It’s almost time for many residents and visitors to the Finger Lakes region to take their annual “Leaf Peeping” treks to the beautifully hued hills that rise from the lakes. Soon these hills will be ablaze with yellows, reds and oranges. Have you ever wondered why this phenomenon occurs and what determines which trees’ leaves will turn what color? Well, read on and I’ll explain it.
Nature equipped most broadleaf trees and shrubs with a defense mechanism to protect them from breaking under the added weight of snow falling and ice forming on the surface of their many leaves. These plants, called “deciduous” plants, lose their leaves and go dormant every fall. As a result, the surface available to snow and ice is reduced substantially. In the process of defoliating, the leaves undergo chemical transformations before falling to the ground.
As temperatures begin to cool and daylight hours get shorter, these conditions are nature’s signals to prepare for winter. First the plants go on a binge, producing food through photosynthesis to be stored in the roots to sustain the plant through the winter. When this is finished, the green chlorophyll drains from the leaves, revealing their true color – yellow.
Some leaves remain yellow while others turn orange or red. These colors are displayed when other chemicals are present. The presence of carotenoids gives leaves their yellow or orange color but aren’t seen during the growing season because of the chlorophyll. Carotenoids, which give carrots their orange color, are present to some extent in all leaves. The more carotenoid, the more intense the color.
Red leaves indicate the presence of anthocyanins, which are produced only in autumn. According to the International Society of Arboriculture (ISA), these complex, water soluble compounds in leaf cells react with excess, stored plant sugars and exposure to sunlight, creating vivid pink, red and purple leaves. A mixture of red anthocyanin pigment and yellow carotene often results in the bright orange color seen in some leaves. The photo provides an excellent example of brilliant orange color. It’s near the entrance to the Seneca Waterways Council Boy Scouts of America’s J. Warren Cutler Scout Reservation in the Bristol Hills near Naples.
Colors most affected by weather are the red tones created by anthocyanin. On warm sunny days, lots of sugar is produced in the leaves. Trees exposed to brighter sunlight generate the reaction between the anthocyanin and the excess sugar, creating the bright red hue. Cooler temperatures cause the veins in the leaves to gradually close, preventing the sugars from moving out, which preserves the red tones. Thus, a succession of warm sunny days and cool crisp nights can paint the most spectacular display of color.
As the trees’ show of color comes to an end, the buds for next year’s leaves, growing at the base of this year’s leaves, force the colorful leaves to disconnect and fall to the ground before the curtain of winter descends.