The Effect of Infrastructure on Social-Ecological System Dynamics: Provision Thresholds and Asymmetric Access

For several millennia, humans have created built environments to harness natural processes for their benefit. Today, human-environment interactions are mediated extensively by physical infrastructure in both rural and urban environments. Yet studies of social-ecological systems (SESs) have not paid sufficient attention to how infrastructure influences coupled natural and social processes. This misses an important point: critical infrastructure is often a public good that depends on cooperation of the agents who share it. Using a model of an irrigation system (the most ancient of public infrastructure systems) as a testing ground, we found that two properties of infrastructure, threshold of provision and asymmetric access to benefits, greatly influence SES sustainability. Asymmetric access to benefits induces regimes of economic inequality. High thresholds suppress economic inequality, but at the cost of increased likelihood of system collapse. Low thresholds help to avoid system collapse, but may make the system more vulnerable to economic inequality and socioeconomic stresses. Understanding how small scale irrigation SESs may respond to such globalization-related stresses is relevant for agricultural policy and our results provide some general guidance in this regard. Studies of social-ecological systems (SESs) have typically focused on an ecosystem as their primary non-social component (9, 19, 32). The implicit assumption is that humans interact with natural systems without much mediation. This assumption may be true for some types of systems, like wildlife reserves. But it obviously is not always true. In many sustainability problems of great importance, a third element—built environment (or infrastructure)—heavily mediates between human-environment interactions. The importance of infrastructure in SESs was recognized early on in the pioneering work of Clark and Munro on how features of infrastructure such as the irreversibility of investment in fishing boats affect the dynamics of SESs (10). With globalization, the importance of built infrastructure will likely become ever more important. For example, the fossil-fuel-based infrastructure systems are the medium through which human actions cause climate change. Global food security depends on irrigation infrastructure through which farmers obtain water. And the resilience of urban systems to natural hazards often depends on engineered structures such as levees, roads, or buildings. Infrastructure also often requires inputs of collective human effort to be operational; in return, it allows humans to reap benefits from natural processes. In mediated systems, infrastructure fundamentally shapes the endogenous dynamics of coupled natural and social processes (3,23). What are the characteristics of infrastructure that may facilitate or constrain the sustainability of SESs? This study examines that question using a simple model of an