Carotenoids and anthocyanins not doing their thing in leaves
November might also be warmer than normal across East Coast
Are the autumn leaves drifting by your window? Probably not.
All along the East Coast, from Maine to Virginia, it’s been a balmy fall, without the overnight crispiness that helps produce the panorama of golds and reds that’s typically sketched on many trees this time of year. Some spots, New York’s Central Park among them, are pretty much still seas of summer-like green. Or brown.
Boston was 7.4 degrees hotter than normal last month. Temperatures in Burlington, Vermont, were 10.5 degrees above the 30-year average. Central Park had its warmest October on record. It broke a mark set in 1947 with an average that was 7.2 degree Fahrenheit (4 Celsius) above normal, according to Jay Engle, a National Weather Service meteorologist in Upton, New York.
Thus the foliage situation. The force at play is a high pressure ridge over the northern Pacific Ocean that has been keeping the western U.S. cool while warming the east. And though the forecast says New York will get chilly this weekend, the East Coast overall stands a good chance of remaining toastier than usual all this month, according to the Climate Prediction Center in College Park, Maryland.
The trees are just following the rules. When the likes of an oak or a maple gets ready for winter, its chlorophyll production shuts down, robbing its leaves of their green tint. Then other chemicals, such as carotenoids and anthocyanins, are free to storm the stage with a display of yellows, oranges and reds.
Chlorophyll is the thing that allows trees to absorb light and turn it into sugar through the photosynthesis process. And there just haven’t been enough of the brisk nights that trap sugar in leaves and spur production of those other chemicals, according to Northeastern Area State and Private Forestry’s website.
“The warmer nights can certainly delay and even mute the change,” said Richard Harper, a professor in the Environmental Conservation department at the University of Massachusetts in Amherst. In other words, when they do show up, the colors won’t be as intense as during a brisk autumn season.
Of course, different species react to the weather in different ways, said Marlyse Duguid, a research scientist at the Yale School of Forestry and Environmental Studies in New Haven, Connecticut. “The introduced Norway Maple here in New Haven are all still dark green -- while most of our native Sugar Maples and Red Maples have dropped their leaves.”
At some point, most leaves will turn. A trip to New Hampshire or Massachusetts will still be worthwhile, Harper said. “A less than stellar fall in New England is still pretty stellar by most folks’ standards.”
— With assistance by Christine Buurma