Research:

Ecosystem consequences
of cheatgrass invasion
in the Great Basin
This large gas-exchange chamber is used to measure carbon dioxide and water vapor fluxes for sagebrush and other types of vegetation in the Great Basin Desert. Cheatgrass, a winter annual grass originally from Europe, has invaded the Great Basin and by increasing the fire frequency is replacing sagebrush and other native species. A large-scale transformation is underway in this ecosystem from perennial shrubland to annual grassland. Using this chamber and other techniques, we are trying to determine how this transformation will affect the carbon and hydrologic cycle of this vast area. Non-native grasses have been aggressively invading the sagebrush steppe ecosystem of the Western United States over the last century. Promoted by overgrazing and fire, this invasion has rapidly converted large expanses of native sagebrush shrubland to successional post-fire communities. Management and restoration practices have resulted in a mosaic of community types, dominated by non-native species including annual grasses, forbs and perennial bunchgrasses. However, repeated fires may cause cheatgrass to become dominant in most post-fire communities. Cheatgrass (Bromus tectorum L.) has become the most widespread noxious weed in Western North America, dominating or infesting over 80% of all public lands in Nevada. Changes in species composition and diversity caused by altered land use practices and invasive species may have important feedbacks on ecosystem processes. Since plant cover controls ecosystem function, this cheatgrass-driven landscape transformation will likely impact the timing and magnitude of carbon, water and energy exchange in the Great Basin.
The objectives our research are:
  • to determine how replacement of sagebrush with alien post-fire communities alters spatial and temporal patterns of ecosystem carbon, water and energy exchange at multiple sites in the northern Great Basin and
  • to investigate the role biotic and environmental factors play in controlling these fluxes. Using chamber-based methods and Bowen ratio energy balance approach, we quantified the surface fluxes of carbon, water and energy in adjacent sagebrush and post-fire communities at three sites across Nevada where the dominant non-native species and cover of cheatgrass in the post-fire community varied. 

Post-fire replacement of sagebrush with cheatgrass continues to degrade the grazing quality and reduce the diversity of plants and animals in the Great Basin. Current reclamation efforts have had very limited success reestablishing shrub steppe. Quantifying the effects of cheatgrass on the ET and soil water will provide an important foundation for future experiments designed to determine successional sequences after fire in the Great Basin, and to design appropriate strategies for restoring native sagebrush communities after large-scale disturbance.

Updated 10/28/03