PARENT SESSION
Poster Session 7: Invasive Species.

Monday, August 2 Presentations from 5:00 PM to 6:30 PM, Exhibit Hall A 1.

Do resource pulses determine community invasibility? Water and cheatgrass in Great Basin sagebrush steppe.

Allcock, Kimberly^*,1, Lortie, Christopher¹, Nowak, Robert¹, ¹ University of Nevada, Reno, Reno, Nevada

ABSTRACT- Determining plant community susceptibility to invasion by novel species is a fundamental concern of ecology. Disturbance is commonly proposed to periodically release resources thereby facilitating invasion. However, natural pulsing of resources could create a similar effect. In the Great Basin of North America, large areas once dominated by perennial shrub-steppe have been invaded and drastically altered by the annual grass Bromus tectorum (cheatgrass). In this system water is strongly limiting, precipitation events vary widely in size and timing, and the precipitation regime may become more variable with global climate change. The relative abilities of plant species to respond to water pulses could determine community susceptibility to invasion under these conditions. Our study explores the effects of water pulsing on individual species responses, competitive interactions, and community invasibility. Our first experiment tests the response of two exotic and two native grass species (cheatgrass, Agropyron cristatum, Pseudoregneria spicata, and Elymus elymoides) to variation in pulse size and interpulse length. The second, a mesocosm study, tests the ability of synthetic native communities to resist invasion by cheatgrass when subjected to water pulsing. The third tests the invasibility of intact native communities in the field under experimental water pulsing regimes. Because of its rapid growth, plastic annual life history, and early phenology cheatgrass responds more opportunistically to water pulses than other species, but is sensitive to increasing interpulse length and decreasing total water. Precipitation events in spring or autumn could facilitate invasion if frequency of subsequent moisture was great enough.

Key words: resource pulsing, bromus tectorum, invasion, sagebrush steppe