September Drought Could Spur Fine Fall Foliage

The dry spell this September in much of New England and the mid Atlantic could have an pleasant and surprising consequence, according to the Philadelphia Inquirer: great autumn color in the region's forests. The equation that makes leaves change color, and governs the intensity of their hue, is complex. If the nights are cool enough, or the wind blows too hard at the wrong moment, and the fall is spoiled. But we're off to a good start, according to the experts interviewed by the Inquirer.

At this time of year, plants slow down production of chlorophyll, the pigment that gives leaves their green color and helps them transform sunlight into energy. During the spring and summer, it masks other pigments in the leaves, and as the summer light wanes, so does the green. Trees stressed by drought can produce additional anthocyanin, the rich red pigment that characterizes sugar maples and other crimson fall trees. Because the change in fall color is so dependent on environmental and weather conditions, some scientists have thought to look to the annual event as a marker of climate change.

Some observers, such as those at the Mohonk Preserve in New Paltz, N.Y., have noticed the leaves changing colors later -- about a week on average -- than a century ago. It's an observation consistent with other changes -- an expanded growing season, earlier blooming of certain flowers and migration of certain birds, for instance -- that seem consistent with the temperature increase over the past century. But, as leaf-peepers know, identifying the peak of the fall foliage season is subjective, making it a difficult marker to pin down in connection with global warming.

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