The usual state of affairs in nature is one of populations fluctuating around some trend or stable average. Occasionally, however, this scenario is interrupted by an abrupt shift to a dramatically different regime, as when the populations of many species suddenly jump to different abundances in synchrony in the open ocean. The obvious intuitive explanation for such changes in nature is the occurrence of a sudden large external impact. However, theoreticians have long stressed that this need not be the case. Even a tiny incremental change in conditions can trigger a large shift in some systems if a critical threshold known as "catastrophic bifurcation" is passed. Intuitively, this is like the tipping over of an overloaded boat when too many people move to one side. A question of interest is whether such tipping points also exist in actively managed ecosystems, like irrigated rice paddies.
In spring 2011, a pilot study of traditional, small-scale irrigation systems (called subaks) on the Indonesian island of Bali produced the first empirical evidence for the presence of multiple regimes in an actively managed social-ecological system. One group of four subaks responded confidently to economic and environmental challenges, while a second group of four experienced a rapid decline. Subaks have existed on Bali since the eleventh century, but most are now at risk, and last year a thousand hectares of terraced fields went out of production. Signs that the subak system is under severe threat led to a proposal from the Government of Indonesia to create a UNESCO World Heritage Cultural Landscape to support the subaks. For the World Heritage to succeed, it is vital to understand what causes subaks to tip from one regime to another. This project will train Indonesian researchers to use the new multi-scale analytical methods developed for the pilot study, to investigate tipping points in 23 subaks. This study will also evaluate the potential of the new methods for understanding critical transitions in other social-ecological systems.
