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Élever des bovins dans des paysages éco-efficients. Comprendre et modéliser le processus d’intensification dans les fermes d’élevage d’Amazonie orientale brésilienne

Abstract : After 50 years of agricultural expansion in Eastern Brazilian Amazon, environmental policy to reduce deforestation and a set of socio-economic drivers are putting constraints on extensive cattle ranching systems. In response, land use intensification has been gaining momentum as a way to improve livestock production in limited land areas and conserve forest. The process of land-use intensification is poorly understood in this region, particularly in its spatial dimension and in its contribution towards building eco-efficient landscapes, i.e. landscapes where practices and their spatial distribution optimize the use of natural resources. In this regard, the purpose of this research is to document and model the interactions between cattle ranchers’ decisions, landscapes and natural resources in a diversity of cattle farms.Firstly, we conducted a field research in two livestock-oriented regions of Pará state, Paragominas and Redenção. Drawing on interviews, landscape and farm trajectories analysis, we characterized six patterns of intensification, studied what perceptions cattle ranchers have on certain types of natural resources and described the effects of land-use management on such resources. Secondly, we developed an Agent-Based Model to simulate over 20 years the effects of intensive farming strategies on landscape and their natural resources, and assess the feasibility of adopting such management in various agrarian situations. We used the model to compare two scenarios of intensification: one semi-intensive solely based on improved pasture managenement and one intensive based on crop-livestock integration and irrigation.The results show that the process of intensification has led to a spatial rearrangement of land uses. Cattle ranchers prefer to intensify fields with the best biophysical conditions for forage production, as well as those closest to and most accessible from the farmstead. The intensification strategies aim at enhancing the use of multiple natural resources (topography, soil fertility, soil drainage, access to surface and groundwater for irrigation) and optimizing land-use configuration at farm scale. By contrast, during the colonization period, land-use organization was much less correlated to the spatial distribution of natural resources (except for soil fertility from forest ash and surface water), the main goal of farmers being land appropriation. Nevertheless, choice of farming practices and their spatial location differ among farms and according to the degree of heterogeneity of biophysical conditions. Moreover, simulation results show that the process of intensification can reduce the area necessary for animal production. Thus, cattle ranchers can increase herd size while sparing land for forest regeneration. However, low labor availability limits the spatial extent of land-use intensification at farm scale. In terms of landscape dynamics, cattle ranchers locate land-uses according to geomorphological units differently, which leads to various spatio-temporal dynamics of natural resources.Reconciling cattle ranching production and forest conservation in eco-efficient landscape remains an important challenge for Brazilian Amazon. The findings illustrate the importance of assessing the landscape areas most suitable for agricultural intensification and for conservation drawing on knowledge about cattle ranchers projects and the effects of their practices and spatial location on natural resources. Several opportunities and challenges are identified to tackle such challenge. New research perspectives related to decisions understanding, modeling and extension of the scale of analysis are proposed in order to take into account the influence of external factors on decisions and include more ecological and social interactions.
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Sophie Plassin. Élever des bovins dans des paysages éco-efficients. Comprendre et modéliser le processus d’intensification dans les fermes d’élevage d’Amazonie orientale brésilienne. Agronomie. Institut agronomique, vétérinaire et forestier de France, 2018. Français. ⟨NNT : 2018IAVF0028⟩. ⟨tel-02592197⟩

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