why do the leaves change colour in autumn

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The Splendor of Autumn Every autumn we revel in the beauty of the fall colors. The mixture of red, purple, orange and yellow is the result of chemical processes that take place in the tree as the seasons change from summer to winter. During the spring and summer the leaves have served as factories where most of the foods necessary for the tree's growth are manufactured. This food-making process takes place in the leaf in numerous cells containing chlorophyll, which gives the leaf its green color. This extraordinary chemical absorbs from sunlight the energy that is used in transforming carbon dioxide and water to carbohydrates, such as sugars and starch. Along with the green pigment are yellow to orange pigments, carotenes and xanthophyll pigments which, for example, give the orange color to a carrot. Most of the year these colors are masked by great amounts of green coloring. Chlorophyll Breaks Down But in the fall, because of changes in the length of daylight and changes in temperature, the leaves stop their food-making process. The chlorophyll breaks down, the green color disappears, and the yellow to orange colors become visible and give the leaves part of their fall splendor.


At the same time other chemical changes may occur, which form additional colors through the development of red anthocyanin pigments. Some mixtures give rise to the reddish and purplish fall colors of trees such as dogwoods and sumacs, while others give the sugar maple its brilliant orange. The autumn foliage of some trees show only yellow colors. Others, like many oaks, display mostly browns. All these colors are due to the mixing of varying amounts of the chlorophyll residue and other pigments in the leaf during the fall season. Other Changes Take Place As the fall colors appear, other changes are taking place. At the point where the stem of the leaf is attached to the tree, a special layer of cells develops and gradually severs the tissues that support the leaf. At the same time, the tree seals the cut, so that when the leaf is finally blown off by the wind or falls from its own weight, it leaves behind a leaf scar. Most of the broad-leaved trees in the North shed their leaves in the fall. However, the dead brown leaves of the oaks and a few other species may stay on the tree until growth starts again in the spring. In the South, where the winters are mild, some of the broad-leaved trees are evergreen; that is, the leaves stay on the trees during winter and keep their green color.


Only Some Trees Lose Leaves Most of the conifers - pines, spruces, firs, hemlocks, cedars, etc. - are evergreen in both the North and South. The needle- or scale-like leaves remain green or greenish the year round, and individual leaves may stay on for two to four or more years. Weather Affects Color Intensity Temperature, light, and water supply have an influence on the degree and the duration of fall color. Low temperatures above freezing will favor anthocyanin formation producing bright reds in maples. However, early frost will weaken the brilliant red color. Rainy and/or overcast days tend to increase the intensity of fall colors. The best time to enjoy the autumn color would be on a clear, dry, and cool (not freezing) day. Enjoy the color, it only occurs for a brief period each fall. Text prepared by Carl E. Palm, Jr. Before we learn why leaves change color in, let's talk about what leaves do during the rest of the year. Each on a is like a tiny panel, gathering sunlight the tree uses to make food. Sunlight helps turn water and carbon dioxide into and, a that the tree uses for food (energy) to. This of converting water and carbon dioxide into and is called.


A called helps the of occur. is also what gives plants their green color. As begins, the days get shorter and shorter. With fewer daylight hours, leaves are not able to make as much as they can during the long daylight hours of spring and summer. As the fades, we are able to see other colors, such as orange and yellow,. Many people mistakenly believe that makes leaves change color. While this is not true, weather can affect how vibrantly the colors appear. If the weather is too hot or cold, the leaves will not be as bright as they begin to change. The best weather for foliage is sunny, warm days and cool nights. Water also plays an important in colors. If a tree doesn't receive water, the leaves will die faster and fall to the ground. If there is too much, the tree won't receive sunlight, and the leaves will not be brightly colored. You may be surprised to learn that each has small amounts of other colors in it year-round, even if we can't see them. During the spring and summer, overpowers the other colors, and all we see is green. With less to give the its green color, we begin to see the other colors, such as orange, yellow, and red, which have been there all along.

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