Understorey plant assemblages and primary production

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Understorey plant communities and wood-dependent bryophytes and lichens are major components of temperate forest diversity and play an essential role for multiple ecosystem functions such as primary productivity, microclimate regulation, decomposition or habitat provisioning. There is much evidence that these taxa strongly respond to changes in habitat conditions across spatial and temporal scales, leading to shifts in community composition and diversity at the local (α-diversity) scale. Thus, modifications of the biotic and abiotic environment by enhancing structural complexity at the patch (ESC treatments) and district (i.e. landscape) level (ESBC treatments) are expected to have important functional consequences for these species assemblages and related ecosystem processes. However, the direction and magnitude of ESBC effects on taxonomic and functional β-diversity of understorey plant communities and wood-dependent cryptogams in real forest landscapes still remains unclear. The main objective of this subproject is to investigate to which extent a higher spatial heterogeneity of temperate forests via ESBC treatments increases the β-diversity of non-tree vascular plants, terricolous bryophytes, and lichens in the understorey vegetation as well as of wood-dependent bryophytes and lichens. In the case of non-tree vascular plants we furthermore intend to analyse how this feedbacks to their above- and belowground functioning in terms of biomass productivity. We will sample the understorey vegetation and wood-dependent bryophytes and lichens in all patches. This allows us to extend a time series which has been started in the ESBC-treated districts during the years 2016 to 2018. Leaf, root and plant size-related functional traits of non-tree vascular plants will be measured in order to calculate functional diversity metrics at α- and β-scales. In addition above- and belowground biomass of the understorey vegetation will be determined to estimate productivity. We will test the hypotheses that the increase in spatial heterogeneity caused by ESBC treatments will enhance the taxonomic and (whole-plant) functional β-diversity of non-tree vascular plants, terricolous bryophytes, and lichens found in the forest understorey (Hypothesis 1) and that the increase in taxonomic and functional β-diversity positively affects the aboveground and belowground productivity of understorey plant communities at the district level (Hypothesis 2). For the whole research unit we will provide biodiversity data for vascular plants, terricolous as well as wood-dependent bryophytes and lichens. Additionally, we will measure traits of non-tree vascular plants to be added to the trait database. Our subproject will determine understorey primary aboveground and belowground productivity as an important ecosystem function, contributing to the multifunctionality analysis.