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Osnabrück Universität (2006)

Sustainable grazing management in semi-arid rangelands : an ecological-economic modelling approach

Müller, Birgit

Titre : Sustainable grazing management in semi-arid rangelands : an ecological-economic modelling approach

Auteur : Müller, Birgit

Université de soutenance : Osnabrück, Univ., Diss.,

Grade : Doktorgrades der Naturwissenschaften (Dr. rer. nat.) 2006

Résumé
The loss of utilisable rangeland in semi-arid areas, often termed as ”desertification”, results in enormous economic and social costs worldwide. Only adaptive management strategies are able to cope with these systems, which are largely driven by unpredictable and stochastic rainfall. Since grazing in semi-arid regions is characterized by strong feedback mechanisms between economic and ecological factors, global changes, such as new opportunities of economic risk management, affect the rangeland system as a whole. This study aims to contribute to the identification of basic principles for sustainable grazing management. It tackles the challenge of selecting suitable ecological and economic risk management strategies to cope with risky income without worsening the state of the pasture. The approach emphasizes learning from existing management systems through the use of ecological-economic modelling. Two apparently successful management systems in Namibia are used as a starting point for a broader analysis : the Gamis Karakul sheep farm and the land use system of the semi-nomadic Ova-Himba. Although these economic systems differ strongly (commercial rest-rotation farming versus opportunistic subsistence farming), their management seems to have similarities : the importance of pasture resting and of adapting livestock numbers to available forage. This PhD thesis contributes substantial insights about the relevance and functioning of pasture resting for sustainable grazing management in semi-arid regions. Assessment of the two case studies leads to the hypothesis that resting in the rainy season, particularly during wet years, is fundamental for ensuring pasture productivity under low regeneration potential of the vegetation. Additionally, the thesis highlights that resting during wet years acts as a risk reducing strategy, specifically buffering income variability in the short term while ensuring high pasture productivity in the long term. The study reveals that access to economic risk management strategies, such as rain-index-insurance, may change farmer’s behaviour. Therefore the preferences of the individual farmer, in particular his risk aversion and time horizon, are shown to be highly influential. These determine whether he will choose less conservative grazing strategies following access to insurance. The used approach - learning from existing apparently successful grazing strategies by ecological-economic modelling - offers a powerful tool for tackling new questions related to global change. The scope and the limits for generalizing the key factors discovered for sustainable grazing management can be easily detected under changing ecological, climatic and economic conditions

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