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ARS Home » Pacific West Area » Burns, Oregon » Range and Meadow Forage Management Research » Research » Research Project #437612

Research Project: Causal Factors of Exotic Annual Grass Invasion Across the Great Basin Sagebrush Ecosystem

Location: Range and Meadow Forage Management Research

Project Number: 2070-21630-003-13-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Sep 15, 2019
End Date: Sep 15, 2024

Objective:
Exotic annual grass invasion of sagebrush communities alters ecosystem function and processes, degrades wildlife habitat, and increases wildfire frequency and size. Exotic annual grasses are highly competitive with native vegetation, particularly seedlings, and thus can displace native vegetation. Exotic annual grasses dry out earlier than native vegetation and increase fine fuel loads and continuity, leading to increased fire probability. This has led to the development of an exotic annual grass-fire cycle in some areas. Invasion by exotic annual grasses has led to decreased rangeland forage production and resulted in over 300 sagebrush associated species being of conservation concern. Exotic annual grass invasion has severe economic effects; for example, federal fire suppression expenditure in FY 2017 approached $3 billion. Understanding the relative importance and variability of mechanisms that promote exotic annual grass invasion is critical to limiting invasion. However, information on the causes of exotic annual grass invasion is limited and largely anecdotal. We do know that perennial grass abundance is a key factor limiting exotic annual grasses, and factors that negatively impact perennial grasses are associated with increases in exotic annual grasses (e.g., overgrazing and fire). Site characteristics, however, influence how resistant a site is to annual grass invasion. How site characteristics and other possible explanatory factors interact to influence exotic annual grass invasion is unknown and thus, management is hampered by a lack of knowledge. Furthermore, the impact of exotic annual grasses likely varies by site characteristics and this information is critical in prioritizing management. The objectives of this research are to 1) Identify site attributes that make sites resistant to exotic annual grass invasion, and 2) Determine the interactive effect of disturbance with site attributes on invasion resistance. The results of this work will apply across the sagebrush ecosystem of the Great Basin.

Approach:
We will select up to 50 locations stratified across the sagebrush ecosystem in the Great Basin. At each location, we will select sites that occur on north, south, east, and west aspects as well as a flat site. We will measure vegetation cover and density by species at each site. We will record site characteristics including slope, aspect, soils, precipitation, elevation, climate, latitude and longitude, and vegetation community type. We will also determine disturbance history, in particular, fire history and grazing pressure. We will use a piosphere design to estimate grazing pressure based on distance from water. We will analyze the influence of site characteristics, disturbance history, and their interactions on exotic annual grass invasion using structured equation modeling. We will determine the effects of annual grass invasion using a space for time substitution design.