Pigments Make for Peak Foliage

When temperatures drop and days shorten, the local trees prepare for winter with brilliant displays. Not only is the fall foliage we witness each year a joyous marker of the seasons, but it also gives us a peek into the ecosystems that produce the famous Vermont vistas.

Pigmentation is the visual cue that signals the change and the process is relatively simple. When environmental clues indicate that winter is on its way, deciduous trees prepare by drawing energy-using cells inward. The process that produces fall colors is actually a fading of chlorophyll, which causes green pigmentation, to reveal myriad colors. As the cell responsible for photosynthesis, a decrease in daylight and therefore energy efficiency, prompts the tree to recall its chlorophyll from its outermost points. The retreat of the green pigment exposes the bright colors underneath.

Contrary to popular belief, most deciduous trees turn one color in the fall rather than follow a procession of yellow to orange to red. Their hue depends primarily on the dominant pigment the tree produces throughout the year. Carotene is the orange pigment that belongs to sugar maples while xanthophyll, the yellow pigment, characterizes American beech, green ash, paper birch, shagbark hickory, bigtooth and quaking aspens, and a handful of oaks.

The reds, purples, and even blues emerge from the production of anthocyanins in red maple, red oak, white oak, and staghorn sumac. While the vibrance of this pigment varies due to stressors such as nutrient deficiency and insect damage, anthocyanin is one of the few pigments that the tree produces in excess in the fall.

As trees slow nutrient transport systems in preparation for shedding their leaves, sugars become trapped within. The depth of color depends greatly on the weather conditions throughout the late summer. In ideal conditions, cold nights slow the movement of sugars and sunny, calm days prevent the leaves from dropping in one fell swoop.

An outlier in the Vermont woods is the Tamarack, also known as an eastern larch, and it is the only conifer that changes color this time of year. The needles turn a golden-yellow, but similar to oaks and beeches, they do not sever their connection to the branch completely. In the fall, the green, prickly undertones of other conifers create a striking contrast against the warm, smooth tones of the forests’ deciduous members. With some practice, you can learn to pick out different tree species in the fall by their color and shape from a distance, increasing the rewards of leaf peeping!

These brilliant fall color combinations act as a form of aerial communication between the trees and other ecosystem members. Not only will the color combinations indicate forest type to the human-eye—hardwood and oak-hickory forests holding the most spectacular combinations—but the changing colors also guide migratory birds along their routes. The language of the autumn forests tell us much that there is to know about our surrounding landscape.

By Claire E. Dumont

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