Hub-and-spoke social networks among Indonesian cocoa farmers homogenise farming practices

Smallholder farms support the livelihoods of 2.5 billion people and their decisions on how to manage their land has profound consequences for the environment and the food security of billions of people. However, farmers' values, norms and resulting management practices are usually not formed in isolation. Triangulating multiple analytical, modelling and simulation methods, we investigated if and how social influence exerted through peer-to-peer information exchange affect soil nutrition management among 2734 Indonesian smallholder cocoa farmers across 30 different villages. The results show that the relational structures of these village-based social networks strongly relate to farmers' use of fertiliser. In villages with highly centralised networks (i.e. hub-and-spoke networks where one or very few farmers holds disproportionately central position in the village network), a large majority of farmers report the same fertiliser use, and that practice is typically to avoid using fertilisers. By contrast, in less centralised networks, fertiliser use varies widely. The observed community-level distributions of fertiliser use can be most closely reproduced through simulations by complex contagion mechanisms in which social influence is only exerted by opinion leaders that are much more socially connected than others. However, even such leaders' abilities to influence others to change fertiliser use may be limited in practice. The combination of our quantitative and qualitative findings provides significant policy implications for development programs targeting smallholder farming communities. An important practical lesson is that common interventions which primarily engage socially central farmers may not be effective in stimulating desired transitions in social-ecological systems.