As fall winds to a close, I thought it would be appropriate to talk about the wondrous beauty that is on display every year. Many of us look forward to the beauties that autumn brings us each year, but few know why the trees change color every year. This article will explain why the leaves change color, why this is a yearly event, and how the changing colors impact the origins debate.
The beauty of autumn has been celebrated by poets and authors for centuries. However, science took time to catch up to its literary counterparts. Many of us are aware of the process of photosynthesis, which plants use to make their own food. Far fewer know that the cessation of photosynthesis is one of the reasons we see the colors of fall. The process of photosynthesis was unknown until the 1600s and the word itself originated in the late 1800s. Photosynthesis, which will be covered in another article, uses a special pigment called chlorophyll to help convert light into food. Chlorophyll is what gives the leaf its normal green hue. However, as the days shorten and the plants begin to recieve less and less light, the plant begins to prepare to survive the winter. Since they will not be growing during the winter, deciduous plants, such as many common trees, no longer need their leaves to provide nutrients for them. However, the leaves themselves require nutrients to maintain, so they must be removed. Thus the tree begins to form a special seal at the base of the leaf. This seal is called the abscission layer. Made up of cork cells, the abscission layer cuts off the flow of nutrients from the leaf to the plant, but it also cuts off the flow of water from the plant to the leaf. Water is necessary for the leaf to perform photosynthesis. The lack of water causes the leaf to stop producing chlorophyll. As the chlorophyll breaks down, it reveals other pigments not usually seen in the leaf. It is these hidden pigments which give autumn its brilliant, dazzling, artistic pallet.
When chlorophyll is removed, leaves dazzle with brilliant, bright colored displays. These displays are due three different types of pigments. The first is the xanthophylls. Xanthophylls represent the yellow pigment in leaves. The second pigment is the carotenoids. As might be assumed by their name, the carotenoids are responsible for producing the orange pigment in autumn leaves. These first two are present year round. However, the third pigment type, the anthocyanins, only develop after the leaf is cut off from the tree. Anthocyanins form from the sugars trapped in the leaf when the abscission layer cuts it off from the tree. Anthocyanins are responsible for the bright red and purple colors of autumn leaves. When these pigments break down, all that is left are the cell walls, and the tannins, a final pigment type, both of which make the leaf appear a dull, dingy brown.
This yearly artistic display comes about around the same time of year each year. It is so predictable that there are areas that survive based on tourists coming to view the autumnal beauty. There are several reasons why leaves change color around the same time every year. The most obvious one is the change in the length of the days. In the northern hemisphere, towards the end of summer and into autumn, the days begin to shorten, triggering the formation of the abscission layer. However, temperature is also an important part of the process. Shorter days means less energy from the sun reaches the earth, resulting in less heat being retained at night. This causes temperatures to drop. As temperatures drop, chlorophyll breaks down more rapidly. This leads to more beautiful displays, particularly if accompanied by slightly sunnier weather.
We do not tend to think of the autumnal beauty as an origins issue, but it is one, if only in a tangential way. The fact that the dead leaves fall is a designed feature. Were it not for the abscission layer, the tree would have to provide water and nutrients to the leaves throughout the winter, leaving it without the nutrients it would need when the spring growing season started. Further, it is believed that some of the colors, particularly the anthocyanins, are used to ward off insect pests. Such a feature demands a Designer. However, since God made the world for man to enjoy and have dominion over, I believe He made the colors of fall specifically so that man could enjoy them. A feature such as this, which provides both beauty for man to enjoy, and serves a practical function for the tree, points to a God Who made it for those purposes.