- Associated Press - Thursday, October 6, 2011

Scientists seek to document later fall colors
DAVID SHARP,Associated Press David Sharp

PORTLAND, Maine (AP) — Clocks may not be the only thing falling back: That signature autumn change in leaf colors may be drifting further down the calendar.

Scientists don’t quite know if global warming is changing the signs of fall like it already has with an earlier-arriving spring. They’re turning their attention to fall foliage in hopes of determining whether climate change is leading to a later arrival of autumn’s golden, orange and red hues.

Studies in Europe and in Japan already indicate leaves are changing color and dropping later, so it stands to reason that it’s happening here as well, said Richard Primack, professor of biology at Boston University.

“The fall foliage is going to get pushed back,” Primack warned.

Down the road, scientists say there could be implications not just for ecology but for the economy if duller or delayed colors discourage leaf-peeping tourists.

Phenology is the study of timing in nature, whether it’s crocuses emerging in the spring, leaves falling from trees, or Canada geese heading south for the winter.

And it’s tricky business for fall foliage.

The budding of plants each spring is tied almost exclusively to warming temperatures, while fall’s changing colors are linked to cooling temperatures, decreasing sunlight and soil moisture.

The brilliant colors associated with fall happen when production of chlorophyll, the green pigment in plants that’s crucial to photosynthesis, slows down as the days get shorter and the nights grow longer. That exposes leaves’ yellow, red and orange pigments that are normally hidden from view.

How and when that happens depends on temperatures and moisture levels. In some years, the colors are more vibrant than others. Further complicating matters: A tree that’s stressed may simply drop its leaves, with no color change, or brown leaves.

“Fall is still an enigma,” said Jake Weltzin, executive director of the National Phenology Network in Arizona and an ecologist with the U.S. Geological Survey.

Scientists caution that heavy rain, drought-like conditions or temperature extremes can cause dramatic year-to-year fluctuations that don’t establish a long-term trend. For example, heavy rainfall in New England this spring, followed by a deluge caused by Irene, is causing fungal growth that’s causing some trees’ leaves to turn brown and drop earlier than normal.

William Ostrofsky, forest pathologist with the Maine Forest Service, is skeptical about whether there’s a proven link between fall foliage and climate change.

“I just don’t know that there’s any evidence to indicate there’s a trend one way or the other,” said Ostrofsky, who points out that year-to-year fluctuations make it difficult to discern long-term trends. “I really don’t think we’ve seen any long-term trend, as far as I can tell.”

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