PARENT SESSION
Poster Session #19: Invasive Species Ecology: Deserts and Rangelands.
Tuesday, August 6. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Seasonality of simulated rainfall influences the interaction between the invasive annual grass Bromus madritensis ssp. rubens and Mojave Desert perennials.

DeFalco, Lesley^*,1,2, Nowak, Robert², ¹ US Geological Survey, Las Vegas, NV² Program in Ecology, Evolution and Conservation Biology, Reno, NV

ABSTRACT- The abundance of annual plants in the Mojave Desert is closely tied to rainfall; the timing of rainfall is temporally variable and may influence the interactions between native and non-native plant species. We established a field experiment at the Nevada Test Site in the northern Mojave Desert to understand how the timing of simulated rainfall influenced the production of three native perennial species that had native and non-native annual plant neighbors. Differing densities of the invasive annual grass Bromus madritensis ssp. rubens were established around individuals of Larrea tridentata (evergreen shrub), Achnatherum hymenoides (early-season grass) and Pleuraphis rigida (late-season grass) and irrigated either in winter (November-January) or spring (February-April). Seeds collected from beneath nearby shrub canopies were also broadcast around native perennials to compare Bromus' effects to those of predominantly native annual species neighbors. Aboveground production for the three native perennial species was reduced when Bromus neighbors were established in winter. Production was not affected for perennials with Bromus neighbors established in spring or for those with mixed species neighbors established in either season. The decrease in perennial production was associated with rapid germination and growth of Bromus neighbors that were established in winter. The variable response of native and invasive annual species neighbors to precipitation, and the consequent responses of the native Mojave Desert perennials, demonstrates the complex seasonal dynamics associated with the invasion of this non-native annual grass.

KEY WORDS: Mojave Desert, invasive species, plant interactions