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Invasion by nonnative brook trout (Salvelinus fontinalis) often results in replacement of cutthroat trout (Oncorhynchus clarki) in the inland western United States, but the underlying mechanisms are not well understood. We conducted a four-year removal experiment to test for population-level mechanisms (i.e., changes in recruitment, survival, emigration, and immigration) promoting invasion success of brook trout and causing decline of native Colorado River cutthroat trout (O. c. pleuriticus). We chose 700–1200 m segments of four small mountain streams where brook trout had recently invaded cutthroat trout populations, two each at mid elevation (2500–2700 m) and high elevation (3150–3250 m), and annually removed...
Mortality of shadscale (Atriplex confertifolia [Torr. & Frem.] Wats.) was severe in Great Basin valley bottoms between 1983 and 1988. Puddle Valley, Utah, just west of the Great Salt Lake, typifies areas of extensive shrub loss in which density decreased from over to less than . We analyzed vegetation along a radial transect established in the bottom of Puddle Valley in 1987. Mortality was greatest at the lowest elevations where shrubs were initially most dense. These sites occurred where soil moisture, fine-textured soils, and bulk density were greatest of all sites evaluated. Soil was most saline at the margins of the valley bottom. Higher densities of live shadscale occurred where slopes are greater, soil is...