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In this article, the introduction of Short Rotation Coppices of Eucalyptus into specialized cash crop farming systems is analyzed at both individual and local scale. The area studied is located in Toulouse urban area, which raises the problem of competition between farming, forest and urban activities. À methodological framework is built up with two disciplinary approaches. In a first step, we assess the financial incentives and the possible transaction costs linked to the contracts offered by retailers to farmers, in order to encourage them to plant trees. In a second step, we propose to enlarge the analysis scale beyond the supply chain and to explore, with a mediation tool, the possible institutional arrangements, at local scale, that could diminish transaction costs and increase the acceptability of the plantation.