Cheatgrass (Bromus tectorum) invasions have fundamentally changed the Great Basin Desert plant community by perpetuating an invasive grass fire cycle. Native plants struggle to recuperate post fire and have been regularly outcompeted by invasive annuals. As climate change driven precipitation regimes shift, and early fall rain events become more frequent, invasive annuals may be all the more favored over native species. However, these same precipitation patterns may enable native plants to effectively reestablish and compete with invasive annuals.
We collected 96 soil cores from an uninvaded, undisturbed sagebrush community in Rush Valley, Utah in the summer of 2016. The soil cores were planted in a replicated full-factorial common garden block design. Each core was assigned a separate seed mix of either native plants, invasive plants, a combination of invasives and natives, or a restoration seed mix commonly used in land restoration efforts. Additionally, each core was assigned a fire treatment, burned or unburned; and a precipitation timing treatment, early October for early treatment or early December for late treatment. All cores were harvested the following spring. Plants were sorted by species, measured, and weighed. Reproductive success was quantified by counting the flowers, fruits, and seeds produced.
Results/Conclusions
We found significant competitive success of invasive plants across all treatments. Bromus tectorum and Sisymbrium altissimum had a significant increase in density, height, biomass, and seed production in early precipitation treatment cores. B. tectorum and S. altissimum under an early precipitation treatment outcompeted small invasive forbs Ceratocephala testiculata and Alyssum alyssoides in the invasive seed mix. C. testiculata and A. alyssoides were more prolific under late precipitation treatments. S. altissimum had the greatest growth response to the early precipitation and burned fire treatments, whereas B. tectorum had the greatest response in an early precipitation and unburned fire treatment. When grown in an invasive seed mix, B. tectorum density numbers are reduced by half. Our data suggests that with increasing fire frequency and shifting precipitation events, both B. tectorum and S. altissimum will become more competitive with other invasive and native species, altering the Great Basin Desert plant community.