The Site
Experimental Design
We established a gradient in tree species richness comprising monocultures, two- and four-species mixtures. In addition, we set up a mycorrhizal type treatment with three levels comprising only trees with arbuscular mycorrhizal fungi (AMF), only trees with ectomycorrhizal fungi (EMF), and AMF- and EMF-trees in mixture (Ferlian et al., 2018).
For species selection, a pool of all potentially relevant tree species was assembled using the following criteria: (1) deciduous angiosperm that is native to Germany; (2) adapted to site conditions; (3) species are widely spread across the angiosperm phylogeny; and (4) economical or recreational relevance in Germany. The tree species that met these criteria were separated into two groups, AMF and EMF. We selected five species from each pool that contributed to minimising trait differences other than mycorrhizal type between AMF and EMF species pools which may confound effects of mycorrhizal type on ecosystem functions.
We planted replicated monocultures of each species (10 x 2 plots), a comprehensive set of possible two-species combinations (30 plots), and five replicates of different species compositions in the four-species mixtures (30 plots). In total, 80 plots were established in two blocks. Within each block, spatial arrangement of plots is random. The plots have a size of 121 m2 (11 x 11 m) with a 1.5 m buffer consisting of the outermost tree rows and a core area of 8 x 8 m. Samples and measurements are exclusively taken in the core area to reduce edge effects. Trees were planted in a distance of 1 m in a regular pattern. 140 tree individuals per plot were planted, which adds up to 11,200 trees in total.
Between- and within plot spatial design (modified after Ferlian et al., 2018; aerial photograph: ©2017 Google,
Map data ©2017 GeoBasis-DE/BKG (©2009))
Location
The MyDiv Experiment is located in Saxony-Anhalt, Germany, southwest of Halle (51° 23‘ N, 11° 53‘ E) at the Bad Lauchstädt Experimental Research Station of the Helmholtz Centre for Environmental Research – UFZ (Ferlian et al., 2018). The site is located at 114 – 116 m a.s.l. and is characterised by a continental summer-dry climate (Altermann et al., 2005). The soil type is Haplic Chernozem which is very fertile and consists of a thick humus horizon with a high water-retention capacity.
The natural vegetation of this area is mixed broad-leaved forest, but the area has been converted to agricultural land since the beginning of human settlement due to the high fertility of this soil type. The site had been used for agriculture until 2012 at which point it was converted to a grassland for two years until being ploughed to prepare the site for the establishment of the MyDiv Experiment.
Management
All plots are covered with a black, water-permeable weed tarp. This shall minimise weed growth and, thus, competition with saplings as well as the establishment of mycorrhizal fungi associated with other plants than tree saplings (Ferlian et al., 2018). The tarp will be removed as soon as a closed tree canopy develops. Trees were replanted after each survival assessment in the first two years. Weeds are removed from plots every year in summer. The grass paths of the site will be ploughed and resown once every few years in the future to disrupt potential hyphal networks between plots. Several live traps, posts for predatory birds, and fox tunnels underneath the fences were set up to monitor activity of voles and decrease their densities, respectively.
Trees have not been thinned or pruned in the first years of the experiment. However, once the dominance of fast-growing trees starts to become apparent and to outcompete subordinated ones, we will implement actions to preserve the experimental design.
References
Altermann M, Rinklebe J, Merbach I, Körschens M, Langer U, Hofmann B. 2005. Chernozem - Soil of the Year 2005. Journal of Plant Nutrition and Soil Science 168: 725-740.
Ferlian O, Cesarz S, Craven D, Hines J, Barry KE, Bruelheide H, Buscot F, Haider S, Heklau H, Herrmann S, Kühn P, Pruschitzki U, Schädler M, Wagg C, Weigelt A, Wubet T, Eisenhauer N. 2018. Mycorrhiza in tree diversity–ecosystem function relationships: conceptual framework and experimental implementation. Ecosphere 9:e02226.
