Drylands are highly vulnerable to climate and land use changes: what ecosystem changes are in store?

Statement of Problem:

Drylands comprise approximately 35% of Earth’s terrestrial biomes, with over 1 billion people depending on these landscapes for their livelihoods. In the U.S., drylands comprise about 40% of the landmass and 83% of Department of Interior managed lands (excluding Alaska). A substantial rise in temperature (~ 6°C) and changes in precipitation are predicted for these regions. These water-limited ecosystems are often characterized by low resilience to warming and drying, and therefore small environmental changes can have vast and unexpected ecological consequences. With large predicted shrifts in climate for dryland regions, impacts to wildlife, livestock, and human populations dependent on these resources are likely to be profound and widespread. As a result, drylands have been identified as one of three regions that will be most vulnerable to climate change by both IPCC and the USGS Climate Change team.

Why this Research is Important:

New understanding of climate change impacts on ecosystem processes produced by this effort are informing DOI and other federal, state, tribal, and private land management decisions aimed at mitigating effects of land change and increased aridity.  More specifically, new understanding regarding which plant species are likely to survive under future conditions can guide the selection of appropriate plant stock for restoration as well as enable us to predict the quality of available forage and habitat. By providing information to help distinguish ecosystem change due to climate alone from those changes attributable to land use, the results of this work are helping managers of complex, multi-use landscapes identify new management solutions. Our studies focus on the Colorado Plateau region, which covers 195,000 km² of northern AZ, northwest NM, western CO, and southern UT.  However, our findings will apply to a much larger area of the western U.S., in that many areas support the same plant species and have similar soils and climate.

Objective(s):

This project is addressing the following questions: 

1. What are the primary drivers of historic vegetation change in drylands of the western US?  How is resilience these ecosystems mediated by biological versus physical processes?   
2. How will plants and soils in dryland communities respond to long-term, moderate reductions in precipitation?
3. How sensitive are dryland grassland communities to extreme drought?  How does sensitivity change with the seasonality of drought (cold versus warm season)?  How do various drought scenarios alter grass-shrub dynamics in grasslands?
4. How do dryland grassland communities to respond to combinations of drought, disturbance, and grazing?  If grazing is deleterious, can altered timing of grazing help mitigate these impacts? 

Methods:

This project is addressing gaps in our understanding of how vegetation and soils will respond to future climates, land use, and the interactions between these factors. We will build this understanding using a several approaches, including:

1. Surveys of vegetation and soils fertility across lands with differing in land use history (grazing by domestic livestock);
2. Experiments in which we manipulate precipitation to simulate future droughts;
3. Using ecosystem simulation modelling; and 
4. Experiments where we simulate the interaction of grazing and drought.