Tipping points in rangelands: The scales of social-biophysical interactions

Ecological and socio-economic processes are driving many of the world’s rangelands beyond “tipping points” to degraded states, but we have a poor understanding of the mechanisms by which these processes are linked to each other. We argue that this is due largely to the lack of data on region-scale patterns. We review three key concepts guiding our approach to investigating rangeland degradation at regional scales. First, a mechanistic understanding of tipping points must be based on understanding cross-scale relationships in pattern-process interactions. One insight is that the scales at which we should look for significant patterns/processes (e.g., those that explain variation in vegetation and soil degradation) vary with context and are often broader than we implicitly recognize. Second, transitions to degraded states are strongly conditioned by climo-edaphic heterogeneity. We are only beginning to identify and quantify the key attributes that govern transitions and know little about how climate change will modify those relationships. Finally, it is widely held that human behaviors underlie the approach to tipping points and loss of resilience, but we have little systematic understanding of how variations in behavior affect them. In the U.S., for example, spatial patterns of control of public grazing lands established under the Taylor Grazing Act, the adoption of more stringent rangeland oversight policies (e.g., the National Environmental Policy Act), and changing motivations of landowners may have large and unrecognized impacts on transitions. Improvements to the tools and policies we use to react to tipping points in rangelands will require broad-scale, social-ecological approaches that are still nascent.