Colors of Autumn
Since we have been experiencing a moderate drought for several weeks, the last vestiges of autumn vegetation became crispy or droopy. Greenery became shades of browns and yellows, trees shrugged their leaves, as if hoping for relief from heaven. Some years, frequent rains dull fall colors, but this year it seems, we have received just the right amount of rain and cool weather behind it, so that we will have a nice flush of autumn colors in the next week to ten days.
Varied theories abound for predicting the patterns of fall colors yet no single, definitive answer to the broader question of why trees turn color satisfies the scientific mind. Much of our understanding is physiological and chemical in nature.
A major factor among a myriad of variables is the diminishing length of the autumn day, reducing sunlight-gathering, food-making chlorophyll. As its near magical processes slow to a halt, chlorophyll degrades, and yellow xanthophylls and orange beta-carotene, ever present, but hidden by the show of green, reveal themselves.
Anthocyanins, pigments in the red spectrum (including reds and purples) begin to dominate the leaf color, aided by the variables of moisture and temperature changes. Colors produced by these compounds give us the dull-reds and purples of dogwood leaves, the vivid red brilliance of sugar maples, the reds of persimmons, tupelos (or gum trees), sassafras and others, all vary depending upon pH in the leaf. Drab brown Ozark tree leaves simply may have little pigment compound in their decaying cell walls.
The recipe changes from year to year and species to species as the proportions of heat, cold, sunlight, clouds, and moisture shift with nature. This is convention wisdom. In the last 20 years an entirely new field of study—plant-animal interactions— hint of broader mechanisms, a more wholistic view, beyond mere physiology, that of co-evolutionary functions of colorful tree foliage. Fall colors are further integrated in nature, signaling to fruit-loving animals and insects that the fruits are ready for harvest perhaps aiding seed dispersal, or that there is nothing left to eat here, signaling it’s time to leave.
For us, too, it is a time for reflection and new beginnings, even as summer fades away. Fall fragrances evoke a longing to know when to be still to take-in the embroidery of the chromatic flush that will take us through winter’s dull tones. The season to enjoy the brilliant colors of autumn is upon us.