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Responses of plant performance and functional diversity along a climate and land-use gradient in Mongolia

Subject Area Ecology and Biodiversity of Plants and Ecosystems
Term from 2014 to 2018
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 239358027
 
Final Report Year 2018

Final Report Abstract

Understanding responses of ecosystem processes to climate and land use change is a key challenge in ecology under both theoretical and applied aspects. So far it is not fully understood, however, how climate and land-use jointly affect ecosystem processes and services such as biomass production. In this project, we investigated the responses of ecosystem processes across climate and land use gradients, focusing on within and between species variability in plant traits, floristic and functional plant community patterns as well as biomass production. More specifically, we established 15 study sites along a 600 km precipitation gradient (104 - 248 mm) in the steppes of Mongolia, and perpendicularly run land-use intensity transects to answer the following questions: (1) What are the characteristics of land-use and climate along large-scale gradients in the Mongolian steppes, and how do grazing patterns interact with climatic gradients? (2) What are the relative effects and their interactions of land-use and climate on growth performances of selected focal species? (3) What are the relative effects and their interactions of land-use and climate on floristic as well as functional plant community patterns? (4) What are the relative effects (and their interactions) of land-use, climate and species as well as functional composition and diversity of the resident community on the responses of selected target species and their traits? Building on two successful field campaigns in 2014 and 2015, our project marks one of the first major endeavors to analyze at a large scale a climatic gradient that contains local scale grazing gradients within rangelands. By initially comparing the trait composition of three pairs of congeneric species across the precipitation gradients we could show unimodal relationships between most of the species’ traits and mean annual precipitation (MAP), and also demonstrated strong associations between species abundances and trait values. However, our results also highlight that species may differ, and even have opposite trait responses along the precipitation gradient. Focusing on 20 focal species, we investigated the interacting effect of precipitation and grazing intensity on patterns of intraspecific trait variability (ITV). We could show that ITV was most prominent for specific leaf area (SLA) and stomatal pore area index (SPI) under moister conditions, confirming the hypothesis that with decreasing MAP, ITV should become less prominent as climateinduced stress overrides the effect of disturbance by grazing. Accordingly, also the magnitude with which species change their trait values increased with increasing precipitation when focusing on the traits canopy height, SLA and SPI. However, this was not a general pattern as trait variability of the species over all traits increased with increasing precipitation for three species only. Finally, we could show that in a year not strongly deviating from mean climate conditions, all trait values were largely influenced by grazing. In contrast, in a year with extreme weather events, MAP largely affected sizerelated traits, and seasonal variation of precipitation determined the eco-physiological traits. On the community level, we found pronounced differences in community composition along the precipitation gradient, revealed climate-related grazing effects on species diversity and also found different grazing indicator species along the transect. In the dry non-equilibrium (NEQ) rangelands, grazing effects were limited to sacrifice zones and environmental filtering dominated vegetation composition. In the moist equilibrium (EQ) systems, resource availability was less important but grazing more strongly affected community responses and thus the presence of grazing-tolerant species. Also with respect to the functional community composition, we could show that grazing effects were limited to sacrifice zones in NEQ environments, while functional diversity changed across the whole grazing gradient under EQ environments. Biomass patterns were similar, with the effect of grazing being more important under equilibrium conditions, and playing a small role under non-equilibrium conditions. Hence, community patterns in terms of biodiversity, traits and biomass all confirm a lower impact of grazing under drier, non-equilibrium conditions, highlighting the importance of variable climate for ecosystem dynamics. Our results will eventually feed into the development of integrated models projecting shifts in species and biodiversity as well as biomass production in arid and semi-arid regions in the context of changing climate and grazing regimes.

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