Soaked by sweat in the 90-degree heat of an Appalachian afternoon, Toby Obenauer disappeared into a massive tangle of kudzu that has laid siege to a hillside in the Cumberland Gap National Historic Park.

Carrying shears and a spray gun attached to a 40-pound tank of herbicide, his job is to stop the invading vines that threaten to turn several acres of the historic mountain pass into an impenetrable knot.

For Obenauer and other members of a National Park Service's Southeast Exotic Plant Management Team, today's enemy is kudzu. On other days, in other parks, they have been poked by the thorns of multiflora roses, tripped by Japanese honeysuckle and pinned in by melaleuca.

"It's not unusual to find yourself bleeding," Obenauer said. "You can get pretty banged up by the end of the day."

Wherever exotic weeds, shrubs and trees threaten to crowd out native plants in federal parks across the region, the six-member team is dispatched to engage in its own version of jungle warfare.

Modeled after hotshot crews used to fight wildfires, the Southeast team is one of 16 exotic plant management teams created over the past four years to fight invasive species that have infested an estimated 2.6 million acres in national parks.

"Our mission is to protect and restore natural areas and our natural heritage," said Linda Drees, chief of the National Park Service's invasive species branch in Fort Collins, Colo. "We want our visitors to see the native systems that are their heritage, not invasive species."

Nancy Fraley, an Asheville, N.C., botanist who leads the Southeast crew, said the exotic plants may not be as fast as fire, but they can be every bit as destructive to natural areas.

"Short of wildfire fighting, it is probably the next most physically taxing work that the park service has undertaken," Fraley said, her face reddened by the heat and the climb into Cumberland Gap. "It's very difficult work."

In protective clothing and safety glasses, and carrying either chain saws or heavy backpacks filled with herbicides, they comb fields and forests for invasive species.

Drees said the most troublesome exotic plants vary by ecosystem.

"A lot of these were introduced in this country in the late 1800s or early 1900s," she said. "They were planted in good faith, trying to improve a situation where they were looking at control for runoff or for ground cover."

In Appalachia, the teams target about 10 species that started harmlessly as lawn ornaments and got out of hand, taking ground once held by native plants.

Kudzu ranks at the top of the list.

Native to China, kudzu was introduced in the United States in the late 1800s as a climbing ornamental plant at upscale homes. In the 1930s, the U.S. Department of Agriculture decided kudzu could be used for erosion control and distributed 85 million kudzu seedlings in the South. The rest of the story is obvious.

Entire landscapes have been changed by the fast-growing vine. Trees, some 40 feet tall, have been completely engulfed in kudzu along the Cumberland River. Crews have prevented the plant from getting a hold that strong in the gap, but it is a constant battle, said Park Ranger Jennie Beeler.

In Florida's Everglades and surrounding areas, melaleuca trees, native to Australia, threaten to take over because they grow tightly together and crowd out other vegetation.

In many parts of the South, multiflora rose, an import from Asia, also is spreading into parks. Traditionally used to beautify lawns, the stubborn shrub, when planted in a line, has been used to form a kind of living fence to contain livestock.

Fraley said the multiflora rose, because of the sharp thorns, is one of the most painful to eradicate.

Sarah Cech of Marietta, Ohio, said she helped cut a tunnel through a huge plot of multiflora roses to reach and cut their trunks. "I still have scars from that," she said.

Cech said the work is physically exhausting, but it gets members of the team into some of the most beautiful places in the country, and they get to help keep them that way.

The National Park Service has developed field guides specifically for exotic plants growing within their boundaries. Many of the plants, Fraley said, have been around so long that people are surprised to learn that they came from another country.

"We'll never completely eliminate them," Fraley said. "But we are buying time for threatened native species."

Heather Bosserman of Fort Wayne, Ind., bottom, and Sarah Cech of Marietta, Ohio, spray a hillside in Cumberland Gap near Middlesboro, Ky. Patrick Campbell of Wilson, N.C., and Jason Wagner of Clive, Iowa, use all-terrain vehicles in their fight against kudzu in near Middlesboro, Ky.