Dryland Ecosystems

Science Center Objects

Drylands are arid and semi-arid zones around the world where water resources are scarce. In the U.S., 40 percent of the land is considered dryland. USGS scientists are researching how predicted climate changes in dryland ecosystems--increases in temperature and declines in precipitation--will affect vegetation and wildlife in these areas as well as the ecosystem services they provide.

Drylands make up about 40 percent of the land in the U.S. By definition, drylands are areas where precipitation is less than two thirds of potential evapotranspiration. In other words, in a dryland ecosystem, the amount of potential moisture evaporated back into the atmosphere from plants and soil is greater than the amount of precipitation received by that region. Because dryland regions occupy so much of the land in the U.S. and the world, changes to these regions may impact global climate regulation.

The USGS climate change team as well as the Intergovernmental Panel on Climate Change have determined that drylands are one of three regions most vulnerable to climate change. Current predictions show a temperature rise of up to 10o F and up to a 20 percent decline in precipitation in dryland regions. USGS scientists are researching how these changes will impact the wildlife and vegetation that depend on drylands as well as how these changes will affect the global climate. Current research includes:

Climate change and ecohydrology in temperate dryland ecosystems: a global assessment

Biocrust, Birds of Prey NRCA near Boise, ID. (Public domain.)

We are integrating a proven soil water model with daily weather data from temperate dryland ecosystems across the globe to characterize potential future hydrologic changes in these water-limited ecosystems. A group of ecologists and hydrologists with experience in dryland ecosystems from around the globe will help parameterize and validate the model, and interpret the results. Outcomes from this workgroup will include insights about important commonalities, uncertainties, and vulnerabilities of dryland ecosystems and estimates of current and potential future ecosystem water balance and water availability in global temperate dryland ecosystems.

Completing the dryland puzzle: creating a predictive framework for biological soil crust function and response to climate change

Drylands are integral to the Earth system and the present and future of human society.  Drylands encompass more than 40% of the terrestrial landmass and support 34% of the world’s human population. Biocrusts are the “living skin” of Earth’s drylands, sometimes dominating the ground cover and figuring prominently in ecosystem structure and function. Biocrusts are a biological aggregate of cyanobacteria, fungi, algae, lichens and mosses in the surface millimeters of soil. By aggregating soil, biocrusts make sediment less erodible. They also strongly influence the water runoff-infiltration balance. In some ecosystems they generate runoff, whereas in other systems they enhance water capture. We have assembled a team of dryland experts spanning a variety of disciplines to address two broad questions: 1) What factors control the degree to which biocrusts contribute to key ecosystem functions (vascular plant success, water capture and redirection, and soil stability)?; and 2) How is global change likely to affect the function, distribution and diversity of biocrusts?

Image: Colorado Plateau
Colorado Plateau (Credit: USGS. Public domain.)

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

We are addressing significant uncertainties in our understanding of how vegetation and soil nutrient cycles in semi-arid and arid landscapes will respond to future climate and land use change. We will do this by analyzing and synthesizing historic vegetation transects and data on ecosystem processes (e.g., nitrogen (N) and C cycling) in grazed and ungrazed landscapes in different geomorphic settings. We will experimentally manipulate precipitation inputs to document the impacts of projected climate change. We will also characterize ecosystem processes in grassland never grazed by livestock to provide a benchmark for our manipulated grasslands. Lastly, we will use dryland photos that are up to 100 years old and repeat them to document changes in different plant communities in various landscape settings and climatic regimes. 

Sources, compositions, and effects of atmospheric dust from American Drylands

We are measuring past and ongoing changes in dust sources, flux, and composition in the American West to understand the effects of atmospheric dust on pressing national and global issues of snowmelt acceleration, air quality, and human health. We are developing the capability to forecast future dust emission/deposition and effects on the basis of  episodes of accelerated aeolian activity recorded in Quaternary and historical deposits.