Elevation competition between two invasive grass species (B. tectorum and B. rubens)

RM 217

Two species of grasses, Bromus tectorum (Cheatgrass) and Bromus madritensis rubens (Red Brome) are known for being widespread and invasive across the semiarid regions of western North America, including southern California. Both species grow quickly, have short life spans, and produce prolific amounts of seeds. Despite these similarities, these closely related grass species exhibit different, albeit overlapping, geographic distributions. In western North America, Cheatgrass tends to occur at higher elevations and more northerly latitudes whereas Red Brome lives at lower elevations and more southerly latitudes (both species are however, seen growing together at intermediate elevations.) It is assumed that these two species differ in their respective tolerances for cool and warm temperatures. It is also well known that climate change affects species distributions with different temperature tolerances and it is a possibility that with climate warming, Red Brome may begin to be more common at higher, cooler sites thereby adding to the invasive species load in these mountain ecosystems. The purpose of this research is to test the competitive abilities between the two grass species at different elevations, which involves a simple field experiment designed to test the competitive interactions between these closely related invasive grass species at a warmer low-elevation site near campus and a cooler high-elevation site in the nearby San Gabriel Mountains. Although data collection lasts from February to May, data analysis from Mid-March has suggested that plants at low elevation have overall higher canopy heights and higher germination rates than their high elevation counterparts.