Have you ever looked at trees, really looked at them? If you have, then you know how very different trees are from one another. The tallest trees reach 110 meters up into the sky and some trees are only 4.5 meters tall. Some trees are broad and some are narrow. Some lose their leaves in the winter and some don't. In autumn many trees can have green leaves, while others have leaves that burst with color. As you can see, trees are amazingly diverse!

Trees that have leaves that change color in the fall and drop to the ground are called deciduous trees. Many people think deciduous trees lose their leaves because of cold weather and frost, a common misconception, but actually the length of the day determines when trees begin the process of dropping their leaves. If you live in a climate where it is warm for most of the year, you know that deciduous trees keep to a schedule, and each fall they change colors and lose their leaves just like their counterparts in colder climates. Trees are able to "rest" during the winter when they do not have leaves. This actually lets trees conserve energy.

No matter where you live, as the seasons change from summer, to fall, to winter, the days shorten, bringing less of the sunlight necessary for the trees to produce chlorophyll. Chlorophyll gives leaves their basic green color and has the unique capability to capture sunlight for photosynthesis. Photosynthesis is a chemical reaction that enables plants to use sunlight, water, and carbon dioxide to produce food for the tree in the form of sugar. In winter, there is not adequate sunlight for the tree to produce enough sugar to keep it healthy and growing; therefore, the process of photosynthesis in deciduous trees stops, the trees becomes dormant and wait for spring to return.

As a tree begins to prepare for winter, chlorophyll is no longer produced and starts to break down. As the chlorophyll begins to fade away, the other colors in the leaf can finally show their true intensity. The fall colors were always there; they were just hidden by the abundant amount of green color produced by the chlorophyll. Two pigments called carotene and anthocyanins create the other colors in the leaves. Carotene will persist in leaves even when chlorophyll has disappeared, causing the leaves to change from green to a yellow, orange, or brown color. In some trees, when sugars produced by the leaves can no longer flow from the leaf to the tree, anthocyanins form in the leaf. This reaction causes the yellowing leaves to turn red, blue, and purple.

Pigmentation in the leaves and the length of the days are just two factors that affect the color of leaves in the autumn. A third factor is weather. Weather conditions that occur before and during the time the chlorophyll is fading from the leaf can cause the fall foliage to vary from spectacular to drab. Temperature and the amount of water in the soil are the main influences on the richness of color. A lot of sunny, warm days, with cool but not freezing nights, seem to produce the best colors in the fall. However, a really warm period in the fall will keep the leaves from being brilliantly colored, and if the soil does not have enough moisture due to a summer drought, leaves may not change colors for as long as a few weeks.

One interesting idea for this color change is that leaves change color as a signal to insects that could damge them. The brighter color can tell insects they have changed the amount of food they can offer to insects.

You can see the colors of autumn in parks and forests, in the city, and in the countryside. The next time you feel a bit of a chill in the air, you will know that autumn is on its way and that it is time to watch for the beautiful explosion of color. Look carefully at the different trees, really look at them and see how many different shades of yellow, orange, red, purple, and brown there are. Look closely, even more colors might be hidden, waiting to burst forth.