Diffuse knapweed (Centaurea diffusa Lam.) seedling emergence and establishment in a Colorado grassland
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Knapweeds (Centaurea spp.) are damaging invaders of grasslands and other North American rangelands. A field study was conducted to determine conditions that promote diffuse knapweed (C. diffusa) emergence and establishment in a native Colorado grassland (North America). Knapweed was planted in native grassland under treatments with different opening sizes, levels of competition, knapweed seed burial and season of seeding. There was no effect of opening size where competing natives were alive, but knapweed emergence in 5- and 15-cm openings was higher than 0-cm openings where natives were killed. Reducing competition reduced fall diffuse knapweed emergence, but did not affect spring emergence. Seed burial increased knapweed emergence, but the effect varied by season. Although diffuse knapweed emergence reached 35%, only four plants survived from 3,600 seeds. This native grassland did not prevent knapweed emergence or establishment, but both were so low that rapid knapweed invasion is unlikely.
KeywordsEmergence Exotic plants Invasive plants Invasibility Noxious weeds Soil disturbance Openings
This research was funded by the Colorado Agricultural Experiment Station, Dr. Lee Sommers, Director, under an initiative for research on Invasive Plant Species on Public and Private Lands. The authors thank Drs. George Beck and Don Klein for their valuable input throughout this study, Dr. Steve Abt and Tom Brisbane (Colorado State University Engineering Research Center) for allowing access to the study area, and Drs. Bill Lauenroth, Maria Fernandez-Gimenez, the editor and anonymous reviewers for their helpful comments and suggestions.
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