Do perennial bunchgrasses competitively exclude Bromus tectorum in post-fire rehabilitation?
Globally, wildfire size and frequency has increased in the last thirty years across numerous ecosystems. Models predict that trend to continue with increases in temperature and shifts in seasonal precipitation caused by climate change. In the western United States, these trends are exacerbated by invasive annual grasses that create a self-perpetuating fire regimes with frequent, large fires. The annual grass, Bromus tectorum (cheatgrass), has radically altered fire regimes in the Great Basin and contribute to the loss of sagebrush habitat. Controlling the expanding range of B. tectorum is key to maintaining existing sagebrush and successfully establishing sagebrush steppe vegetation and rangeland health in post-fire rehabilitation.
Attempts to synthesize the effects of post-fire rehabilitation in rangelands are hampered by the lack of research in these systems at landscape-scales. Research conducted in small field plots and common gardens suggest some perennial bunchgrasses may limit the growth, cover, or reproduction of B. tectorum, but the scalability of small-scale research across landscapes and post-fire treatment types is uncertain. Three perennial bunchgrasses commonly used in post-fire rehabilitationAgropyron cristatum (crested wheatgrass), Elymus elymoides (bottlebrush squirreltail), Poa secunda (Sandberg bluegrass)have been shown to reduce the productivity, growth, and/or reproduction of B. tectorum at the common garden or plot level, but their effectiveness over large scales is uncertain.
We propose to examine the distribution of B. tectorum and perennial bunchgrasses across plot, site, and landscapes scales on locations with and without post-fire rehabilitation using spatial analysis of photoquadrats. Sixtyfive sites are divided into treatment combinations that include varying fire (unburned or 1, 2,3 or 6 burns) and post-fire rehabilitation seeding (untreated, drill, aerial) histories. This work will complement research conducted by the student investigator on plant cover, density, and biomass using sites with a known fire and treatment history. The spatial analyses will allow us to address the following research questions: 1) Does seeding Poa secunda, E. elymoides, and A. cristatum after a fire reduce the dispersion of B. tectorum at the plot or site scale? 2) Is the spatial distribution of grass species consistent among sites across landscapes? The research proposed here will leverage existing research on public lands managed by the Bureau of Land Management (JFSP 11-1-2-30 and 14-1-1-07; NASA NNX11AO24G) to examine whether perennial bunchgrasses used in post-fire rehabilitation competitively exclude B. tectorum while accounting for fire and rehabilitation history.
The expected benefits of examining the dispersion patterns of these four species include: 1) improving our understanding of B. tectorum establishment after rehabilitation; 2) informing seed selection and relative species proportions that will increase the resistance of future rehabilitation efforts to B. tectorum invasion. The results from this research will be published in two peer reviewed journal articles and the results will be shared at annual meetings with managers at the Bureau of Land Management, USDA Agricultural Research Station, and US Geological Survey. All data will be archived and publicly available via the Fire Research and Management Exchange System (FRAMES) (http://www.frames.gov).