PARENT SESSION
Oral Session #51: Invasions: Population and community interactions.
Presiding: T. Stohlgren
Wednesday, August 7. 8:00 AM to 11:30 AM. Graham Meeting Room, TCC.

Complex effects of multiple global change factors on plant invasions in experimental grassland plots.

Howe, Katherine^*,1, Ogba, Ndiya², Naeem, Shahid¹, Knops, Johannes³, Reich, Peter⁴, Tilman, David⁴, ¹ University of Washington, Seattle, WA² Benedict College, Columbia, SC³ University of Nebraska, Lincoln, NE⁴ University of Minnesota, St. Paul, MN

ABSTRACT- Biological invasions are one of the major threats to native biodiversity and ecosystem function in terrestrial ecosystems. Several studies have shown that, individually, increasing atmospheric CO₂, nitrogen deposition, and loss of biodiversity improve invasion success by exotic species, however it is unclear whether these three elements of global change will have interactive effects on biological invasions. We simultaneously manipulated atmospheric carbon dioxide, nitrogen deposition, and species richness in experimental grassland plots to determine the effects of altering these co-occurring factors on invasion success of two weed species, Crepis tectorum and Conyza canadensis. We found that the two species responded differently to experimental treatments. Cr. tectorum biomass decreased significantly under enhanced CO₂, whereas Co. canadensis under enhanced CO₂ and N conditions showed a dramatic increase in biomass as compared to Co. canadensis growing in ambient conditions. Assessment of the effects of individual resident species on the invaders showed that different native species had significant effects on the biomass of Cr. tectorum and Co. canadensis. These results suggest that various elements of global change may have unique effects on invasive species with different life histories, phenologies, and places of origin.

KEY WORDS: invasion, global change, biodiversity, CO₂