Why Do the Leaves Change Color?

For most, the months between September and December are characterized by colder weather and the changing colors of the leaves before they reach the ground. The combinations of green fading to a myriad of colors like red, orange, yellow and sometimes even purple draws many people out of their homes and to the trails. However, do you know why the leaves change color each year? The process is a lot more chemical than you’d think. 

Green leaves during the spring and summer function as the producers, almost like an energy factory, for the overall plant. Doing the hard work of converting sunlight into plant energy happens all within the leaf’s many microscopic cells. These cells contain the pigment chlorophyll, which is essential for the process of photosynthesis to take place. Through the input of light and chlorophyll alone is how a plant is able to convert carbon dioxide and water to feed itself and grow. However, there are other pigments that are present in most plants which range from yellow to orange, such as carotene and xanthophyll, which for example make carrots orange. These colors are often not seen, however, because the overwhelming presence of chlorophyll and the color green drown out these other chemical pigments. 

 As the seasons begin their change, it coincides with a smaller amount of overall daylight length and colder temperatures. All of this functions as a signal to the leaves to stop the process of converting sunlight into plant food and to prepare for the dormancy of winter months. As chlorophyll breaks down, the green color of the leaf also breaks down, allowing the yellow and orange colors of other chemical pigments to become visible. Other colors also become visible through new chemical reactions which occur as chlorophyll breaks down, such as the creation of red anthocyanin. 

Many trees have different colors throughout the many chemical processes. Dogwoods and sumacs tend to have deeper hues of red and purple where many oak trees display browns. Some, like the sugar maple, have vibrant colors of orange. 

It is also important to note that there are many other different factors which influence color, specifically the saturation of the color. The specific light levels, the precipitation and specific water amount the plant receives, as well as the overall temperature also influence both the intensity of color as well as how long the leaf continues to hold that color. 

In regards to some of the trees that consistently produce amazing leaf color, the Arbor Day Foundation has compiled a list of its top 8 trees which produce amazing color.

1. Black Tupelo
   
2. Ginkgo
   
3. Shumard Oak
   
4. Red Rocket Crapemyrtle 
   
5. Kentucky Coffeetree
   
6. Sugar Maple
   
7. Red Maple
   
8. Sourwood
   

Interestingly enough, all of these trees, with the exception of Red Rocket Crapemyrtle and Sourwood, can survive through Indiana winters and may even be in your backyard. Monroe County, and most of southern Indiana, fall squarely within zone 6 of plant hardiness. However, Red Rocket Crapemyrtle and Sourwood may still be found throughout much of the Midwest. 

Whether we are driving home from work or we are seasoned field guides, it is impossible to miss these incredible demonstrations of color from the natural world. There are a number of trailheads throughout Monroe County ranging all skill levels. Send your best photographs of the trees and their changing leaves to monroecsoil@gmail.com for a chance to be featured!