Why does leaves change color in fall

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. Most of the conifers - pines, spruces, firs, hemlocks, cedars, etc. 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. 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. The best time to enjoy the autumn color would be on a clear, dry, and cool not freezing day.

Apply Give Partner. Gateways for Advanced Directory. Ah, autumn—the air is crisper and the trees are turning brilliant shades of gold , red, and brown. In the temperate areas of the world, it gets very cold in the winter and there is not much sunlight, which the trees need to feed themselves. This preparation process is what causes the leaves to display their striking autumn colors. In the summer , most trees have green leaves because they contain the pigment chlorophyll. This pigment is also used to convert sunlight into energy for the tree.

In summer, chlorophyll is constantly replaced in the leaves. When it gets cold, the plants stop making chlorophyll and it breaks down into smaller pieces. The trees can reuse the nitrogen that is in the chlorophyll molecule. This is why leaves change colors before they fall off of the tree; the important nutrients that can be reused are taken out of the leaf. The time when leaves start changing color is more dependent on light than on temperature so leaves start changing color at about the same time each year.

When deciduous trees reach this light threshold , carbohydrates are transferred from the leaf to the branch and no new minerals are brought in.

The trees prepare to separate with their leaves. The green color of chlorophyll is so strong that it masks any other pigment. The absence of green in the fall lets the other colors come through. These pigments cause red, pink, or purple colors. Anthocyanins also protect leaves from being eaten or getting sun burned. So the different colors in leaves are caused by changes in the pigments.

When the weather changes, some plants break down all the green pigment. This lets beautiful yellows, oranges, and reds come through in the fall.

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