Ring-necked pheasants and sharptail grouse gorge themselves year-round on the berries that Russian olives produce in groves all over Eastern Montana.

They love the nutrient-rich fruit that hang on branches even in the dead of winter. In extreme climates in the northeast part of the state, it has become a primary food source for some upland game birds, wildlife official say.

"When every other food source is under the snow, the Russian olive stands above it," said Ray Mule of Montana Fish, Wildlife and Parks.

But the non-native tree that grows thick in riparian areas and survives the harshest climates on the dry northern plains has its downside, too.

Cover and thermal protection that the trees offer some bird species also protect and camouflage predators hunting ducks in prairie potholes and at wildlife refuges on the upland plains, he said.

"It's a balancing act," Mule said. One the state has been asked to juggle.

A year ago this month, the Montana Native Plant Society and the Audubon Society petitioned the Montana Department of Agriculture to list Russian olive as a noxious weed. It noted that New Mexico, Colorado, Wyoming and several counties in Utah have already done so.

A decision - one that may placate those who love the tree and those who hate it - could be made by the end of the year, said Tonda Moon, a weed specialist with the Montana Department of Agriculture. In the year since the petition was filed, a new classification system has been developed. It includes a new category that accounts for beneficial uses of an invasive plant, such as Russian olive, as well as the practical aspects of managing it. Instead of eradication, which at this point probably isn't possible, the new category would prevent more from being planted.

"Yes, Russian olive is very much an invasive species, be we have to put it in perspective," Moon said. "We have to consider the environment and the financial costs."

Until recently, state and federal agencies recommended the tree for shelterbelts and distributed an average of 40,000 nursery stock plants a year, the petition said. Last year, the Department of Natural Resource Conservation nursery destroyed its stock of Russian olives.

At first blush, it may seem odd that the Audubon Society would want Russian olives listed as noxious weeds. But Janet Ellis, program director for the group, said that while the trees provide food and habitat for some birds, bird populations becomes less diverse as the invader replaces native vegetation.

"Grouse and pheasants eat Russian olives, but they use cottonwood, too," she said. "The native ecosystem is better for birds overall."

The petition refers to a Wyoming study that estimates 50,000 acres in Wyoming are covered with Russian olives. An estimated 10,000 acres along the Bighorn River are infested with it, the petition says. It noted that at least 19 Montana counties have reported Russian olive growth. They include Yellowstone, Carbon, Park, Treasure, Rosebud, Big Horn, Powder River and Custer counties in southern Montana and the Hi-line counties from Toole County to the North Dakota border.

"Although considered a desirable component of windbreaks in the semi-arid environments of Montana, it has spread from intentional plantings and invaded many riparian areas," the petition said.

The Audubon Society and the Montana Native Plant Society aren't alone in their concern. In June 2007, the Yellowstone River Conservation District issued a recommendation that new Russian olives not be planted in the Yellowstone River Valley and that where it's already established, "Russian olive should be controlled or eradicated."

Treasure County has designated Russian olives a noxious weed and has spent thousands to clear small areas of it.

Jennifer Cramer, Treasure County weed coordinator, said that along the Yellowstone, Russian olives have established "a pretty solid crown" along the river.

"We found it's a very expensive plant to get rid of," she said.

Chop it and burn it and new shoots emerge from the roots. Birds and wildlife that consume seed spread it. Seeds can float on water and ice for up to three days until they are deposited on a likely stream bank or wetland. They can lie dormant up to three years waiting for the right conditions to germinate.

Chopping trees down and treating the stumps with herbicide works. Trees can also be pulled out with a backhoe. Cleared areas have to be monitored to keep the trees from coming back, Cramer said.

"If large areas are cleared, you have to revegetate," Cramer said. "There would be a void and Mother Nature fills a void."

What Cramer has found in Treasure County is that newly cleared areas provide an excellent opportunity for other invasive plants.

"Where the Russian olives were taken out, we have a severe noxious weed problem," she said.

John Gaskin, a researcher at the Northern Plains Agricultural Research Station in Sidney, said the government is starting to think about Russian olives as an emerging problem.

"We usually see a lag between when they are introduced and when they go bad," he said of invasive species like Russian olive.

Research into biological control is just beginning he said. Scientists will be journeying to Europe and Asia, where Russian olives are native, to research environmental factors that keep the plants in check there, he said. They'll be looking for insects that are attracted to Russian olives and for any that survive only on Russian olive.

"Maybe they'll find something that just eats the seeds, so they don't spread," he said. "But biological control is still a long way off."

For Cramer, the easiest available solution is to purge the plants while they are young and small. It takes six to 10 years for the trees to mature enough to produce seed. The best way to control plants before they become fertile is to graze the area or keep it in hay, she said.

"One of the greatest methods of control is mowing," Cramer said.

Landowners might be more motivated to control Russian olives if they could find a way to make it pay, she said.

"I think it would be wonderful if someone could come up with a use for these trees," Cramer said. "It's a hard, weird wood."

Maybe it could be made into pellets and used as a renewable energy source, she suggested. Family members have used Russian olive logs in their wood stoves, Cramer said, and have been impressed with the heat it produces.

"They refer to it as an all-night log," she said. "It burns with a clear blue flame. But they do have to be careful with it because it burns hot."

Mack Cole, a Treasure County rancher battling an infestation of Russian olives on his property along the Yellowstone, said an artist friend has used it to carve decorative pieces.

"It's a pretty, stripy wood. I told him I could bring it up by the truckload," Cole laughed. "He said, 'No thanks.' "