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Accueil du site → Doctorat → Allemagne → 2009 → Impact of climate change and stocking rates on pasture systems in SE Morocco – An Application of the SAVANNA Ecosystem Model

Rheinischen Friedrich-Wilhelms-Universität Bonn (2009)

Impact of climate change and stocking rates on pasture systems in SE Morocco – An Application of the SAVANNA Ecosystem Model

Roth Andreas

Titre : Impact of climate change and stocking rates on pasture systems in SE Morocco – An Application of the SAVANNA Ecosystem Model

Auteur : Roth Andreas

Université de soutenance : Rheinischen Friedrich-Wilhelms-Universität Bonn

Grade : Dr. rer. nat. 2009

Résumé
Extensive sheep and goat grazing provides the main income for population in Morocco’s semi-arid to arid areas where rainfall does not permit cropping without irrigation. As processes of vegetation dynamics cannot be assessed via short-term approaches, modelling grazing and biomass productivity may provide better information for planning the sustainable use of these ecosystems. Southern Morocco has faced decreasing annual rainfall over the last two decades, with a strong impact on the sustainability of the regional ecosystems. Increasing herd sizes as a strategy to offset climate-induced variabilities in animal forage leads to an even more enhanced degradation. The aim of this work was to study the vegetation responses to a changing climate and to alternating livestock numbers. We used the spatially explicit, process-oriented ecosystem model SAVANNA© (Coughenour 1993) to formulise the reaction of the grass, shrub and tree plant functional types (PFT) for the period 1980-2000. The goal was to test its functionality and ability to simulate conditions based on elaborated plant, soil, and climate data. Next we evaluated a range of carrying capacity and climate change scenarios for the period 2001-2050 using the regional climate model REMO. The objective was to determine whether the simulation results obtained are anthropogenic or climate-induced. The outcomes showed on the one hand that the stocking rate highly influenced biomass production and inter-/ intra-PFT competition, thus reflecting the strong anthropogenic impact, and on the other hand that the climatic impact was weaker. However, together, the stocking rates and the increasing variability of rainfall introduced by the IPCC scenarios largely affected biomass production in all scenarios. All three PFT’s aboveground net primary production (ANPP) values remained constant or even decreased. Animal energy balances showed a high sensitivity to temporal variations in biomass. A high temporal variability was observed for nitrogen content in plants. Water condition related parameters, e.g. potential evapotranspiration, transpiration, and plant-available soil water are strongly related to rainfall, but showed a specific level of adaptation according to the predicted climate scenarios and livestock number. Under the assumptions made, the model simulated animal energy conditions, life-cycles, and forage values to an acceptable degree indicating both a sustainable resource use and human benefit. The simulation results obtained for plant growth parameters and water status agreed with outcomes from similar modelling approaches found in literature. At the end an adequate model structure was developed delivering future carrying capacity information by analysing the most important functional parts, floristic composition, spatial structure, and productivity of a grazed ecosystem in a water-limited environment.

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