PARENT SESSION
Friday, August 11, 8:00-11:30 am
COS 115 - Shrub and woodland ecology
L-14, Lobby Level, Cook Convention Center
Presiders: K Haskins and S Saha

Exotic plant communities shift water-use timing in a shrub-steppe ecosystem.

Kulmatiski, Andrew^*,1, Beard, Karen¹, Stark, John², ¹ Utah State University, Logan, UT, USA² Utah State University, Logan, UT, USA

ABSTRACT- Semiarid areas in the US have realized some of the most extensive and persistent exotic plant invasions on earth. Exotics may succeed in arid regions by extracting soil water at different times or from different depths than native plants, but little data is available to test this hypothesis. Using estimates of root mass, gravimetric soil water, soil water potential, and stable isotope ratios in soil and plant tissues, we determined water-use patterns of native and exotic plant species in native- and exotic-dominated communities in Washington State, USA. Exotic and native communities both extracted 12 ± 2 cm of water from the top 120 cm of soil during the growing season. Exotic communities, however, shifted the timing of water use by extracting shallow (0-15 cm) soil water in May, before native plants were active, and by extracting deep (0-120 cm) soil water in July, after natives had undergone seasonal senescence. ¹⁸O values of water in exotic annuals (e.g., -11.8 ‰ for Bromus tectorum) were similar to ¹⁸O values of shallow soil water (e.g., -13.3 ‰ at -15 cm depths) suggesting that the transpiration by these species explained early season, shallow water use in exotic communities. ¹⁸O values of water in taprooted exotics (e.g., -17.4 ‰ for Centaurea diffusa ) were similar to ¹⁸O values of deep soil water (e.g., -18.4 ‰ at -120 cm depths) suggesting that transpiration by these species explained late season, deep water use. The combination of water-use patterns by winter-active annuals and taprooted perennials potentially explains how exotic communities resist establishment of native species. Early season irrigation or the transplanting of natives with established root systems may allow native plant restoration.

Key words: shrub-steppe, alternative state community, natural abundance stable isotope