Annual wheatgrass (Eremopyrum triticeum) is an introduced, cool season, annual grass that recently established in disturbed areas of the Gardiner Basin in Yellowstone National Park (YNP). YNP managers are concerned that annual wheatgrass is preventing the reestablishment of native perennials in a disturbed area and has the potential to spread to other parts of YNP. Little is currently known about the reproductive capacity or spread of annual wheatgrass but it is suspected to be highly competitive with native species due to its winter annual lifecycle. Some studies predict that winter annual grass species will become more competitive with winter warming trends, while others report inconsistent responses to rising temperatures. The goal of this study was to assess the invasive potential of annual wheatgrass with two temperature treatments (ambient and elevated) in the field in Gardiner Basin using open-top chambers (OTCs). Lifecycle demographics were monitored in the treatments and used to parameterize a lifecycle model which was used to assess the population dynamics and invasion potential.
Results/Conclusions
We found evidence for a temperature treatment effect on annual wheatgrass seedbank density and population growth rates using the lifecycle model. Annual wheatgrass seedbank density is projected to increase by 44.61% by year 5 at elevated temperature conditions compared to 8.74% at ambient temperature conditions. Annual wheatgrass population growth is projected to increase more rapidly (mean annual growth rate, λ = 1.79) by year 5 at elevated temperature conditions than at ambient temperature conditions (mean annual growth rate, λ = 1.1). Projected population growth rates at elevated temperature conditions had 0.8 probability of being greater than rates of controls after 5 years of simulated dynamics and 0.5 probability of being greater than rates of controls after 10 years. Model simulated seedbank densities had 0.95 probability of being greater than densities under ambient conditions after 5 simulated years and 0.98 probability of being greater than densities under ambient conditions after 10 years. We found a negative relationship between annual wheatgrass percent cover and three of six neighboring plant species (R2=0.5288, p=0.002). Climate change projections for the region suggest warming winters may favor the winter annual wheatgrass. Prescribed burning may provide a management option.