Submitted to: Weed Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/5/2004
Publication Date: 5/1/2005
Citation: Sheley, R.L., Jacobs, J.S., Svejcar, A.J. 2005. Integrating disturbance and colonization during rehabilitation of invasive plant dominated grasslands. Weed Science 53(3):307-314. Interpretive Summary: Disturbance creates safe sites for desired species germination and emergence, but is only useful where desired species are present to occupy newly available safe sites. In this study, we found that increasing intermediate wheatgrass seeding rate increased the likelihood that a seed would reach a safe site, especially where there was a disturbance prior to seeding. Spotted knapweed was generally lower where intermediate wheatgrass was highest. One approach to rehabilitating weed infested rangeland is to design disturbances that favor desired species and then use high seeding rates that overwhelm the pool of available seeds and occupy a high percentage of safe sites.
Technical Abstract: Our objective was to test portions of the theory of successional management, and to further our understanding of the relationship between disturbance and colonization during revegetation of invasive plant dominated grasslands. We hypothesized that 1) intermediate wheatgrass density and biomass would be greatest at highest seeding rates, 2) control and tillage procedures that increase the availability of safe sites would increase wheatgrass abundance, and 3) spotted knapweed density and biomass would be lowest in treatments yielding highest wheatgrass density and biomass. Treatments included three disturbance levels: 1) no disturbance, 2) application of the non-selective herbicide glyphosate ['(phosphonomethyl) glycine], and 3) tillage applied in the fall of 1995. The four colonization treatments were seeding intermediate wheatgrass at rates of 0, 500, 2,500, and 12,500 seeds m-2. Treatments were factorially applied in a randomized-complete-block design with 4 blocks (replications) at each of two sites located in south-central and western Montana. Density and biomass of intermediate wheatgrass and spotted knapweed were sampled at peak standing crop in 1997 and 2001. At both sites, seeding 2,500 or 12,500 seed m-2 increased wheatgrass density over that of the unseeded control in 1997. The highest seeding rate produced almost 3-times as many wheatgrass plants as seeding 2,500 seeds m-2 that year. By 2001, only the highest seeding produced wheatgrass densities greater than that of the control at Bozeman. Seeding rates higher than 500 seeds m-2 yielded greater wheatgrass biomass than the unseeded control with or without either tillage or glyphosate. At the highest seeding rate, tillage or glyphosate doubled intermediate wheatgrass compared to no disturbance. Spotted knapweed was generally lower where intermediate wheatgrass was density and biomass was highest. One approach to rehabilitation and restoration is to design disturbances that favor desired species and then use high seeding rates that overwhelm the pool of available propagules and occupy a high percentage of safe sites.