The economic literature on Payments for Environmental Services (PES) has studied extensively the behavioural factors that prevent farmers from signing PES contracts, even when the payments exceed the expected opportunity costs. This article provides a theoretical model of the role played by the interplay of descriptive and injunctive social norms in farmers’ decisions. When they choose to contribute voluntarily to an environmental public good, farmers may be driven by descriptive norms akin to conformity (do as the majority of their peers) as well as by injunctive norms (in line with what society expects them to do), which are the equivalent of a social injunction to act in favour of the environment. The interactions between these two social norms can yield multiple equilibria, depending on the relative weight of the descriptive norm (sensitivity to conformism) and of the injunctive norm (sensitivity to moral pressure) in the utility functions of farmers. More generally, our model can explain why social groups are sometimes trapped in low public-good-contribution equilibria, even when public subsidies to contributors are high. We make policy recommendations to help reach higher contribution equilibria, with a specific focus on the farm policy context.

关于环境服务付款（PES）的经济学文献已经广泛研究了即使在付款超过预期机会成本的情况下，农民也无法签署PES合同的行为因素。本文提供了一个理论模型，说明了描述性和禁令性社会规范在农民决策中的相互作用。当他们选择自愿为环境公益做出贡献时，农民可能会受到类似于合格的描述性规范（与大多数同仁一样）以及禁令规范（与社会期望他们的行为一致）的驱使。等同于采取有利于环境的社会禁令。这两个社会规范之间的相互作用可以产生多重均衡，取决于描述性规范（对顺从性的敏感性）和禁令规范（对道德压力的敏感性）在农民效用函数中的相对权重。更笼统地说，我们的模型可以解释为什么社会群体有时会陷入较低的公共利益贡献均衡，即使对贡献者的公共补贴很高。我们提出政策建议，以帮助实现更高的贡献平衡，并特别关注农场政策环境。