Mapping Weeds & Resources:
A New Standardized System

by Carol Flaherty

1/97 BOZEMAN -- How much of a problem are noxious weeds? Ask any 10 professionals in the state and you will get agreement that weeds are a "big" problem. They'll tell you that when noxious rangeland weeds move into a Montana site, native birds and wildlife move out. When noxious weeds move into farm land, cost of food production increases.

But ask those same professionals just how many acres of Montana are infested with noxious weeds, and you might get eight or 10 different answers, says Diana Cooksey, land resources project coordinator at Montana State University.

Celestine Duncan, a private consultant with Weed Management Services in Helena, described the problem she found in some of her noxious weed surveys in the 1980s.

"In 1983, I did a weed survey in Montana," says Duncan, "and we came up with two million acres of spotted knapweed. We sent out a follow-up survey in 1988, and the total came back 4 million acres." In all probability, spotted knapweed infestations would not have doubled over those five years, says Duncan, which means that either the first survey was off, the second or both.

View a photo of spotted knapweed
northeast of Missoula

People were doing maps in many different ways, so discrepancies were inevitable, says Cooksey. When you think about mapping weeds, you can understand the problems.

A person takes a pencil and map and heads to the field. Stopping at known infestation sites and looking for new ones, the person marks the map, then goes back to an office to estimate the number of acres indicated.

"It's when you come back and start estimating acres that there's a lot of room for variation," says Cooksey.

For instance, even if a pencil started out making a sharp line, as the job wore it down, the thickness of its mark on a map would increase. Assuming the enclosed area was absolutely accurate, the width of the line itself might represent a 60-foot width of either rangeland or weed. Do you estimate based on inside the line or outside?

It is problems like these that led Cooksey and county, state, federal and university weed specialists to pool their perspectives and develop a standardized weed reporting system. All of the work was funded by the Montana Noxious Weed Trust Fund.

Though in its infancy, the "Montana Noxious Weed Survey and Mapping System" has the potential to tell Montanans not only what the problem is but also estimate rates at which various weeds are increasing. The system is compatible with computer "geographical information systems," but not limited to them, says Cooksey.

In fact, people with hand-made maps of their weeds can have GIS maps generated for them by Cooksey's office, if the maps are done following guidelines of the system. That service can be offered because of funding by the Noxious Weed Trust Fund. The data also then builds toward a comprehensive statewide map of weed problems.

"It will take a long time before we have a statewide weed inventory map," says Roger Sheley, MSU Extension Service rangeland weeds specialist. "We'll add to the data an acre at a time. At first, we'll get maps that are useful to an individual or the manager of a specific tract of land. Eventually, we'll be able to assess statewide management strategies."

Some individuals or land management agencies may start with a small project. Others are already going further, equipping themselves with GIS systems with the intention of mapping their entire county.

Madison County is going into GIS systems in a big way, says Dave Schulz, county weed supervisor. Both the weed office and the planning office will use a networked system to map subdivisions, weeds and other sites. The county committed funds, as did the Bureau of Land Management, and the Madison team also sought grants from a variety of outside sources.

"The map is something we can take back and use with individual landowners," says Schulz, who has trained at MSU twice for the upcoming GIS work. "I don't want this to sound bigger than it is," cautions Schulz, while adding the the full potential for the state to learn about its weed problems it enormous.

Valley County is well on its way to mapping the entire county using traditional hand-mapping methods, says Rick Stellflug, Valley County Weed Supervisor.

"We just keep plugging away at it. Whenever someone calls and we check out their report, we add it to a map.

They have submitted their maps to Cooksey to have entered into the computer mapping system, and will receive back a series of maps to work with.

"To take care of a problem, you have to know what is there. You have to have some idea of what it will cost. The only way to do that is to know what your weed inventory is," explains Stellflug.

Stellflug said leafy spurge is Valley County's largest noxious weed problem. He estimated that leafy spurge infests about 10,000 acres of Valley County's three million acres, Canada thistle infests another 6,000 acres.

But whatever the maps say, it still takes a knowledgeable interpretation of the maps to change data into information. For instance, Stellflug said he has mapped only 50 acres of Russian knapweed, but that the figure could be "way off" because areas along Fort Peck Reservoir have not been added to the map.

It also takes interpretation to know where to start on weed control, says Duncan.

"People tend to go to the worst infestation, and start controlling the weed there. They shouldn't start at the worst spot, which is often the center of a series of smaller infestations. Plot them, then work at the smaller infestations, gradually working toward the center of the sites. Put out the small ‘fires' first and then go to the main blaze," she recommends.

The strength of using the standardized mapping techniques agreed to by the state and federal agencies is so that information can be shared, says Cooksey.

"The data collected will be compatible with other people's data. . . and the computerized information should become more useful every year," she says.

Send questions or comments to Carol Flaherty, MSU Communications Services, Bozeman, MT 59717 or email to Flaherty and Cooksey at carolf@montana.edu. Visit the "Maps" web site.

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