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Rocky Mountain Cheatgrass Management Project analyzes benefits of Plateau treatment

by Wyoming Livestock Roundup

In light of increasing concern over cheatgrass encroachment in more parts of the West, and the desire to know whether treating cheatgrass with herbicide is cost-effective, the Rocky Mountain Cheatgrass Management Project was established in 2007.
A collaborative effort between Colorado State University (CSU) and the University of Wyoming (UW), the project includes an interdisciplinary research team working on the ecology and management of cheatgrass, or downy brome.
The Rocky Mountain Cheatgrass Management Project (RMCMP) began with the Southeast Wyoming Cheatgrass Management Project in Laramie, a consortium of public land management agencies, weed and pest districts, UW and CSU.
“One of the main questions brought up was why areas treated with Plateau herbicide had good control for three years, only to see cheatgrass reinvasion after that,” says Marques Munis, a CSU PhD student now involved with RMCMP. “The other question was that, if we have to go back and apply Plateau every three years, does that provide enough future benefit to justify the cost of initial treatment?”
Munis says focus groups and pre-project surveys provided the team with a number of scenarios to plug into ecological and economic models to provide a base for what was analyzed in the field.
“The main framework puts management at the center,” he says. “We’re focusing on ecosystem processes, rather than in the past where we’d look at the landscape, see a weed and treat it. It was instant gratification, but several years down the road we found cheatgrass coming back, so we want to know what happens in ecosystem processes that allows for reinvasion.”
Munis says the researchers are taking a process-based approach, discussing timing and resource availability.
“Cheatgrass is an annual plant that can grow rapidly. It’s able to take advantage of any excess resources in a plant community to produce more biomass,” he explains. “When there’s a lot of competition there aren’t as many resources in the soil, so there’s not as much chance for cheatgrass to grow.”
Munis says the research looks at what types of sites have higher resource availability.
“Growing season precipitation favors perennial grass cover. When perennial grasses are growing they can use those resources, but when we have dormant season precipitation those plants aren’t growing, but cheatgrass is, so it can use those excess resources to increase biomass,” he says.
He adds that the research has found cheatgrass to be a problem on south-facing sites.
“There’s less organic matter in the soil on south-facing sites, and a shorter amount of time that resources are available from the dry, coarse-textured soils, which tends to favor cheatgrass,” he says.
Disturbances to the plant community also contribute to negative feedback in perennial grass cover.
“With something like fire or a Plateau application we’re inhibiting the ability of the plant community to uptake resources, so there’s more opportunity for a fast-growing plant to gain,” he notes.
Field research asks in what part of the landscape is cheatgrass becoming a persistent problem, and in the sites persistently infested, is nitrogen availability one of the reasons for cheatgrass remaining on the sites? Also, the research asks what Plateau is doing to promote a perennial plant community.
For the research, eight pastures were chosen in three main areas – the Richeau Hills between Laramie and Wheatland, a site near Poll Mountain and another west of Laramie. All the sites were burned or unburned big sagebrush rangeland, and Munis says the burns were intentionally structured and occurred over a range of years, from a year or two before the study to 12 years before.
“When we look at south-facing versus north-facing sites, we see cheatgrass isn’t much of a problem on north-facing sites, whether they were new or old burned sites. On south facing sites we see persistent infestation of cheatgrass,” says Munis. “On unburned sites cheatgrass is a very small portion of the plant community, but when you look at new burned sites, with higher resource availability, cheatgrass is a significant portion of the plant community, and remains a significant portion in older burns, as well.”
“When we look at cheatgrass sites, the worst of the worst are hot, dry south-facing sites with coarse-textured soils with low organic matter,” he explains. “Sites with the opposite qualities don’t have as high of resource availability.”
Munis says that means land managers should target a more tightly-coupled system with less excess plant nutrients and water left over from the desirable plant community.
“There’s some tipping point where we have resources that are available in excess of what the perennial plant community requires to grow, and they’re able to be captured and turned into biomass by cheatgrass,” he says. “In north-facing sites with higher organic matter and higher biomass, more nitrogen and carbon is being sequestered in the biomass of the plant and isn’t available for cheatgrass to take advantage of, and that’s where we’re tipping the balance in terms of the perennial plant community over cheatgrass.”
The field data collected from the eight pasture studies has gone into parameterizing some ecosystem models to look at trade-offs. Following the ecological model an economic model comes into play, looking at the trade-offs between the cost of Plateau application and forage production, in terms of pounds of gain in a stocker operation.
“The main relationship we’re looking to tease out is whether spraying for cheatgrass is paying off in terms of animal performance and increased range productivity in the future,” he says.
Munis expects the bioeconomic model will eventually develop optimal management strategies between stocking rates and herbicide applications and maximizing the benefit expected from the different treatments.
He adds that the researchers would like to scale up from a pasture to a whole-ranch scale, and also expand the model to other areas, such as the Great Basin and southern Idaho.
“Expansion of what we’re looking at now is one of our goals for the future,” he says.
CSU PhD student Marques Munis presented his findings as part of the Rocky Mountain Cheatgrass Management Project at the January 2011 Wyoming Weed Management meeting in Casper. Christy Martinez is managing editor of the Wyoming Livestock Roundup and can be reached at

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