The Chihuahuan Desert has undergone dramatic shifts in vegetation structure and composition due to invasions of non-native plant species.  Our 20-year dataset has revealed a similar invasion of a winter annual plant community in the San Simon Valley of southeastern Arizona, where diversity and abundance of native annuals has drastically declined due to a sustained irruption of an exotic Eurasian species, Erodium cicutarium.  In conjunction with vegetation change, our study system is experiencing shifts in climate.  To fully understand the responses of the non-native and native plants to their environment, we followed germination throughout the growing season and implemented a growth chamber experiment.  We measured biomass allocation, growth rates, C:N ratios, and water-use efficiency of E. cicuatarium and several of the most dominant native plants across a gradient of temperature and water treatments.  Phenological shifts in these traits are determined by harvesting at various stages from growth to the reproductive phase.
Results/Conclusions

Preliminary results show that E. cicutarium germinates early in the season and across a wide range of environmental conditions.  Surprisingly, a native species, Astragalus nuttallianus, maintains similar abundance as E. cicutarium, while all other native species remain at low abundances throughout the growing season.  Although E. cicutarium displays higher biomass, A. nuttallianus suffers less mortality, perhaps demonstrating a heightened ability to withstand current drought conditions.  Supplementary growth chamber data also indicate that A. nuttallianus is able to maintain higher photosynthetic rates than E. cicutarium.  Preliminary results would indicate that E. cicutarium and A. nuttallianus have growth and resource use characteristics that allow them to dominate, even during stressful environmental conditions.  Our results to date demonstrate the dramatic impacts of the non-native invasive plant, E. cicutarium and the shifts in community composition during drought conditions.  Our growth chamber results will highlight the plant physiological characteristics that facilitate the dominance of E. cicutarium, while understanding the persistence of select native species.  Ultimately, our results may provide a better understanding of community shifts in diversity and composition as a result of changing climate in this arid ecosystem.