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A central question of invasion biology is how an exotic species invades new habitats following its initial establishment. Three hypotheses to explain this expansion are: (1) the existence of ‘general purpose’ genotypes, (2) the in situ evolution of novel genotypes, and (3) the dispersal of existing specialized genotypes into habitats for which they are pre-adapted. Bromus tectorum is a selfing exotic winter annual grass that has achieved widespread dominance in semiarid western North America and that is actively invading salt desert habitats. We examined mechanisms driving this invasion in three complementary studies. In reciprocal seeding experiments with ten populations from saline playa, salt desert shrubland,...
Bromus tectorum is a dominant winter annual weed in cold deserts of western North America. We followed patterns of seed carry-over and abundance of the pathogen Pyrenophora semeniperda over 5 years at B. tectorum-dominated shadscale (Atriplex confertifolia) and sagebrush (Artemisia tridentata) sites in southern Idaho. We hypothesised that more seeds could potentially carry over at the drier shadscale site because of minimal autumn precipitation, but that P. semeniperda, a pathogen that primarily kills dormant seeds, would have more impact at the drier site, where a higher density of dormant seeds would likely be present in the early spring seedbank. Successful first-year seed carry-over was higher in years with...
Cheatgrass (Bromus tectorum L.) is a winter annual weed that presents a serious obstacle to rangeland restoration in the Intermountain West. The objective of this study was to evaluate factors regulating the size and persistence of cheatgrass carryover seed banks on semiarid sites in western Utah. We prevented current-year seed production in each of four habitats, then tallied emerging seedlings over the next 4 yr. Two iterations of the study were conducted during consecutive years. One year before initiation of each iteration, we estimated seed rain at each site. Above-average precipitation in 1998–1999 resulted in relatively high seed rain (13942 seeds·m−2) for the first iteration, whereas seed rain for the...
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Current invasion ecology theory predicts that disturbance will stimulate invasion by exotic plant species. Cheatgrass or Downy brome (Bromus tectorum) was surveyed in three sites near Florence, Colorado, U.S.A., immediately following Tamarisk or Saltcedar (Tamarix spp.) control and restoration activities that caused disturbance. Despite predictions to the contrary, neither mowing with heavy machinery nor tilling for seedbed preparation stimulated invasion, with a trend for the opposite pattern such that highest percent cover of B. tectorum was observed in the least disturbed transects. Aerial application of imazapyr for Tamarix spp. control caused mortality of nearly all B. tectorum and other understory plant species...
Rapid seedling growth and ability to compete against cheatgrass (Bromus tectorum L.) are 2 characteristics that perennial grasses must have for successful establishment on semiarid western rangelands. This study was conducted to determine the effects of temperature and competition from cheatgrass on seedling root and shoot growth of 'Hycrest' crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schult. � A. cristatum (L.) Gaert.] and 'Whitmar' bluebunch wheatgrass (Pseudoroegneria spicata (Pursh) L�ve]. For the temperature study, seedlings were grown in growth chambers with alternate 12-h day/night temperatures of 10/5, 15/5, and 20/5� C. Seedlings were destructively harvested on 6 dates and evaluated for 14...
Cheatgrass (Bromus tectorum L., Poaceae), an introduced winter annual, has invaded a variety of habitats in western North America. This study examines variation in cheatgrass germination response and after-ripening patterns that are related to differences in habitat and to yearly differences in weather conditions during seed maturation. Seeds collected from five contrasting populations in 1992 and 1993 were subjected to controlled dry storage and then incubated across a range of temperatures. Recently harvested seeds were dormant and germinated slowly, while fully after-ripened seeds were nondormant and germinated rapidly. The optimal incubation temperature for mean germination time shifted from 5:15 to 20:30 °C...
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We conducted a case studies testing effectiveness of a soil borne bacteria, Pseudomonas fluorescens strain D7, in controlling Bromus tectorum (cheatgrass) and in affecting the density of sown desirable seedlings. Response variables (foliar cover, aboveground biomass, and density of B. tectorum; density of sown native plants) were measured for three years after treatment.
    map background search result map search result map First-Year Responses of Cheatgrass Following Tamarix spp. Control and Restoration-Related Disturbances Weed-suppressive bacteria data set collected on Mid-Columbia National Wildlife Refuge Weed-suppressive bacteria data set collected on Mid-Columbia National Wildlife Refuge First-Year Responses of Cheatgrass Following Tamarix spp. Control and Restoration-Related Disturbances