Establishing native plants in crested wheatgrass stands using successional management Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/gt54kq84h

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  • Crested wheatgrass (Agropyron cristatum (L.) Gaertn.) is a nonindigenous perennial grass that was introduced to North America to improve the condition of degraded rangelands. It has proven to be a successful revegetation species due to its superior ease of establishment, strong competitive ability, and ability to tolerate grazing. However, crested wheatgrass is criticized for its ability to form monotypic stands that result in low plant diversity. The main objective of this study was to determine the effect of crested wheatgrass control methods on native plant establishment using a successional-based approach. I also looked at the effects crested wheatgrass control methods and revegetation had on crested wheatgrass and cheatgrass density and cover, and on soil nitrate, ammonium and water contents. I hypothesized that control methodologies and revegetation would decrease crested wheatgrass density and cover, increase the presence of native species, increase cheatgrass and annual forb density and cover, and initially increase soil nitrate, ammonium and water contents. In 2005, at one site in southeastern Oregon, 10 hectares of an established crested wheatgrass stand was treated with two control methods at two intensities: partial mechanical control (once disked), full mechanical control (twice disked), partial herbicide control (1/4 recommended rate of glyphosate), full herbicide control (full recommended rate of glyphosate), and an undisturbed control. In October 2005, one half of each plot was seeded with 10 native species, representing three different functional groups. These same procedures were repeated again in 2006. In June of 2006 and 2007, the density and cover of crested wheatgrass, cheatgrass, seeded species, and any weedy species phenologically competitive with the seeded species was sampled. In the first year the density of seeded species was: 30.1 plants m-2 in the partial mechanical control treatment; 43.9 plants m-2 in the full mechanical control treatment; 21.0 plants m-2 in the partial chemical control treatment; 22.0 plants m-2 in the full chemical control treatment; and 18.2 plants m-2 in the undisturbed treatment. By the second year all treatments were similar in seeded species density to the undisturbed treatment at 18.2 plants m-2, suggesting that control strategies did not increase the density of seeded species. Crested wheatgrass density increased and cover increased with the control treatments. Cheatgrass and the annual forb alyssum (Alyssum alyssoides (L.)) increased in density and decreased in cover with the control treatments. Soil ammonium concentrations and water content increased the first year following control treatments and decreased in the second year. Soil nitrate concentrations increased the second year following control treatments. I believe that by using a successional approach to management, land managers can direct plant community dynamics to increase the establishment of native species and meet resource agency goals.
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