Native plant communities are vital to a stable desert ecosystem. However, as fire frequency increases and timing of precipitation events change from historical patterns, native plant communities are being increasingly altered and outcompeted by invasive plants. These abiotic factors may favor invasive over native success thus altering existing native plant communities and changing the community dynamics between natives and invasives. We collected 240 soil cores from paired burn boundaries of five independent 2005 wildfires in the Beaver Dam Wash Nature Conservation Area in the fall of 2015. Each core had an assigned seed mix of invasive plants, native plants, or a combination of native and invasive plants. Each core was additionally assigned a fire treatment—unburned, burned, reburned—and a precipitation timing treatment in early December or early October for a full-factorial replicated common garden. After the following spring, the cores were harvested and the plants were sorted by species, measured, and weighed. Reproductive success was quantified by counting flowers and seeds produced by each plant.
Results/Conclusions
We found significant patterns in invasive plant success over natives across treatments. Invasives Erodium cicutarium, Schismus arabicus, and Bromus rubens all outcompeted native species when an early precipitation treatment was applied. This suggests that with early precipitation events, invasive plants can outcompete native species the following spring. In the case of invasive grasses B. rubens, and S. arabicus, all were more productive in density and biomass against native plants. Under reburn treatments, Bromus tectorum outcompeted native species. In some treatments E. cicutarium dominated all other species present. Our data indicates that across all treatments invasive plants are outcompeting native plants. With shifting precipitation events and changing fire regimes in the western deserts of North America, these abiotic events may be favoring invasive competition over native plant communities.