Why Do Leaves Change Color In The Fall?

Nearly everyone who lives in an area of the planet with deciduous trees has taken a walk or a drive to enjoy the colors of autumn. The range of red, orange and yellow that covers the landscape during the fall of the year is a delight to old, young and everyone in between.

But why do the leaves on trees change color in the fall? What makes them go from various shades of green in spring and summer to the wide variety of colors we see before winter comes?

Over the centuries scientists have come to understand a lot about how trees grow and change through the year. One of the key facts they have uncovered is that there is a combination of reasons for the color change we enjoy so much. These are: weather; how long the nights are; and the type of pigment in the leaves.

It may be wise to give a couple of definitions before starting to explain the details of the color change.

Deciduous trees are those that become bare in the winter because the leaves fall off during the autumn season. This is the basis of the common word “fall.” The term can be applied to plants that lose their flower petals and even to animals that shed horns and antlers.

Pigment is the substance that gives living things their color. The process is due to the different levels of absorption of light. In science this might be known as selective color absorption.

Now that we know a little more about trees, color and how the trees lose their leaves we can dig into the reason trees present us with so many beautiful hues in the autumn of the year. The general start of fall’s color change is controlled by the time of year. When the nights grow longer nature takes this as a signal that the season is changing. While temperature and rain have some effect, they can vary considerably. Even the amount of nutrients in the soil and air has some effect, but not as much as the major “night” factor.

Once the nights begin to lengthen the chemical processes in the leaves are slightly different. Trees growing in the spring and summer use a lot of chlorophyll in a process known as photosynthesis. This process makes the sugars that plants use as food, with the help of sunlight. The chlorophyll gives leaves their shades of green.

A substance called carotenoids is also present in plants. This gives some fruits, flowers and vegetables their characteristic orange or yellow color. Another item we should consider is anthocyanins, which provides the purples, deep reds and blues of many fruits.

When nights get longer and the days naturally get shorter, production of chlorophyll slows down considerably. As the chlorophyll becomes less dominant and eventually disappears the carotenoids and anthocyanins are revealed. Depending on the amount of each in various species, colors vary from dark red and orange to yellow and gold.