Changing aspens mark first week of fall, but aspen show faces some trouble this year

The long, hot, seemingly endless summer of 2012 comes to an end Saturday, the day of the Autumnal Equinox when night and day are equally long.

Beginning Saturday, the nights are longer than the days for the first time since the Vernal Equinox in March. From now on, the cold bite of winter will likely be felt in the cold, darkening mornings, as shirts and shorts give way to coats and pants.

But the easiest way to know fall is here in the Eastern Sierra is the aspens. Most years, the high country is alive with blinding incandescent color: scarlet and tangerine and gold and crimson cascading down the mountains in sheets of living flame.

This year, though, is different.

Although the aspens are there—still aflame, still gorgeous—something has happened to dim their brilliance.

Driving toward Bridgeport, near the Conway Summit area you will see it—groves of aspens already devoid of their leaves weeks earlier than usual—without ever having turned to gold in the first place. Other groves—near Green Creek and Virginia Creek, near North Lake outside of Bishop—look lacy, like many of their leaves are missing or shrunk in size.

“There was a freeze in June that came just as the leaves were beginning to unfurl,” said Connie Millar, a Department of Agriculture paleoecologist who has spent many years studying trees and climate in the Eastern Sierra.

“That freeze killed many of the buds. They are very vulnerable at this time.”

Many other leaves, already more mature, turned black and curled around the edges, leaving the leaves in a kind of suspended animation where they never reached their fully mature size, she said.

The summer and fall has been windy, too, leaving some groves already leafless.

The result has been “reduced density” in many groves of aspens in the Eastern Sierra, like those beneath Dunderberg Peak (between Virginia Creek and Green Creek), where whole hillsides of aspens already look like the leafless groves of mid-winter.

To add insult to injury, the aspens also suffered another blow that might affect the color show this autumn.

“The dry winter meant some aspens didn’t get enough water for their leaves to develop their full sugar content,” Millar said. Leaves convert sunlight to sugars, which in turn nourish the tree, she said.

“There is still some confusion about the color changes of deciduous trees, but in the summer, trees absorb as much sunlight as they can and convert it to nutrients,” she said. “Day length triggers the sugars to begin to move back into the trunks and roots.”

When the green chlorophyll fades from the leaves, the colors left behind are the reds and yellows, she said.

It is possible the dry conditions this summer affected the trees’ overall health this summer, meaning the groves of aspens are less robust, which could also affect the overall density of the groves.

The good news is that the situation in the Eastern Sierra is due to specific events—in particular the June freeze—unlike the massive die-off of aspens in the Rocky Mountains, which is still poorly understood by scientists.

“This ‘Sudden Aspen Decline’ (SAD) has not been a problem for California,” Millar said. The SAD phenomenon has left large swaths of Colorado, Arizona and other Western states bereft of their aspen groves, and scientists are still unclear as to why, although some evidence points to climate change factors.

But California’s aspens are already more resilient to warming temperatures due to the state’s location.

“Our trees are already exposed to our Mediterranean climate (hot, dry summers and mild, wet winters) and that helps to insulate us, at least as of now,” she said.