fallen litter from four months post-deployment onward. Because bags were deployed over an area large enough to vary in microtopography, overstory vegetation, exposure to deer trampling, etc., we divided strings  into three blocks, with 50 strings arranged randomly within each garden block. Strings were assigned to blocks so that each bag composition was represented across all three blocks.
					
One litterbag from each of the 150 strings was collected at 62 days (two months), 124 days (four months), 363 days (one year), and 731 days (two years) following deployment. On collection, each bag was cleaned manually of mineral soil, allochthonous litter, ingrown plant material, and soil animals (including small earthworms). Litter was removed from each bag, cleaned further, oven dried at 60 degrees for > 24 hours, and weighed. Dried litter was then ground in a Wiley mill and carbon fractions were quantified as described in lab analysis. Post-decomposition litter was ashed at 550 degrees Celsius for four hours.
								

We used an ANKOM 200 fiber analyzer (Macedon, NY, USA) to measure the concentration by mass of four operational `carbon fractions` in ground litter.