Park Service officials are targeting hundreds of non-native plant species that have sunk roots in Yellowstone National Park.

Yellowstone officials released an environmental assessment that outlines bolstered efforts to eliminate invasive plants, seeds of which often are carried inadvertently into the park by its 3 million annual visitors.

Yellowstone biologists have identified 217 species of non-native plants inside the 2.2 million-acre park. That’s a 155 percent increase from the 85 species known in 1986. By comparison, Yellowstone has 1,350 known native species of plants.

Some invaders, such as spotted knapweed, oxeye daisy and dalmation toadflax, are widespread, said Warren Renkin, the park’s vegetation management supervisor. Others, he said, have been identified only in one or two locations.

“They’ve prioritized the species, so we’ve basically figured we’d get the most bang for our buck,” Renkin said.

The plan to fight invasives is two-pronged, Renkin said, relying on eradication and preventing entry.

“We’re going to see if we can really get a handle on the influx of weed seeds that’ll be coming in,” he said.

One idea is to wash construction equipment before it enters the park, Renkin said.

The other side of the invasive plant plan will focus on control, the park biologist said.

That effort will rely on chemicals, mowing and revegetation, he said.

More than 90 percent of Yellowstone is backcountry, so past treatments have mostly targeted areas near the park’s 467 miles of paved roads.

“More than 75 percent of our work is focused on front-country roads and developed areas,” Renkin said.

Non-natives have also treaded into the backcountry, however, the environmental plan said.

“In some places, Canada thistle has grown so dense it impedes off-trail travel in the front-country and the backcountry,” the document reads. “Non-native evergreen blackberry, which can easily reach over 5 feet in height and has been found in one location in the park, poses an even greater threat than Canada thistle for making off-trail travel cumbersome.”

Luckily — considering Yellowstone’s many blue-ribbon trout streams — no non-native aquatic plant species have been discovered, Renkin said.

The problem is complicated, Renkin said, by difficulties in monitoring and lack of funding.

“When it comes to the question of how effective we really are, we don’t have a whole lot of information,” he said. “The gut feeling is that we’re winning the war on some of the species, we’re treading water on others, and with some we’re winning a few battles but we’re losing the war.”

A lack of manpower and resources complicates matters, Renkin said.Seven full- and part-time employees are either partly or fully devoted to exotic plant management, he said. Another “12 to 15” summer seasonal employees split time between managing weeds and invasive aquatic invertebrate species, he said.