Simulating spatial changes in vegetation-livestock interactions under different landscape structures: a multi-agent system applied to agro-pastoral territories

Sane M., Vayssières Jonathan, Grillot Myriam, Bah Alassane, Ickowicz Alexandre. 2016. Simulating spatial changes in vegetation-livestock interactions under different landscape structures: a multi-agent system applied to agro-pastoral territories. In : Proceedings of the 8th International Congress on Environmental Modelling and Software. Sauvage, S. (ed.), Sánchez-Pérez, J.M. (ed.), Rizzoli, A.E. (ed.). Toulouse : Université de Toulouse, pp. 507-514., 5 vol (1335 p.) ISBN 978-88-9035-745-9 International Congress on Environmental Modelling and Sofware (iEMSs 2016). 8, Toulouse, France, 10 July 2016/14 July 2016.

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Abstract : Free-range and common-grazing ruminants play a major role in the functioning and the provision of ecosystem services by agro- and silvo-pastoral ecosystems in sub-Saharan Africa. To assess how landscape structure affects the nature of environment-herd-services interactions, this paper describes a Multi-Agent System (MAS) that simulates daily herd movements in a dynamic environment. The model is used to study how the overall productivity of an agricultural territory is affected by the spatial organization of its different landscape units. The originality of this model lies in fine representation, in hourly time steps, of a herd's movements and activities over the seasons depending on changes in its environment. The herd is likened to a reactive agent with a global representation of its environment. It moves, grazes, drinks, rests and defecates. The model represents the spatio-temporal takeoff of biomass and animal faeces deposits. Grazing occurs between the moving, watering and resting phases, while defecation is continual. Biomass ingestion depends on its relative abundance in the explored plots, while the amount of faeces excreted depends on the amounts of biomass ingested the previous day. This paper describes the first use of the model on a choreme type environment representing a theoretical village territory typical of those found in West Africa. It comprises 5 landscape units: dwellings, compound fields, bush fields, fallows and rangelands. Two scenarios corresponding to 2 different landscape structures were simulated: alley fallows (Sc1), scattered fallows (Sc2). Most faeces deposits were in the fallows (sc1) or rangelands (sc2) in the wet season (4 out of 12 months) and in compound fields in the dry seasons (8 out of 12 months). Alley fallows (sc1) helped to intensify fertility transfers from rangelands to cultivated zones, thereby increasing productivity in cultivated zones (+26%) to the detriment of rangelands (-68%). The presence of ruminants in the territory therefore helped to i) enhance the positive effect of fallows and rangelands in renewing the fertility of cultivated soils and ii) maintain a system of concentric fertility rings with a decreasing fertility gradient from the core (=dwellings) to the periphery of the village (= rangelands). This modelling work thus helps to explain how landscape heterogeneity seen in African village territories is constructed.

Classification Agris : L01 - Animal husbandry
L02 - Animal feeding
F40 - Plant ecology
P01 - Nature conservation and land resources
U30 - Research methods

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