A complex adaptive systems model of labor reciprocity and normative reasoning in swidden agriculture

Swidden (aka "slash-and-burn") agriculture is a prototypical coupled human and natural system and understanding the social, cultural, and environmental factors shaping the trajectories of swidden forests is essential to mitigate climate change and ensure equitable collaboration between scientists, planners, and Indigenous communities. Despite this, mathematical models integrating its social and ecological dynamics are rare. Here, we use complex adaptive systems theory to develop a model where individuals rely on labor exchange driven by reciprocity, and on normative reasoning that can lead to sanctions. Our results identify three emergent regimes: low-intensity swidden, sustainable high-intensity swidden that maximizes ecosystem services and harvest returns, and deforestation. We show that sustainable high-intensity swidden evolves if labor reciprocity and normative reasoning are balanced: helping behavior should be significantly conditioned by normative reasoning to prevent over-harvesting, while reciprocity is necessary to prevent excessive sanctioning. We find that the sustainable high-intensity swidden regime is robust to changes in group size, is resilient to environmental shocks, can evolve under various models of forest ecology, and is most productive for both forests and farmers when the balance of labor reciprocity and normative reasoning results in an intermediate scale of forest disturbance. Overall, we illuminate the importance of Indigenous social norms and customary practices related to swidden labor in maintaining sustainable and intensive swidden agriculture.