Complexity of coupled human and natural systems

Integrated studies of coupled human and natural systems reveal new and complex patterns and processes not evident when studied by social or natural scientists separately. Synthesis of six case studies from around the world shows that couplings between human and natural systems vary across space, time, and organizational units. They also exhibit nonlinear dynamics with thresholds, reciprocal feedback loops, time lags, resilience, heterogeneity, and surprises. Furthermore, past couplings have legacy effects on present conditions and future possibilities. Coupled human and natural systems are in-tegrated systems in which people interactwith natural components. Although many studies have examined human-nature interactions (1–5), the complexity of coupled systems has not beenwell understood (6, 7). The lack of progress is largely due to the traditional separation of ecologi-cal and social sciences (8). Although some scholars have studied coupled systems as complex adaptive systems (9, 10), most of the previous work has been theoretical rather than empirical. An increasing number of interdisciplinary programs have been integrating ecological and social sciences to study coupled human and nat-ural systems (e.g., social-ecological systems and human-environment systems). Here, we synthe-size six case studies to demonstrate the approaches used and results found (Fig. 1 and table S1). These studies are on five continents: the Kenya