PARENT SESSION
Poster Session 20: Invasive Species
Wednesday, August 10, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Contribution of deep soil moisture to infestation of disturbed sagebrush-steppe by exotic perennial forbs.
Horton, Jonathan*,1, Hill, Judson2, Germino, Matthew 2, 1 UNC-Asheville, Asheville, NC, USA2 Idaho State University, Pocatello, ID, USA
ABSTRACT- Semiarid lands in western North America are being invaded by persistent, introduced species that often cause undesirable alterations of ecosystem functions. Properties of invasive species alone are unlikely to explain invasiveness. Instead understanding how these properties match site conditions and differ from properties of established native species in ways that impart success to invaders is necessary. Resource partitioning of water by shallowly-rooted grasses and deeply-rooted sagebrush (Artemisia spp.) contributes to coexistence of these functional groups in undisturbed semi-arid ecosystems. Upon removal of sagebrush by disturbance, deep soil resources are available to other species, like exotic knapweeds (Centaurea spp.) and leafy spurge (Euphorbia esula), that are more deeply rooted than the remaining grasses. We hypothesize that access and uptake from deep soil water allows invasive forbs to maintain better water status resulting in higher gas exchange rates and a longer growing season that leading to greater reproductive output and competitive ability. We used stable isotope analysis to determine where functional types take up water in an area where sagebrush had been replaced by leafy spurge due to fire disturbance and an intact sagebrush system. We found that all species used water from shallow (< 30 cm) soil in June. Water uptake of grasses in August was still from the shallow soil, while sagebrush and spurge utilized water from deeper horizons. Sagebrush and spurge also had higher water potentials and less diurnal change in water potential than native grasses and forbs, suggesting that access to deeper soil allows for maintenance of favorable water status later into the growing season. These results indicate that fire may increase the susceptibility of sites to dominance by leafy spurge due to its ability to utilize water that is available deep soil horizons upon removal of sagebrush but is below grass rooting zones.
Key words: Sagebrush, Disturbance, Plant Water Source, Invasion