Rachael Hamby, Jarrett Cellini, Rebecca Brown, Department of Biology, Eastern Washington University, Cheney WA
Invasive winter annual grasses (IWAGs) germinate in the fall and exploit spring soil moisture, replacing native species. The well-known IWAG, Bromus tectorum (cheatgrass), is limited by biological soil crust (biocrust) in arid ecosystems. However, it is not known how biocrust affects other IWAG species in less arid environments. In recent years, the less-studied IWAG, Ventenata dubia, has spread throughout semiarid areas in the Inland Northwest, causing detrimental impacts. Observations suggest that V. dubia persists in biocrust dominated areas with shallow, seasonally water-inundated soils. Our objective was to determine whether V. dubia is affected more by biotic interactions with biocrust, similar to B. tectorum, or by abiotic factors such as spring water depth. To test this, seven ~25 m transects were established in 2012 with ~four 1 m2 plots ranging from high to low V. dubia abundance. In each plot, percent cover of moss, lichen and all vascular plants, and IWAG stem counts were recorded in 2012, 2013, 2015, and 2016. In spring 2016, standing water and saturated ground percent covers, and maximum water depth were recorded in all plots. The effects of spring moisture and biocrust characteristics on V. dubia were analyzed using mixed effect models.
While spring moisture characteristics were positively associated with V. dubia cover, biocrust abundance had no relationship. Maximum plot standing water depth (p<0.0068), percent of the plot that was saturated (p <0 .1686), and percent of the plot that contained standing water (p < 0.1966) all showed positive relationships with V. dubia cover in all years sampled. These results suggest that V. dubia abundance is driven by the abiotic factor, spring moisture, rather than the biotic factor, biocrust. Effective management techniques for B. tectorum may not be as effective for V. dubia. Long-term monitoring of V. dubia and the climate factors that affect it will be necessary to understand the ecological factors driving this species.