Document: DAN-3-40-10

Dynamics of exotic species and their establishment in the Pawnee National Grassland, CO USA.

BETZ, D.* and W.K.LAUENROTH

Colorado State Univerisity, Ft. Collins, CO 80523 USA ¹

Abstract:
We investigated the distribution of plant species to determine if the open steppe is susceptible to the invasion of exotic species from roadsides in the Pawnee National Grassland. Forty-five paired roadside and open steppe sites were surveyed. Few exotic species were found in the open steppe (0.42/3m²) while the roadsides contained significantly more (4.6/3m²). We also examined the soil seedbank along a transect from roadsides to 25 meters into the open steppe. We found that a greater number of seeds of exotic species were found in the roadsides ( 1,381 seeds per m²) versus the open steppe ( 158 seeds per m²), and fewer seeds of native species were found in the roadsides than the open steppe. To investigate why roadside exotic plant species have not encroached onto the native open steppe, we planted two exotic species: downy brome (Bromus tectorum) and Dalmation toadflax (Linaria dalmatica), into the open steppe. A matrix of 5 treatments were applied: 1) water additions; 2) nitrogen additions; 3) disturbance; 4) light cattle grazing; and 5) water plus nitrogen addition. Dalmation toadflax did not establish in the research plots although downy brome was successful in germinating and establishing. The nitrogen and nitrogen plus water treatments were the most successful in promoting the growth of downy brome. These results suggest that if seeds of exotic species become plentiful in the seedbank of the open steppe during wet years and over time if nitrogen deposition increases due to human sources, an aggressive exotic species invasion may occur in the Pawnee National Grassland.

Keywords: invasive species, weeds, grassland, establishment

This abstract is being presented at: 3:30 PM in session:
Poster Session #17: Vegetative Analysis.