Global change effects on forest understorey: how do interactions between drought and land-use intensity affect water, carbon and nitrogen cycling?

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Climate change is predicted to severely affect precipitation patterns across central Europe. The forest un-derstorey has not been subject to an extensive investigation with respect to climate change, yet, even though it is playing an important role in natural regeneration and forest succession. We propose here to es-tablish roof systems in forest plots in all three Exploratories and to study biogeochemical and hydropedologi-cal processes in response to reduced precipitation, and their interaction with forest land use type and the diversity of the forest understorey and of soil biota. Our research is focused on the direct and indirect effects of drought on different parts of the forest understorey system and the consequences for plant growth. We will address the effects of soil hydrological structures and functions and precipitation regime on the water and carbon balance of plant species and the resulting community effects in the manipulation experiments across land-use and biodiversity gradients. We will also take into account direct drought plus plant diversity effects on the microbial community structure and function and address the biotic feedback on soil structure and thus hydrological functions. The project will consist of five work packages (WPs), three of which are planned to start immediately, and the other two WPs to start after 3 years. The three WPs in the first phase will cover responses to drought at the level of individual plants and the herb layer plant community and vegetation change (WP1), drought effects on soil structure (WP2) and the interaction between plant function-ing/microbial community structure and soil hydrological properties (WP3). Work packages four and five are interested in longer-term changes of plant rooting patterns, nutrient uptake and in data on ecosystem effects to construct and validate ecosystem models.