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.

Interference as a mechanism of invasion: The effect of 3 non-native Centaurea species on resource availability in a bunchgrass community.

Pankey, Joel^*,1, Black, R. Alan¹, ¹ Washington State University, Pullman, WA

ABSTRACT- The depletion of soil water was measured in three bunchgrass communities invaded by non-native Centaurea species. Comparisons were made in each community between pristine sites, sites invaded by Centaurea, and Centaurea-removal sites. This study was conducted in communities dominated by Festuca idahoensis, Pseudoroegneria spicatum, and Aristida longespica that are invaded by Centaurea maculosa, Centaurea diffusa, and Centaurea solstitialis respectively. Soil moisture was depleted where Centaurea occurred although results varied by site. When transpiration by Centaurea was temporarily eliminated, all sites experienced changes in soil water potential. Transpiration rates and pre-dawn leaf water potentials of the bunchgrasses were generally not changed. The soil at each site was between 50 and 75 cm deep. Consistent with previous studies addressing competition between Centaurea and grasses in soils of these depths, interspecific competition appears to be reduced through partitioning the soil volume. Centaurea species negatively affect the soil water status and may shorten the growing season for the native grasses by reducing the soil volume available to them.

KEY WORDS: competition, soil water, centaurea, invasion