Donnie Nichols
County Reporter
As daylight shortens and temperatures drop, nature is about to change our forests into a magnificent, multicolor landscape. A sea of green will be transformed to yellows, oranges, reds, purples and all hues in between. Leaves are beginning to change colors. The leaves have actually been preparing for autumn since they started growing in spring.
In spring and summer, leaves are photosynthesizing, getting energy from the sun. There are two small tube-like structures: the xylem transports water and water soluble nutrients up to the leaves and the phloem distributes sugars and nutrients down to the roots of the tree. At the base of each leaf there are abscission cells through which these tubes pass. Photosynthesis produces chlorophyll in the leaf and gives it its green color. Carotenoids which produce yellow and orange colors, are also present throughout the year but are masked by the green of the chlorophyll. In fall, the abscission cells begin to swell and form a cork-like material, reducing and finally cutting off the flow of xylem and phloem between leaf and tree. Glucose and waste products are trapped within the leaf. Without fresh water to renew it, the chlorophyll begins to disappear. As the chlorophyll dissipates, the pigments produced by carotenoids start to show through.
The reds and purples, the result of anthocyanin, are not present year round but are actively produced toward the end of summer. Their formation depends on the breakdown of sugars in the presence of bright light as the level of phosphate in the leaf is reduced. When autumn days are bright and cool, and nights are chilly but not freezing, the brightest coloration develops.
As fall progresses, abscission (derived from the Latin root word for scissors - “to make a cut”) cells continue to swell and elongate and bit by bit push the leaf away from the stem ultimately severing the leaf from the tree.
The cold dry winds of fall strip trees of moisture though their leaves. By losing its leaves, the tree can conserve moisture in the trunk and branches to prevent drying out and dying. In addition, loss of leaves helps put the tree into a state of dormancy, greatly reducing the amount of energy needed to stay alive.
Some oaks, noticeably pin oaks, retain leaves until spring. Leaves that remain on trees during the fall and winter don’t retain their colors for very long. Like chlorophyll, pigments eventually break down and disappear. The only pigments remaining are tannins which are brown.
Come spring, the trees begin to bud. Leaf production is renewed and the cycle is repeated.
”The landscape of any farm is the owner’s portrait of himself.” -Aldo Leopold
