Why do leaves change colors?

For Southern Utah University students, autumn can mean several things: football games, the return to campus, cooler temperatures and that feeling that winter is slowly but surely on its way. Arguably, most students are especially excited for the colors of fall. The red, orange, yellow and brown leaves are a sight to behold as you walk around Cedar City. As you wander, you may stop to wonder why leaves even do change colors; luckily, the U.S. Forest Service explains this phenomenon. 

This question has been on the lips of scientists all over the world, and progress is being made to fully understand this process. The biggest factors include leaf pigments, the length of night and weather. While elements like food supply and rainfall also contribute to this change, the most important part is the shorter period of daylight that occurs in winter.

Unfortunately, leaves do not have a great way of adapting to rapidly changing conditions. As the days grow shorter, they have less time to gather sunlight, and biochemical processes begin to take place that change their colors and create the breathtaking sceneries of autumn.

It’s important to note that leaves change color and fall at different times depending on the climate of the area they are in. For instance, fall colors will hit Cedar City faster than they will in St. George due to the more mountainous location and its higher elevation level. 

Three types of pigments play a role in what color the leaves become: carotenoids, anthocyanin and chlorophyll. Chlorophyll helps leaves photosynthesize, which creates their familiar green hues. Carotenoids are responsible for the yellow, orange and brown colors, while anthocyanin appears as red. As the seasons change, chlorophyll stops being able to grow, revealing the other two pigments before the leaves eventually fall.  

Every kind of tree exhibits this process differently. For example, oak trees tend to take the longest to change, often doing so after other trees have already lost their color.

Some trees have adapted to their environment in a way that lets them keep their greenery throughout the winter. Oftentimes, these broad-leaf or evergreen trees are found in mountainous areas where overnight temperatures, even in the heat of summer, can be chilly.

Fall makes for a spectacular show of colors that students can enjoy around SUU until the season ends, all thanks to the complicated process leaves undergo. On a walk around campus, a deeper look at autumn can be enjoyed before the multicolored leaves are replaced with snow. 


Author: Keller Sherman
Photos courtesy of SUU
Editor: Lily Brunson