When Vernon Cook sees wildflowers blooming near the historic entrance of Mammoth Cave, he feels a sense of accomplishment.
The Louisville, Ky., resident has helped foster the native blooms by removing invasive plant species from Mammoth Cave National Park, in Kentucky, and creating a place for the flowers to grow.
A Sierra Club volunteer, Cook routinely spends his vacations leading work crews at the park. The volunteers spend their days yanking tree of heaven and garlic mustard out of the ground. In the evening, they sit around a campfire and share stories.
"It's very rewarding to do this," he said. "You meet a bunch of great people."
Around the country, volunteers at parks and on trails are helping to address the problem of invasive species, and doing other trail maintenance, said Rich Dolesh, vice president for conservation and parks for the National Recreation and Park Association in Ashburn, Va. Often, they are motivated by a desire to restore the look and health of a landscape meaningful to them, he said.
"Many people see their sense of place being destroyed by aggressive, invasive plants," he said. "These are plants that will obliterate a landscape."
"People are willing to donate their time if they can see a meaningful improvement," he said.
Volunteers with the Sierra Club and other service organizations pay $200 to $2,000 to participate in the trips. They also must cover the cost of their travel to and from the work site. Accommodations range from tents to bunkhouses to lodges.
Susan Estes of Richmond, Calif., also leads work crews for the Sierra Club. She recalled returning to a spot in Arches National Park, in Moab, Utah, where she and a crew had removed a great deal of the invasive shrub tamarisk. A year later, many of the native plants that had been competing with the tamarisk for water were thriving -- including a cottonwood tree where a great horned owl was nesting.
"The beauty of seeing that ... people love the idea of doing something meaningful through their own personal efforts," she said.
Other volunteers sign up for work trips because they like to stay active on vacation or see an opportunity to learn more about a place, said Alex DeLucia, manager of the trails volunteer program for the Boston-based Appalachian Mountain Club. The club's volunteer programs often include tours by park rangers or area experts.
"You experience the place in a more meaningful way," DeLucia said. "That happens everywhere we go."
Cook volunteers because he wants to do more than vacation during his time away from work.
"Yes, I like to go outdoors. Yes, I like to camp. But for me, that in itself is not enough," he said. "Camping and hiking or even traveling are not an end in and of themselves. I look for opportunities to make a positive difference."
Kristine Martin volunteered to spend a week pulling hydrilla from a lake in the Ocala National Forest in Marion, Fla., because she wanted to learn more about the region. She enjoyed working with other volunteers and meeting locals. Rangers talked with the volunteers about the damage hydrilla does to the ecosystem, and shared details about forest wildlife. "It's an education," she said.
Interest in service trips is growing, DeLucia said. He attributes the increase to people having more time away from work due to the poor economy, and wanting to spend less money on pricey vacations. Many people also recognize that budget cuts have forced parks to reduce spending.
"We're able to provide a service with our volunteer program that (parks) simply wouldn't be able to address otherwise," he said.