Globally, regime shifts from grasslands to shrublands (i.e., desertification) in arid and semiarid ecosystems are thought to be irreversible, similar to state changes in other ecosystems. The consequences of desertification, including loss of soil and nutrients to wind and water erosion, reductions in air quality, and decreases in forage and plant production, impact nearly one-fourth of the world’s human population. Here, we ask if directional climate change provides an opportunity to reverse this conversion in the Chihuahuan Desert of the Southwestern US. Although warming is predicted globally, there is uncertainty in both the magnitude and direction of change in precipitation for dryland regions. We compare historical dynamics based on >140 years of landscape change (1858-present) with 19 years (1990-2008) of detailed ecosystem responses under a variable climate to predict future responses under either a directional increase or decrease in rainfall.

Results/Conclusions Our data suggest that a long-term decrease in precipitation will accelerate current desertification trends with continuing loss of productive and diverse grasslands. On the contrary, a multi-year increase in precipitation can act to convert degraded shrublands to savannas containing mixtures of shrubs and grasses, and potentially a return to grasslands in the future. Because this regime shift reversal is not predicted based on historical drivers, our assumptions about ecosystem dynamics in the face of global change need to be re-examined, and new strategies need to be developed to take advantage of opportunities provided by future climates.