Ecologically Based Integrated Weed Management to Restore Plant Diversity

Ecologically Based Integrated Weed Management to Restore Plant Diversity

Summary

Investigations continued into the use of ecological theory and the principals of succession in combination with on-ranch resources to restore native diversity to spotted knapweed infested rangeland. Invasive species management treatments were applied and ecosystem assessments were collected on two ranches in western Montana. Seventeen workshops and field tours addressing ecologically based invasive species management were conducted in 2004 to a total audience of about 350 landowners and managers. Research results were presented at three national and international professional conferences and published in the popular press, proceedings, and scientific journals. Research and educational programs will continue in 2005.

Objectives/Performance Targets

Objective 1) Integrate weed management strategies on spotted knapweed infested rangeland to address the three causes of succession based on site conditions, whole-ranch management objectives, and available ranch resources.
Objective 2) Conduct rangeland eco-assessments to determine the effects of ecologically based management on controlling spotted knapweed and restoring native plant communities.
Objective 3) Determine the economic implications of incorporating ecologically based weed management into ranching systems.
Objective 4) Conduct educational programs for ranchers and agency personnel on ecologically based whole ranch management and disseminate the results through field tours, the popular press, and the scientific literature.

Accomplishments/Milestones

Two sites in the Bitterroot Valley were established in June and July 2003 to study integration of sheep grazing and biological control insects to reduce the performance of spotted knapweed and provide a disturbance to open safe sites, and seeding with desirable species to increase their availability and occupy safe sites. Each site was divided into two whole plots for the biological control treatment. Three 4.5 by 4.5 meter grazing exclosures were constructed at random within each of the whole plots and used as a control to test the sheep grazing effect on plant community characteristics. Approximately 300 ewes with lambs grazed both sites in July. Three hundred adult Cyphocleonus achates, a biological control weevil for spotted knapweed, were released onto each site in late July. Native hay was cut in July, and seeds from native forb species were collected throughout the summer and fall. A native seed mix of grasses and forbs was purchased. The hay and seeds were applied as five seeding treatments inside and outside the grazing exclosures on 1 by 5 meter plots in the second week of November. Baseline data were collected at the time the exclosures were built, before treatments were applied. Density and cover by species were sampled from four randomly placed 0.2 by 0.5 meter frames inside and outside each exclosure. Sheep utilization of spotted knapweed was sampled by clipping all the plants within one 0.2 by 0.5 frame placed inside and outside each exclosure after the grazing treatment was applied.

On the ranch in the Yellowstone Valley, an 80-acre pasture infested with spotted knapweed was Sprayed in 1999 with 2,4-D to reduce spotted knapweed. Six 2m2 exclosures were constructed to measure the effects of grazing on the plant community. Cattle grazing was deferred for two years after the herbicide application to allow grass recovery. The pasture was grazed by 100 ewes with lambs to reduce reestablishment of spotted knapweed. In 2003, the pasture was first grazed be 150 cow-calf pairs in May until approximately 60% of the grass was utilized. This was followed by grazing by 50 ewes and their lambs. Predators were a problem and it was difficult to contain the sheep on the pasture. Six hundred Cyphocleonus achates weevils were released on the pasture in July. In addition, approximately 2,000 weevils were released on another spotted knapweed dominated pasture on the ranch.

In 2004, the grazing treatments on the two sites in the Bitterroot Valley were modified. Site 1 could not be grazed because the cooperator was denied access to water. Site 2 was grazed by 12 rams from July through October. Density and cover by species were sampled from one randomly placed 0.2 by 0.5 meter frame from each of the five seeding treatments inside and outside each exclosure at both sites. Sweep net sampling was used inside and outside each exclosure to estimate weevil establishment. Spotted knapweed plants were uprooted and the roots were searched for weevil larvae. At Site 2, sheep utilization of spotted knapweed and grass was sampled by clipping all the plants within one 0.2 by 0.5 frame placed inside and outside each exclosure. The number of spotted knapweed flower heads in each of the sample frames was also counted. Five soil samples were collected and pooled from inside and outside each of the exclosures, which will be used to measure nitrogen content, nitrogen mineralization, and the seed bank. Three hundred Cyphocleonus achates weevils were released on each site in early August. In November, three seeding treatments were established at both sites. They were 1) no seeding, 2) broadcasting bluebunch wheatgrass, annual sunflower, and blue flax at a rate of 30, 10, and 10 lbs/acre, respectively, 3) discing the soil to a depth of 5 cm and broadcasting bluebunch wheatgrass, annual sunflower, and blue flax at a rate of 30, 10 and 10 lbs/acre, respectively. The treatments were replicated three times in each of the biological control treatments at each site. Plot sizes are ½ acre.

The grazing treatments were continued on the Yellowstone River Valley Ranch project. An electric net fence was used to contain the sheep in the areas of the heaviest spotted knapweed infestation and to prevent predation of the sheep by foxes, coyotes, and wolves. Contained sheep grazing was also used on another pasture targeted for restoration. Utilization was sampled from 1 m2 frames. The electric fence was effective in containing the sheep and excluding all predators with the exception of one grizzly bear.

Impacts and Contributions/Outcomes

Results from this research and demonstration show how management actions affect disturbance, species availability, and species performance to change a plant community from being dominated by an invasive species to being dominated by desirable species. Understanding disturbance, availability, and performance helps landowners and managers design and predict the outcome in integrated weed management. In addition, this project shows how resources available on ranches can be used following ecological principals to manage invasive species and improve productivity. Examples of treatment effects are shown in Tables 1 and 2 and Figures 1 and 2 below from data collected or published during this project.

A number of educational programs and presentations were conducted in 2003. The establishment of the first study site in the Bitterroot Valley was coordinated with the annual sheep rendezvous of the Montana Wool Growers Association. A field tour was conducted to about 10 ranchers with an impact on about 100,000 acres that support about 20,000 sheep and goats. The tour described the objectives and methodology of the study. Two programs were presented, one to about 75 people in Missoula County, and one to about 50 people in Ravalli County, as part of a pesticide re-certification program that had an impact on several large ranching operations, many small landowners, and a number of commercial weed management companies (commercial applicators). The results of the sheep grazing study in the Yellowstone River Valley were presented at the annual meeting of the Society for Ecological Restoration in Austin, Texas, in November.

Seventeen workshops and field tours addressing ecologically based invasive species management were conducted in 2004 to a total audience of about 350 landowners and managers. Results of research associated with this project and ecologically based invasive species management were presented at the Society for Range Management annual meeting in Salt Lake City, UT, the Ecological Society of America annual meeting in Portland OR, and the International Society for Ecological Restoration annual meeting in Victoria, B.C., Canada.

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