Autumn is the great season of change in Massachusetts - from shorts to jeans, sunflowers to asters, hotel rooms to classrooms, and watermelons to apples. The changing temperatures and shorter days dictate changes to all species, and if you are a tree lover then fall is your Super Bowl! But what happens to trees in the fall and why do their leaves change colors?
The chemical in the cells of leaves which gives them their green hue is called chlorophyll. This chemical absorbs energy from sunlight that is used in the process to change carbon dioxide and water into food (sugars & starches) during the warmer seasons. When cooler temperatures and shorter amounts of daylight signal the end of these ideal growing conditions, the trees react by suspending photosynthesis which begins to dissolve the chlorophyll in the leaves. That allows various underlying pigments to show through, or mix in with the green hue of chlorophyll, to produce a dizzying array of colors each year.
Xanthophyll is responsible for the yellows commonly observed in birch, ash, and lindens, while carotene allows sugar maples and some species of Japanese maples to contrast exceptionally dazzling oranges against a dull autumn sky. Anthocyanin is the kindling which lights the burning red fire observed in the canopies of red maples, scarlet oaks, and sourwoods. Mixing of these hues can create the deep burgundy-purple found in flowering dogwoods and sumac, while also turning white oak foliage a dull brown like the paintbrush of a kindergartener who uses every color all at once.
Temperature, light, and water all have an influence on the intensity and duration of foliage colors. Rainy, overcast days tend to increase the brilliance, while an early frost can cause some of the first turning red maples to quickly lose their luster. The best circumstances for color is a dry end to summer leading into bright, sunny days in autumn ending with cool nights.
Whatever the circumstance year to year, fall is always a special treat in New England! Enjoy!
