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.
Impacts of soil depth and competition with Centaurea solstitialis on Nassella pulchra.
Reever Morghan, Kimberly*,1, 1 University of California, Davis, Davis, CA
ABSTRACT- Many studies suggest that perennial grasses originally dominated California's Central Valley grasslands. Some stands of these native perennial grasses still exist, but they are often on rocky and shallow soils at the valley edges. There has been a great interest in reintroducing these native perennial grasses into restoration sites in the valley and in using them to control invasive species such as yellow starthistle (Centaurea solstitialis). However, few studies have looked at the effects of competition between C. solstitialis and these perennial grasses. In this study I planted seedlings of the native perennial grass purple needlegrass (Nassella pulchra) into 90 cm deep PVC tubes in the field. These tubes were either blocked or left open at the bottom to simulate shallow and deep soil. Competition was added to half of the tubes in the form of two Centaurea solstitialis plants. N. pulchra plants were grown for three years, and growth and reproduction were measured each spring. In the first year the growth and reproductive output of N. pulchra plants was negatively impacted by competition with C. solstitialis but not by soil depth. In the second and third years, however, both competition and soil depth had a negative impact on N. pulchra. In addition, most of the mortality of N. pulchra was seen for plants growing in shallow soils with competition. Shallow soils also negatively impacted the competitor. In all three years C. solstitialis in shallow tubes had lower growth and reproductive output than those in the deeper tubes. I conclude that restoration plantings of N. pulchra in areas with shallow soils and C. solstitialis may have high mortality, particularly if C. solstitialis is not controlled.
KEY WORDS: Nassella pulchra, Centaurea solstitialis, grassland restoration