PARENT SESSION
Contributed Oral Session 11: Invasive Species: Arid Lands
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 520 A, Level 5, Palais des congrès de Montréal

Global changes exacerbate threats from yellow starthistle (Centaurea solstitialis L.).

Dukes, Jeffrey^*,1, Loarie, Scott², Field, Christopher³, ¹ Department of Biology, Boston, MA, USA² Nicholas School of the Environment and Earth Sciences, Durham, NC, USA³ Department of Global Ecology, Stanford, CA, USA

ABSTRACT- Global environmental changes will alter interactions among plant species, sometimes favoring invasive weeds. We examined how multiple global changes affect the success of Centaurea solstitialis L. (yellow starthistle), often considered California's worst weed. We introduced seeds of this invasive species to the grassland plots of the Jasper Ridge Global Change Experiment, in the San Francisco Bay Area. Centaurea shoot biomass increased by over 600% in response to elevated CO₂, and by over 200% in response to increased nitrate deposition, but did not respond to modest warming, increased winter precipitation, or fire. Centaurea's unusually strong responses to CO₂ and nitrate far outpaced those of the resident plants in the community, suggesting that ongoing global changes will act to increase the weed's prevalence in western North America.

Key words: invasive species, carbon dioxide, community ecology, species interactions