When Chip Davis walked through Yellowstone National Park two years ago, he not only was surprised at how nature had rebounded after the devastating forest fires, but also at how many man-made edifices remained in disrepair.

Davis, founder of Mannheim Steamroller, a new age and experimental musical group that focuses on nature-oriented music, decided to put together a national tour to raise money for the park. The performances feature Mannheim Steamroller -- Davis on synthesizer, Jackson Berkey on piano and Ron Cooly on keyboards -- and the Yellowstone Symphony, an 80-piece orchestra Davis assembles in each city.

"I've never done a cause-related kind of thing," says Davis. "I'm not a staunch environmentalist. I'm a composer. But I do love nature. So we worked out this thing. It's the very first time ever in the history of the Park Service that they have had anything like this. I am doing 20 concerts and my goal is to raise $1 million" of the $16 million needed to repair the park damage.

The program consists of a selection of classical pieces that incorporate nature, such as Respighi's "The Pines of Rome," Debussy's "Ballade," Vivaldi's "La Primavera" and Ferde Grofe's Grand Canyon Suite ("Cloud Burst"), as well as some of Davis's "Fresh Aire" compositions. Concurrently, there are slide projections of Yellowstone's most beautiful scenery, as photographed by the park's rangers.

"There are 700 slides," says Davis. "It's what I call 'A Walk Through Yellowstone.' I sequenced the pieces, like a film score, to the music. I keep the orchestra in sync with what is going on on the screens."

For the Grand Canyon Suite, an 80-foot lightning bolt strikes the stage. And for another piece, there is a tape of birds chirping. "And we've found, when we play outside, this triggers the real birds!" he says.

"The Music of Nature -- A Concert for Yellowstone" will be performed tonight and tomorrow night at Wolf Trap, beginning at 8:15. Tickets are $13 and $20 and available at TicketCenter or by calling 432-0200.