Ecohydrological feedback mechanisms in arid rangelands: Simulating the impacts of topography and land use |
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| Authors: | Alexander Popp Niels Blaum Florian Jeltsch |
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| Institution: | 1. Institute of Animal Science, 2232 Kostinbrod, Bulgaria;2. CIMO Mountain Research Centre, School of Agriculture, Polytechnic Institute of Braganza, Campus de Santa Apolónia, 5300 Bragança, Portugal;1. Department of Physical Geography and Ecosystems Analysis, Lund University, Sweden;2. Institute of Geology at Tallinn University of Technology, Estonia;3. Department of Geography, University of Tartu, Estonia;4. Department of Geology, Lund University, Sweden;5. Institute of Ecology, Tallinn University, Estonia;6. Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Estonia;1. Research Ecologist, USDA-ARS Rangeland Resources Research Unit, Fort Collins, CO 80526, USA;2. Assistant Professor, Department of Wildland Resources and Ecology Center, Utah State University, Logan, UT 84322, USA;1. National Program Leader, Rangeland and Grassland Ecosystems, Agriculture Water Security, USDA-NIFA, 1400 Independence Ave SW, Washington, DC 20250, USA;2. Regents Professor, Department of Natural Resource Ecology and Management, Oklahoma State University, Stillwater, OK 74078, USA |
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| Abstract: | The interaction between ecological and hydrological processes is particularly important in arid and semi-arid regions. Often the interaction between these processes is not completely understood and they are studied separately. We developed a grid-based computer model simulating the dynamics of the four most common vegetation types (perennial grass, annuals, dwarf shrubs and shrubs) and related hydrological processes in the region studied. Eco-hydrological interactions gain importance in rangelands with increasing slope, where vegetation cover obstructs run-off and decreases evaporation from the soil. Overgrazing can influence these positive feedback mechanisms. In this study, we first show that model predictions of cover and productivity of the vegetation types are realistic by comparing them with estimates obtained from field surveys. Then, we apply a realistic range in slope angle combined with two land use regimes (light versus heavy grazing intensity).Our simulation results reveal that hydrological processes and associated productivity are strongly affected by slope, whereas the magnitude of this impact depends on overgrazing. Under low stocking rates, undisturbed vegetation is maintained and run-off and evaporation remain low on flat plains and gentle slope. On steep slopes, run-off and evaporation become larger, while water retention potential decreases, which leads to reduced productivity. Overgrazing, however, reduces vegetation cover and biomass production and the landscape's ability to conserve water decreases even on flat plains and gentle slopes.Generally, the abundance of perennial grasses and shrubs decreases with increasing slope and grazing. Dominance is shifted towards shrubs and annuals. As a management recommendation we suggest that different vegetation growth forms should not only be regarded as forage producers but also as regulators of ecosystem functioning. Particularly on sloping range lands, a high percentage of cover by perennial vegetation insures that water is retained in the system. |
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