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Why Do Trees Need Sunlight?

By Lesley Barker

Without trees, the world would be a lot less beautiful. Lots of animals would lose their habitats. Many nuts and fruits would not be available, and what would we do without wood, rubber or paper? Perhaps the most important role of trees, though, is how they use sunlight.


Some trees are evergreens and do not shed their leaves every year. Others are deciduous and lose their leaves each autumn. New leaves grow in the spring. Whether or not the leaves have an annual cycle, it is inside the leaves where trees process sunlight.


The only parts of a tree that are green are the leaves. The green areas of plants contain chlorophyll, the green pigment that is responsible for absorbing sunlight. There the light energy combines with carbon dioxide in a process called photosynthesis. The result is sugar to feed the plant and oxygen, which is released into the air.


In addition to providing nourishment for the trees themselves, the process of photosynthesis uses up the carbon dioxide from the air. People exhale carbon dioxide. When we burn fossil fuels, carbon dioxide is released. This contributes to the problem of global warming, which threatens to hurt our climate and the earth. One of the most valuable things that we can do to prevent global warming is to plant more trees.


Trees block half of the sun from the rest of the plants in a forest area. This is one reason that the tallest trees in the forest tend to be the species that get their spring leaves later than the other plants. When a really tall tree dies, the saplings that have been growing in its shade spring up. There may be several saplings near a mature tree that stay fairly short until the dead tree exposes them to the light. Then the sapling that grows the fastest will dominate the forest canopy, and the other smaller trees may die.

Time Frame

Only a few species of trees can tolerate less than half a day of sunlight. These tend to be the shorter trees in the forest. They include birch, dogwood, magnolia and redbud trees.


About the Author


Lesley Barker, director of the Bolduc House Museum, authored the books "St. Louis Gateway Rail—The 1970s," published by Arcadia, and the "Eye Can Too! Read" series of vision-related e-books. Her articles have appeared in print and online since the 1980s. Barker holds a Bachelor of Arts in sociology from Washington University and a Master of Arts in Teaching from Webster University.