THE RUGGED LANDSCAPE OF THE DAKOTA PRAIRIE NATIONAL GRASSLAND stretches over 1.2 million acres in two states. These grasslands support a diversity of uses including livestock grazing, wildlife habitat, paleontological and archeological digs, oil and gas production, and recreation.
“The federal grassland boundaries you see on a map can be misleading,” explains Chad Prosser, Range & Weeds Program Manager for Dakota Prairie Grasslands. “Within our borders are significant portions of state and privately owned land that are permitted to ranchers for livestock grazing. That’s why developing and fostering partnerships is so critical to the success of our invasive plant management effort.”
The majority of weed management on the grasslands is conducted through agreements with either county weed control boards or grazing associations. “This allows us to leverage dollars with the partnerships and stretch our budget to get more work done on the ground,” says Prosser.
Invasive Plant Management
The invasive plant program is based on prevention, early detection, control, restoration and public education. Canada thistle (Cirsium arvense L.), leafy spurge (Euphorbia esula), absinth wormwood (Artemisia absinthium), black henbane (Hyoscyamus niger L.), and houndstongue (Cynoglossum officinale) are priority noxious weeds in the grasslands. Infestations are managed on a watershed scale across ownership boundaries starting at upper reaches of watershed and working downstream.
In 2014, about 22,000 acres of noxious weeds were treated; more than half of those acres were on leafy spurge in the Sheyenne Grasslands in eastern North Dakota. Although leafy spurge biological control agents are working well on some sites, infestations of spurge are expanding on sites where insect populations have declined. “The flea beetle (Aphthona spp.) populations cycle, and when their numbers are down we use herbicide applications to contain and control the weed,” explains Prosser.
Canada thistle and absinth wormwood are located throughout the Dakota Grasslands. Populations are controlled based on management goals and objectives. Milestone® herbicide applied at 5 to 7 fluid ounces per acre effectively controls both weeds.
Rocky mountain juniper (Juniperus scopulorum) and creeping juniper (J. horizontalis) are native plants that have been increasing on the grasslands the last 50 years.
“The mixed prairie grassland evolved with fire and grazing, but fire has been mostly removed from the equation,” says Jack Dahl, botanist with the Medora Ranger District. “This allowed the junipers to increase exponentially, especially on north facing slopes, on sites that should be dominated by grasses and forbs. Encroachment of junipers may be one of the biggest natural resource challenges we face in the grasslands without the use of prescribed fire.”
“The historical fire cycle was about every 15 to 25 years in the badlands,” Dahl explains. “Without fire, the junipers spread onto upland sites shading desirable grasses and reducing livestock carrying capacity.” In addition, to juniper encroachment, an increasing concern about the unchecked spread of exotic cool-season grasses such as Kentucky bluegrass, smooth brome grass and crested wheatgrass into native grasslands is becoming a focus of researchers and land managers.
Oil and Gas Development and Invasive Plants
Bakken Oil Field activity has increased disturbance and the risk of introducing new weeds to the Little Missouri River Grassland. Billings County Weed Control Board works with the oil companies and their private contractors to manage weeds on roadsides, drill pads and pipelines.
“One of our focus areas in public education is with the oil and gas companies,” says Katie Clyde, Supervisor for the Billing County Weed Control Board. “We are at the south end of the Bakken Oil Field, so any new roads, pipelines, or drill pads have to be inspected and approved by county zoning board.”
The weed district conducts a pre-inspection survey prior to any pipeline construction and monitors roadsides for newly invading weeds. If weeds are present the oil company has to control the infestation and continue monitoring.
Black henbane and absinth wormwood are big problems on disturbed areas, especially roadsides. Although gravel pits in Billings County are currently kept weed-seed free, some stockpiles were historically contaminated with these weeds and viable seeds are still present. “We hope within the next several years that all gravel pits in a three-county area will be certified weed-seed free,” says Clyde. “Until we have stockpiles that are free of noxious weed seed, our job will be more difficult.”
The Dakota Prairie Grasslands have a long history of restoration and that continues today. Disturbed sites are seeded as soon as possible to reduce weed invasion and erosion. Since the 1990s, managers have seeded a native mix that includes western wheatgrass (Pascopyrum smithii), green needlegrass (Nassella viridula), prairie sandreed (Calamovilfa longifolia) and Great Basin wildrye (Leymus cinereusis).
Partners agree that the most important asset to the invasive plant program is the ability to work together toward a common goal.
“You have to have a team approach—not only within an agency but also with outside partners. Sometimes you hit a bump in the road, but you have to keep moving forward as a team,” says Dahl.
Prosser agrees, “Partnerships allow us to have more eyes looking for invasive plants and that local on-ground knowledge is instrumental in the success of any management effort. Our weed crews and those of our partners are doing a great job, and we are extremely appreciative of the work they do.”
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