DFG Research Group Forest Floor (DFG FOR 5315)

	Functioning, Dynamics, and Vulnerability in a Changing World

 The forest floor (FF) is the interface between above- and belowground parts of forest ecosystems. It provides habitat for a wide range of organisms, serves a seedbed and growth substrate for vegetation and acts as a central ecosystem hub where organic matter, nutrients, water and gases are stored, absorbed and transformed. As such, FF properties reflect complex interactions between biotic and abiotic ecosystem components, especially those related to microclimate and nutrient supply. An impact of climate warming on FF and associated services is likely especially in temperate regions where small changes in control variables may induce shifts from organic layer-dominated to mineral soil-dominated forests. Our RU focuses on analyzing the causal links between controls, properties, and ecosystem services of FFs. These links will enable (i) the determination of the service fulfillment through the FF in comparison to mineral topsoil, (ii) an assessment of FF vulnerability under climate warming and (iii) the use of FF properties as indicators for service fulfilment under given climatic conditions and properties of the mineral soil. These goals are directed by the overall hypothesis of the RU: Forest Floor properties of European beech forests are shaped by adaptations of organisms to the nutrient status of soils. The influence of climate warming on FF services depends on the interactions with these adaptations. This hypothetical framework will be implemented through specific hypotheses of 11 individual projects in close cooperation by focusing on combined phosphorus (P) and temperature impacts in European beech (Fagus sylvatica) forests admixed with Norway spruce (Picea abies) and sycamore maple (Acer pseudoplatanus). Twelve study sites allow the investigation of the interacting controls air temperature and P level of soils. At these sites, we will conduct 13C, 15N, 2H litter labelling experiments for process tracing and quantification and we will address nutrient, carbon and water dynamics. Our research will be complemented by studies addressing tree seeding experiments, microbial communities, soil fauna food webs, and root- and mycorrhiza-driven processes. Time-series analyses of existing data and ecological modelling will support process understanding, upscaling and scenario estimates.