Wednesday, October 6, 2010

Aspens deliver right on schedule

Leaf displays depend on pigments, other factors


By KATHERINE WUTZ
Express Staff Writer

Aspen trees north of Ketchum signal the onset of fall with their gold leaves. Aspens generally turn a golden yellow in fall, a response to the decreased production of chlorophyll, letting pigments called carotenoids show through leaf cell membranes. Leaf displays should last for the next few weeks. Photo by Willy Cook

Driving from the south valley up into the Sawtooth National Forest is like driving through the entire fall season.

In Hailey and south of Ketchum, the predominant color is still green, with a few aspens just beginning to display their familiar fall gold. The trees on the streets of downtown Ketchum are starting to develop their fall displays, with red maples and a few oaks adding variety.

But by Warm Springs, Trail Creek and Galena Summit, fall is in full swing, with the aspens exploding into brilliant shades of gold and orange and ushering in the peak fall foliage season.

The degree and type of color displayed by the area's trees depends on a number of factors, said Deb Taylor, botanist with the Ketchum Ranger District. The late, wet spring the valley experienced might lead to a particularly good show this season, Taylor said.

"Aside from the moisture making leaves rot faster, low temperatures tend to bring out more colors," Taylor said. "But again, there's a lot of factors out there."

Leaf colors depend on three pigments, displayed in various amounts to change the shade. A pigment called chlorophyll gives leaves their typically green color. As the length of the days decreases and that of the nights increases, production of chlorophyll slows, allowing the color of the carotenoids to show through. Carotenoids are responsible for yellow, orange and brown colors—those displayed by Idaho's aspens.

Pigments called anthocyanins, the same pigments that give apples and strawberries their hues, normally produce red leaf shades, found in sugar maples and some oaks. These pigments are produced in the fall in response to the excess sugars trees store for the winter.

The foliage shows in this region, then, owe their color mostly to the carotenoids. Taylor said one factor that may change the shade or degree of brilliance of the autumn leaves is tree stress, caused by a fire or by natural predators.

Though Taylor declined to comment on whether the 2007 Castle Rock Fire near Ketchum is having an impact on this year's foliage, she did say that stresses such as fire could change the foliage for years following an event.

She said the foliage is expected to last several more weeks.

"A really heavy rain or snow could bring down the leaves," she said. "But most of the time, once they start to change, we have a good 30 days to see the color."

Taylor recommends that seekers of fall foliage head for the Boulder Mountains north of Ketchum, which she said is the location of one of the best aspen color changes in the area.

"Even right out Trail Creek is really beautiful," she said. "There's ample opportunity for people to get out."

Katherine Wutz: kwutz@mtexpress.com




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