PARENT SESSION
Poster Session 9: Arid Lands and Deserts
Tuesday, August 9, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Survivorship of woody plant seedlings under altered precipitation regimes is facilitated by a non-native, invasive grass.
Mason, Michael*,1, Weltzin, Jake2, Potts, Daniel1, English, Nathan1, Huxman, Travis1, Williams, David3, 1 University of Arizona, Tucson, AZ2 University of Tennessee, Knoxville, TN3 University of Wyoming, Laramie, WY
ABSTRACT- The encroachment of velvet mesquite (Prosopis velutina), a native, woody legume, and the spread of the non-native, warm-season bunchgrass, Lehmann lovegrass (Eragrostis lehmanniana Nees.), are two widely documented vegetation changes in the desert grasslands of southern Arizona. The extent to which precipitation variability interacts with the presence of native and non-native bunchgrasses to influence the recruitment of P. velutina is unknown. During August 2002, we planted scarified mesquite seeds in established, experimental, equal-density stands of native (Heteropogon contortus) or non-native (E. lehmanniana) warm-season bunchgrasses on the Santa Rita Experimental Range near Tucson, AZ. To simulate precipitation variability, bunchgrass treatments were assigned either a 50% increase or decrease from historic rainfall totals for the period of the North American Monsoon (July-September). Seedling emergence and 45-week seedling survival rates were influenced by an interaction between bunchgrass species and precipitation regime (Two-way ANOVA, F2,2= 4.13, p = 0.04; F2,2 = 14.72, p < 0.001 respectively). The positive effect of increased precipitation on seedling emergence and 45-week seedling survival was significant only in plots of the non-native bunchgrass, E. lehmanniana (Post-hoc pairwise T-test, T = -6.79, df = 4, p = 0.002; T = -12.36, df = 4, p = 0.0002 respectively). These results suggest that the spread of a non-native bunchgrass may interact with precipitation variability, two widespread aspects of global change in semi-arid regions, to facilitate the early establishment of a native woody plant.
Key words: rainfall manipulation, Eragrostis lehmanniana, Santa Rita Experimental Range, woody plant encroachment