Why Leaves Change Color
Every year in temperate countries and on rare occasions in tropical countries that have wintering trees, we see leaves change color and fall to the ground, carpeting the earth. The change in color can be really beautiful. Leaves usually go from green to brown, red, yellows, blues, or varying hues of orange. This color change marks the beginning of autumn.
So what is happening to the leaves? We know that leaves are the centers of photosynthesis and they provide food for much of the plant or tree. If the leaves fall off, won't the plants die? To understand how leaves can change color, we first have to understand what is inside the leaf. Apart from chlorophyll, which turns the leaves green during spring and summer, leaves also have carotenoids (found in the plastids) and anthocyanins (found in the sap of the cells.) These are pigments that leaves contain other than the green pigment. However, because leaves need the chlorophyll to make food, chlorophyll usually works overtime during the spring and summer and in effect masks the other pigments found within the leaves.
As winter approaches, factors within and outside of the leaf begin slowing the production of chlorophyll. Namely, the veins that carry water onto leaves slowly close off by adding a cork layer at the base of each leaf. This slowed production allows the other pigments to show and that is why the leaves appear to change color. Eventually the leaves will fall off either from the wind or from its own weight. Once the tree's leaves have completely changed color and begin falling off, food production stops. Throughout the winter, the plants will use the food that they have been storing during the spring and summer, usually this is stored in the roots of the plants, but other plants have different places of storage as well.
There are several reasons why leaves change color. The first reason has to do with animal and plant interdependency. The changing colors signal animals that the winter is coming. This is especially true for certain insects. When leaves change color, the insect is no longer attracted to the leaf. With fewer leaves to eat, the insect is forced to toughen up for the winter.
Next, the leaves of plants change color in order to protect the plant from light at low temperatures, something that can be harmful towards plants and trees. If the plant's leaves are of a different color and the leaves are not focused on producing food, the plant's energy can focus on reabsorbing nutrients needed for the winter.
Finally, the falling of the leaves creates a natural blanket of dead matter on the forest or wood floor. This dead matter can decay during the winter, creating good fertilizer that the trees and plants can use and need during the spring when they begin growing their leaves. This carpeting is a natural form of fertilizer that nature does all on its own. It also keeps the ground warm by shielding it from the snow, which helps the plant's roots from becoming too cold and dying during the winter.
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