Drought and grazing impacts in semi-arid rangelands: Testing a novel trait-based conceptual framework

• Applicants: Professorin Dr. Bettina M.J. Engelbrecht, since 6/2021; Professorin Dr. Katja Tielbörger
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems
• Term: from 2016 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 319233647

Increases in drought and land use are among the most important global change drivers, particularly for dryland ecosystems. Semi-arid rangelands provide important ecosystem services and are predicted to be highly vulnerable to global change. Drought and grazing resistance have been assumed to converge (Generalized Grazing Model), so that species/communities in dry areas are both grazing and drought resistant. However, the generality of this model has been called into question by newer studies in semiarid rangelands dominated by winter annuals.We developed a novel trait-based conceptual framework that can resolve the apparent inconsistencies. Winter annuals display a substantially different strategy to cope with drought than perennials: they are drought escapers and survive the long summer drought in the seed bank. Associated with this distinct strategy are differences in underlying traits. Furthermore, even within winter annuals, there should be a wide range of trait expressions. We hypothesize a trade-off between traits associated with a drought escape strategy ('fast traits'), and traits for grazing tolerance and avoidance ('slow traits'), which lead to more negative impacts of grazing in annual species/communities in drier sites and more negative impacts of drought in wetter sites.To test the proposed framework we will use a steep rainfall gradient in the Eastern Mediterranean as a model system. We will assess over 30 physiological, morphological and life history traits related to drought and grazing resistance in 40 species with known distribution across the rainfall gradient, and combine them with survival and abundance data from in situ long-term drought and grazing experiments. This will allow to determine the key traits underlying drought and grazing resistance, and evaluate their relationships (convergence vs. trade-offs). Our study will for the first time 1) provide a comprehensive functional trait approach of winter annuals at the community level, and 2) explicitly link traits, whole plant performance, long-term community responses, and distribution patterns, filling an important gap in the basis of trait-based plant ecology. The proposed project will have the potential to transform our understanding of the interaction of drought and grazing, and substantially improve projections of consequences of global change.

• DFG Programme: Research Grants
• Ehemalige Antragstellerin: Professorin Leonor Alvarez-Cansino, Ph.D., from 10/2019 until 5/2021