1. Department of Geography, University of Zurich, Zurich, Switzerland
2. Department of Disturbance Ecology, University of Bayreuth, Bayreuth, Germany
3. Experimental Plant Ecology, Institute of Botany and Landscape Ecology, University of Greifswald, Greifswald, Germany
4. Department of Soil Biogeochemistry, Martin Luther University Halle-Wittenberg, Halle, Germany