WHAT MAKES GREAT BASIN SAGEBRUSH ECOSYSTEMS INVASIBLE BY BROMUS TECTORUM

摘要: Ecosystem susceptibility to invasion by nonnative species is poorly understood, but evidence increasing that spatial and temporal variability in resources has large-scale effects. We conducted a study Artemisia tridentata ecosystems at two Great Basin locations examining differences resource availability invasibility of Bromus tectorum over elevation gradients response direct interacting effects removal perennial herbaceous vegetation fire. monitored environmental conditions, soil variables, B. establishment reproduction years. Soil water (measured as the number days matric potential was .� 1.5 MPa) nitrate micromoles NO3 � sorbed resin capsules per day ground) decreased with decreasing elevation. Lower-elevation sites had greater annual than upper-elevation did. levels were highest all elevations when soils wettest; not more variable lower elevations. Removal perennials increased availability, burning without only minor low establishment, biomass, seed production on high-elevation mid-elevation site during cold, short, growing season probably due ecophysiological limitations resulting from cold temperatures. Establishment, best explained characteristics variation water. fire emergence survival, biomass three times following removal, six after burning, 10-30 burning. Our data indicate varies across appears be closely related temperature higher High average cover may increase either or intact native typically fire, limiting growth reproduction. Following fluctuations, lowest relatively high (i.e., ecological condition).