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Ökosystem-Resilienz unter Klimawandel - Wirkung und Interaktion von stabilisierenden Mechanismen in mediterranen Ökosystemen

Fachliche Zuordnung Ökologie und Biodiversität der Pflanzen und Ökosysteme
Förderung Förderung von 2014 bis 2019
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 263483514
 
Erstellungsjahr 2019

Zusammenfassung der Projektergebnisse

Ecosystems are known to exhibit buffer mechanisms that reduce the impact of disturbances on vegetation and that prevent the system from easily shifting from one state to another. Buffer mechanisms can occur on the level of the population (e.g. demographic processes), on the level of the community (e.g. substitution of one species by another with a similar function), or on the level of the landscape (e.g. refuge sites to survive stressful conditions). Simultaneously acting buffer mechanisms lead to the resilience of an ecosystem, which is defined as the ability to resist to stressors, to recover from disturbances and thus to persist. Therefore, the study of specific buffer mechanisms allows to mechanistically understanding resilience. Dryland systems, such as Mediterranean type ecosystems (MTEs), are characterized by stressful conditions and regular disturbances, such as droughts and wildfires. Therefore, they have evolved various buffer mechanisms to cope with these conditions. However, disturbance regimes in drylands are currently changing due to anthropogenic influences. Thus, the aim of the project was to determine (i) which buffer mechanisms exist under present conditions to allow for persistence and (ii) if current buffer mechanisms will also stabilize the ecosystem under future conditions or whether their capacity will be exceeded. Since the complexity of ecosystems poses a challenge to study buffer mechanisms with empirical methods, simulation models offer a way forward. They allow for systematic testing of the role of buffer mechanisms in different contexts, such as different disturbance regimes, but also on different levels of the ecosystem (individual, population, community, landscape). We used a suite of ecohydrological models that describe the coupled dynamics of water and vegetation to evaluated different known buffer mechanisms at various ecological levels of drylands. Particularly, we assessed (i) the ability of different demographic processes to buffer a plant population against wildfires and changes in their frequency, (ii) the role of species diversity and composition to buffer vegetation cover against changing water availabilities and (iii) the potential of landscape heterogeneity to buffer against drought impacts and grazing pressure under current and future climate. Our results show that buffer mechanisms exist at multiple levels of the ecosystem, i.e. from the individual plant to the landscape. However, we also found that these buffer mechanisms are only partly stable under future conditions (RCP4.5 and RCP8.5), in which we expect a higher frequency of drought years. For example, in our study system of a MTE in Western Australia the buffer capacity of canopy seedbanks, which gradually build up after fire events and thus allow for massive recruitment after the next fire event, will be exceeded under drier conditions, since demographic processes will be slower and fires more frequent. However, our simulations at the landscape scale show that these species can partly be substituted by less fire-prone species, especially in heterogeneous landscapes offering more diverse abiotic conditions. Thus, a diverse community and a diverse landscape can act as additional buffer mechanism, however, only for specific stressor combinations. These results clearly show that the strength of buffer mechanisms is context dependent. Our results emphasize the important role of buffer mechanisms to sustain ecosystem functioning. A potential application would be to increase the focus on buffer mechanisms for the management of ecosystems, i.e. to maintain buffer mechanisms. However, whether a mechanism will function as a buffer is context dependent, and future research should systematically assess this context-dependency to reliably assess the capacity of buffer mechanism to stabilize ecosystems against global change impacts.

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