The Splendor of Autumn
Every fall we enjoy the beauty of fall colors. The mixture of red, purple, orange and yellow is the result of a chemical reaction that occurs in the tree as it changes from summer to winter.
During the spring and summer the leaves act as factories where the nutrients necessary for the growth of the tree are produced. This process of making food takes place in the many cells in the leaf containing chlorophyll, which gives the leaf its green color. This unusual chemical absorbs energy from sunlight that is used to convert carbon dioxide and water into carbohydrates, such as sugars and starches.
Green pigments are accompanied by yellow to orange pigments, carotenes and xanthophyll pigments that give carrots their orange color, for example. Most of the year these colors are masked by large amounts of green.
Chlorophyll breaks down.
But in the fall, due to changes in daylight length and temperature changes, the leaves stop making food. Chlorophyll breaks down, green color disappears, and yellow to orange colors begin to appear and give the leaves their fall glory.
Other chemical changes may occur as well, creating additional color through the development of red anthocyanin pigments. Some compounds bring out the reddish and purplish colors of trees such as dogwood and sumac, while others give sugar maple its brilliant orange color.The autumn leaves of some trees show only yellow. Others, like many oaks, show mostly brown. All these colors are due to the mixing of different amounts of chlorophyll residues and other pigments in the leaves during autumn.
Other changes occur.
As autumn colors appear, other changes are taking place. At the point where the leaf stem attaches to the tree, a special layer of cells develops and gradually breaks down the tissue that supports the leaf. At the same time, the tree seals the cut, so that when the leaf is finally blown away by the wind or falls under its own weight, it leaves a scar behind the leaf.
Most broadleaf trees in the north shed their leaves in the fall. However, dead brown leaves on oaks and some other species may remain on the tree until regrowth begins in the spring. In the south, where winters are mild, some broadleaf trees are evergreen. That is, the leaves remain on the trees in winter and retain their green color.
Only a few trees lose their leaves.
Most conifers - pines, spruces, firs, hemlocks, cedars, etc. - are evergreen in both the north and south. The needle- or scale-like leaves remain green or evergreen year-round, and individual leaves may last two to four or more years.
Weather affects color intensity.
Temperature, light and water supply affect the degree and duration of color fading. Low temperatures above freezing will favor the formation of bright red-producing anthocyanins in maples. However, an early frost will weaken the brilliant red color. Rainy and/or cloudy days add to the intensity of fall colors. The best time to enjoy fall color is on a clear, dry and cool (not freezing) day.
Enjoy the color, it's only there for a short period each fall.
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