jtm, tim, pdb

SOUTH LAKE TAHOE -- Warmer than normal temperatures in the high country hasn't stopped the onslaught of autumn, especially in Alpine County where bursts of bright yellow, orange and red aspen leaves from trees dot Highway 88.

The turning of the leaves is the annual process that begins when shorter days and colder temperatures signal trees that it's time to shut down.

If rain stays away, the colors should last two to three weeks, said June Leval, who works for the U.S. Forest Service in Markleeville.

The colors appear as the leaves gradually stop using sunlight and air to produce food for themselves, a process called photosynthesis. Less photosynthesis means less chlorophyll, a chemical which causes leaves to be green.

Colors begin to appear as the supply of chlorophyll dries up. Leaves turn their real colors, in a sense -- yellows and oranges. Reds and browns result from sugar or waste getting trapped in a leaf as it dies.

During winter, sugary food, or glucose, produced by a tree gets stored in its roots and limbs and acts as an antifreeze. It allows trees to keep from snapping in half in ice-cold, windy weather.

The aspens in Alpine Coounty are just starting the shutdown process. Aspens in the Lake Tahoe Basin are farther along.

"They are nowhere near full color, but a person wouldn't be disappointed," Leval said on Thursday looking out the window of her Markleeville office.

The Forest Service is in the process of counting how many aspen in the basin because they're being crowded out by white firs and Jeffrey pines.

"Aspens need full sunlight," said Dave Fournier, a Forest Service silviculturist. "They can't handle competition for light and eventually the conifers win out."

An aspen on average lives for 80 years. A few in the basin are about 120 years old, Fournier said. Aspens that grow west of the Mississippi River regenerate through root sprouting, not seeds. That's why aspen stands grow in clumps and only spread because of a natural event such as a landslide, Fournier said.

The Forest Service is also mapping aspens for a different reason: tree carvings. The Sierra Nevada for years was home to Basque shepherds, who would use idle time to carve their names and the date into the soft bark of the tree.

The Forest Service has a volunteer program called Passports in Time. Last spring, four volunteers accompanied John Maher, a heritage resource manager at the agency, to map the carvings on the East Shore south of Spooner Summit.

But not all aspen carvings found are old.

"Most aspen groves you'll find something like 'John loves Jane,'" Maher said.