It happens every year at this time. At first it starts slowly: a branch or two, an isolated tree. And then, finally, swaths of color cover the landscape.
I’m talking, of course, about the leaves on the trees changing color—it’s something many not only look forward to, but plan entire weekends or even a vacation around. There is some predictability in terms of when the leaves change, but the peak can vary by up to 10 days.
Some years, the color is simply not as bright as others, but every year provides the opportunity to view wonderful fall colors. Color varies widely from location to location, and while the type of tree determines the color you will see, other factors—such as insects, the weather that has already occurred, and the upcoming weather—play a major role in how brilliant the colors will appear each year.
The drought is a major factor this year, but all may not be bad. One of the main purposes of a tree’s leaves is to manufacture sugars, and with the lack of rain in much of New England this spring, summer, and fall, those sugars are more concentrated. There are certain trees in which the concentration of sugar reacts to form a chemical called anthocyanins. Certain maples and oaks, as well as sumacs, produce the highest amount of anthocyanins, therefore displaying the most brilliant reds in the landscape. Of course, not all leaves are red in the fall—carotene and chlorophyll are also manufactured in the leaves during the growing season. The shorter days and cooler temperatures cause the chlorophyll to break down and disappear. Without the chlorophyll in the leaves, the remaining carotene causes the leaves to appear yellow.
Other factors to consider from the past year are the very mild December, which, in combination with the February cold snap and cold spring, damaged many flower buds on the trees. Did you notice there were little or no maple seeds (spinners) this year? The flowers of the maple trees, like the peach trees, were damaged. This means the energy of the tree was used in leaf production.
Of course, the lack of rain has caused some trees to already shed their leaves, or at least change color, but this has mostly occurring in urban areas. The forests of the Berkshires and northern New England still have less than 10 percent color change.
Gypsy moth defoliated the trees in some areas, so the new leaves that formed later in the summer likely won’t have as much color.
The best color occurs when the days are warm and sunny, the nights cool, but above freezing. With warmer-than-average weather predicted for the rest of the month and considering the other factors, this year’s color should be intense, but the leaves will likely fall somewhat faster than usual due to the stress of the drought.
Peak foliage season begins in northern New England in the final days of September and then typically spreads south to southern New England throughout October. Columbus Day weekend often has some of the best overall color a short drive from Boston. Last year’s warm fall delayed the color onset compared with previous years; I think this year will be similar.