LARAMIE, Wyo. -- John Korfmacher has hiked or skied into the Snowy Range backcountry once a week for the last seven years. He hasn't missed a date yet, even when holidays fall on his scheduled day.

In the winter, he drives a Sno-Cat, and he knows where he's going well enough that he can navigate the route even in a whiteout. The tank-like machine tops out at perhaps 12 miles an hour or so when going downhill, and it doesn't get real warm inside, but it can haul people and equipment across rugged terrain.

The Snowies, while a great place for hiking, camping, fishing, snow machining and skiing, are also a great place for collecting data about alpine ecosystems, which are sensitive to physical and chemical atmospheric change. The Glacier Lakes Ecosystem Experiments Site was established in 1987 through the U.S.

The Forest Service and scientists have been monitoring the area ever since.

"It's like a wilderness ecosystem," program manager Bob Musselman said of the Snowy Range site.

It's also not too hard to access the area year-round, even from Fort Collins, Colo., where the program headquarters are located.

They gather lots and lots of data, and any one piece may not mean much, but subtle changes over time and microscopic shifts in water or air composition are the signposts that signal the balance of forests and people and seasons.

A few weeks ago, while road crews were busy clearing drifts of snow for the summer, Musselman, Korfmacher, electrical engineer John Frank and entomologist John Popp loaded equipment for yet another snowy trek, which they complete every Tuesday without fail.

A number of different research projects are ongoing, with the Snowy Range site included in several national monitoring programs.

The Sno-Cat rumbled across rotting snow and its own worn tracks to the first stop, a small metal building in a clearing north of Wyoming Highway 130. A smattering of instruments poked out of the ground and dangled from towers rising from the shack.

Korfmacher and Musselman loosened a cable and let down one of the towers, which held a fist-sized filter that captures chemicals from the air flowing through it. Scientists change the filter once a week and send the old one to a laboratory in Oregon as part of the Clean Air Status and Trends Network. That program, operated through the Environmental Protection Agency, gathers information from 86 sites around the country -- all of them in rural areas or sensitive ecosystems -- about pollutants in the air.

Inside the shack, instruments store weather, radiation and ozone data.

Ozone that day was 53 parts per billion, typical for that time of year. At almost 52 degrees, the day was the warmest yet, in keeping with the spring weather already established in the Laramie Valley. Balmy air in the high mountains promised a change in seasons ahead, though snow on the ground, necessitating snowshoes, still suggested winter.

"We're looking at long-term trends in the deposition of chemicals," Musselman said. "We'd like to keep going to get a much longer record."

Farther up, another station captures precipitation, which is also analyzed for its chemical content as part of a complementary program called the National Atmospheric Deposition Program, which includes 250 sites around the country.

Korfmacher and Musselman hiked to the site, beside a glacial lake, and switched out a bucket as part of their once-a-week task.

"This can be done cheaply, rigorously, and give some valuable results," Korfmacher said.

A short hike away, Frank and Popp completed their respective monitoring chores.

Tucked into a grove of spruce trees, a 75-foot tower of scaffolding and stairs held still more equipment, this time measuring carbon dioxide and water in the air as part of a program called AmeriFlux.

Inside a small cabin still buried in snow, with piles now collapsing off the roof, Frank downloaded thousands of pieces of information from the previous week at the station.

AmeriFlux sites measure the carbon production and absorption in different types of ecosystems around the country. The Snowy Range site is set in a mixture of spruce and fir trees.

"The whole point of it is to measure just how much carbon dioxide the forest pulls out of the atmosphere and breathes in," Frank said. "It also measures how much water vapor leaves the forest and goes into the atmosphere."

Atop the tower, instruments measure the carbon dioxide and moisture level of the air that passes by. Wind gusts coming down to the forest below tend to have more carbon dioxide and be a drier and colder. Wind gusts rising from the forest are warmer, moister and have less carbon dioxide, which the trees use to grow.

By taking 20 measurements per second, compounding that information into half hours, and then graphing those numbers across days and months and years, Frank can draw a picture of the forest waking up for the summer, actively photosynthesizing during the day, and releasing carbon dioxide at night.

In mid-May, the forest was on the cusp of entering the summer growing season.

When the tower was built several years ago, scientists situated it in the midst of healthy stand of spruce trees. These days, the spruce beetle has entered the area and infected the surrounding trees, many of them several hundred years old.

Frank's data about carbon absorption reflects that change.

"We used to get some higher numbers. Now they're lower. At the same time, our trees are dying," he said. "This carbon sink might eventually go toward zero and it might go positive. It might no longer be a carbon sink anymore. It might be a carbon source because the trees will start to decay."

Entomologist John Popp was along to survey the beetle activity. He traveled a circuit of traps to see if any had emerged yet and gathered a few larvae on the way. He'll also set emergence cages to trap beetles as they're leaving the trees.

"We keep track of numbers and time of year," he said.

He put a chunk of bark and a pair of larvae in a plastic bag. Tiny white lumps wriggled blindly.

Indeed, it's the tiny things compounded by the hundreds of thousands -- a beetle the size of a grain of rice, a measurement of a gust of air, the chemicals in a drop of water -- that signal a dying forest or a shifting atmosphere.