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Must read: Fading fall foliage colors in New England blamed on climate change

EAST MONTPELIER, Vt. - Every fall, Marilyn Krom tries to make a trip to Vermont to see its famously beautiful fall foliage.

This year, she noticed something different about the autumn leaves.

'They're duller, not as sparkly, if you know what I mean,' Krom, 62, a registered nurse from Eastford, Conn., said during a recent visit. 'They're less vivid.'

Other 'leaf peepers' are noticing, too, and some believe climate change could be the reason.

Forested hillsides usually riotous with reds, oranges and yellows have shown their colors only grudgingly in recent years, with many trees going straight from the dull green of late summer to the rust-brown of late fall with barely a stop at a brighter hue.

'It's nothing like it used to be,' said University of Vermont plant biologist Tom Vogelmann, a Vermont native.

He says autumn has become too warm to elicit New England's richest colors.

According to the National Weather Service, temperatures in Burlington have run above the 30-year averages every September and October for the past four years, save for October 2004, when they were 0.2 degrees below average.

Warming climate affects trees in several ways.

Colors emerge on leaves in the fall, when the green chlorophyll that has dominated all spring and summer breaks down.

The process begins when shorter days signal leaves to form a layer at the base of their stems that cuts off the flow of water and nutrients. But in order to hasten the decline of chlorophyll, cold nights are needed.

In addition, warmer autumns and winters have been friendly to fungi that attack some trees, particularly the red and sugar maples that provide the most dazzling colors.

'The leaves fall off without ever becoming orange or yellow or red. They just go from green to brown,' said Barry Rock, a forestry professor at the University of New Hampshire.