The advent of social-ecological system perspectives has led to new questions about the causes and consequences of global change. Nearly all research in rangeland ecosystems of the U.S. has focused on transitions in vegetation (such as grasslands to shrublands) casting human activities (especially livestock production) as an external driver of change. Here, we consider abrupt change in Southwestern rangelands from a social-ecological systems perspective. We consider the theory that abrupt changes in societal organization and environment are due to changes in multiple slow variables, including social factors, government policy, markets, and technology, interacting with abrupt “trigger” events, especially drought, that leads to acute limitations and longer-term reductions of perennial grass forage. We draw upon a number of data sources to characterize and explain social-ecological transitions over the last 160 years in southwestern New Mexico, and offer predictions about the next transition.
In the late 1800s, government policies to encourage settlement as well as access to foreign capital, alongside the proliferation of railroads and water developments, led to a rapid increase in livestock numbers and large cattle ranches (transition 1). Subsequent multi-year droughts and overstocking led to catastrophic livestock losses, reductions of perennial grass cover, and new government policies that promoted a transition to smaller ranching enterprises in the 1930s (transition 2). Since that time, severe droughts have led to additional loss of perennial grasslands and gradual shrub encroachment, alongside increased urbanization and recognition of environmental degradation. Recent livestock numbers are considerably lower than carrying capacities estimated in the mid-20th century. Ranch ownership has been unstable in the least favorable landscapes, associated with only patchy ongoing reduction of perennial grass cover. Predicted declines in regional water balance and increased interannual precipitation variability will again accelerate loss of perennial grasses, increase dominance by unpalatable shrubs, and reduce availability of harvested forages (hay) necessary for sustaining small-scale ranching operations. We predict that the next social-ecological transition will involve 1) the dissolution of some small ranching enterprises and aggregation of private and leased land into larger, corporate operations that may not emphasize livestock production, 2) increased use of public lands for renewable energy production and wilderness, and possibly the reorganization of public land leasing strategies, 3) the transformation of most remaining grassland areas to shrublands, and 4) the potential for greatly increased wind erosion rates and declining air quality for urban centers.