Importance of Seasonality for the Response of a Mesic Temperate Grassland to Increased Precipitation Variability and Warming
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Timing of precipitation events within the growing season and the non-uniformity of warming might be decisive for alterations in productivity and community composition, with consequences for ecosystem functioning. The responses of aboveground production, community composition, functional group and species evenness to altered intra-annual precipitation variability and their interactions with winter or summer warming were examined in European, mesic temperate grassland. Increased precipitation variability with an induced spring drought resulted in a 17% reduction in ANPP, and late drought reduced ANPP by 18% compared to regular rainfall patterns throughout the entire growing season. Winter warming increased ANPP by 12%, whereas summer warming showed no significant effect on biomass but decreased species richness. The effects of increased precipitation variability and warming on ANPP were independent of each other. Forbs benefited from high precipitation variability with spring drought events, likely due to reduced competitive pressure by decreasing, water stressed grasses. Increased precipitation variability coinciding with higher summer temperatures led to reduced species evenness and likely promoted the establishment of specialists and drought-tolerant species. Seasonality of climatic factors, here early versus late drought events in the high precipitation variability treatments, was important in driving shifts in community composition but not for decreases in ANPP. Non-uniform warming, here winter versus summer, affected the direction of response of both community composition and ANPP. Variability of resources is affecting ecosystem processes and species interactions. Recognition of seasonality and non-uniformity of climatic factors will improve predictions of plant performance and biotic interactions in response to climate change.
Keywordsclimate variability seasonality vegetation shift EVENT II experiment extreme weather event precipitation regime plant functional type non-uniform warming community composition aboveground productivity
The study was funded by the German Science Foundation (DFG JE 282/6-1), by the Bavarian State Ministry of the Environment and Public Health (ZKL01Abt7 18456), and by the ‘Bavarian Climate Programme 2020’ of the Bavarian State Ministry of Sciences, Research and the Arts within the FORKAST research cooperation ‘Impact of Climate on Ecosystems and Climatic Adaptation Strategies’. We thank E. Koenig, C. Schemm, S. Koenig, C. Pilsl, E. Straetz and numerous student workers and interns for their help during the field work. We thank Peter Wilfahrt and Joe Premier for proofreading the manuscript in terms of language and style and the anonymous reviewers for their helpful comments on an earlier version of this manuscript.
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