PARENT SESSION
Contributed Oral Session 12: Arid Lands: Plant Response to Precipitation
Monday, August 8, 8:00 AM - 11:25 AM, Meeting Room 520 B, Level 5, Palais des congrès de Montréal
How do grazing and stochastic rainfall affect vegetation? Insights from a simulation approach.
Puetz, Sandro1, Paruelo, José2, Weber, Gerhard1, Jeltsch, Florian3, Wiegand, Thorsten1, 1 UFZ Leipzig-Halle GmbH, Leipzig, Germany2 Institute for agricultural Plant Physiology and Ecology, Buenos Aires, Argentine3 University of Potsdam, Potsdam, Germany
ABSTRACT- Semi-arid and arid regions are endangered by desertification and degradation on a global scale. Most of the drylands are characterized by unpredictable and stochastic rainfall, so the effects of overgrazing may be masked by rainfall. Due to the stochastic rainfall, the strong dependence of vegetation on rainfall and the lack of empirical long-term studies on vegetation dynamics it is difficult to separate the effects of grazing and climate without using a modelling approach. We therefore use a simulation model to investigate how an interaction between and grazing and stochastic rainfall affects vegetation dynamics. To separate the natural and anthropogenic effects from each other we built a grid-based and individual-based simulation model which describes the dynamics of the dominant tussock grass species of a temperate semi-arid steppe, Festuca pallescens, under grazing in Northwest Patagonia (Argentine). The model operates at the scale where the grazing decisions take place and includes a biologically plausible grazing model. Further, it describes the impact of stochastic rainfall and grazing on the essential biological processes seedling establishment, growth, and mortality. We use a pattern-oriented approach to indirectly determine unknown model parameters and to calibrate the model to show the observed dynamics. In a second step we simulate the dynamics of the Festuca steppe under different stocking rates. An analysis of the simulation experiments reveals how stochastic precipitation affects demographic processes of the perennial tussock grass F. pallescens, how grazing triggers the demographic processes, and how grazing and stochastic rainfall interact. The separation of the natural and the anthropogenic effects on vegetation greatly advances our quantitative understanding of the grazing impact in drylands and provides robust arguments for the discussion of sustainable management of rangelands.
Key words: Grazing stochastic rainfall interaction, Semi-arid Rangeland, Spatially explicit individual based modelling, Vegetation degradation