PARENT SESSION
Poster Session # 15: Plant Ecology.
Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
The effects of invasive exotic annuals on the water relations and productivity of native endangered Eriastrum densifolium ssp. sanctorum (Polemoniaceae) shrubs.
Wendel, Heather*,1, Sandquist, Darren1, 1 California State University, Fullerton, CA
ABSTRACT- Flood control programs along the Santa Ana River prevent the natural removal of perennial shrubs and leaf litter which modify alluvial scrub habitat and reset community succession. The lack of periodic flooding and deposition of wind-blown soil particulates from adjacent mining industries create suitable soils for invasive exotic grasses and forbs. Eriastrum densifolium ssp. sanctorum is a California endangered subshrub restricted to alluvial communities immediately following sand deposition by floods. I hypothesize that competition with exotic annuals will decrease the amount of soil water available to the deep taproot of E. d. sanctorum and ultimately inhibit growth and productivity. I established three removal treatments (removal of other native shrubs only, removal of shrubs and annuals, no removal) within solitary E. d. sanctorum plots (N=9) and measured predawn water potential, transpiration, stomatal conductance and soil water content values. To assess productivity differences, I determined the leaf carbon and nitrogen isotopic ratios and followed growth and seed production for one season. Although trends suggest the release from competition increases water use (greater water potential and transpiration values for plots with shrubs and annuals removed), shoot growth, and results in higher seed counts, there were no significant differences found between treatments (p-value>0.05). Nutrient-level differences as determined by percent nitrogen in the leaves (p-value = 0.002), imply annuals may be altering the soil chemistry. While there is no evidence to support an effect of annuals on the water relations of E. d. sanctorum, compensation through increased leaf production or nutrient cycling may yield different results. Further experimentation is needed to test these hypotheses in years of non-drought and with larger sample sizes.
Key words: water relations, invasive annuals, endangered species, competition