The Science Behind Leaf Color In The Fall . . .

Many deciduous trees and shrubs provide spectacular color in the fall once they begin to go dormant for the winter. Fall coloring is caused by the pigment remaining in the leaf once photosynthesis slows down and the green chlorophyll is depleted. This color can be intensified by periods of sunny, warm days and crisp, cool nights. Fall color is somewhat unpredictable, but always a delight.

Once summer ends, the days get shorter, due to the changes in the angle of the sun....   

 

Here is a brief description of the science behind Fall Color:

Plants take water from the ground through their roots. They absorb carbon dioxide from the air. Plants use sunlight to turn water and carbon dioxide into oxygen and glucose.

Glucose is usable food for the plant’s growth.

Plants turn water and carbon dioxide into oxygen and sugar.  This is called photosynthesis ("putting together with light").

Chlorophyll is a chemical that gives plants their green color and helps make photosynthesis possible. 

The month of October is often one of the driest months of the year.  This also ques the plants into realizing  that they need to go dormant.

This lack of light and water cuts off photosynthesis, allowing the trees to rest, and live off the food they had stored during the summer. 

As the chlorophyll disappears from the leaves, the emergence of yellow and orange colors begin to show up. Small amounts of these colors have been in the leaves since the previous spring, but have been hidden by the abundance of green.

The bright reds and purples we see in leaves are made mostly in the fall.

In some trees, like maples, glucose is trapped in the leaves after photosynthesis stops. Sunlight and the cool nights of autumn cause the leaves to convert the glucose into a red color.

 The brown color of trees, like some oaks, is made from wastes products left in the leaves.

"Evergreens" are another science marvel.  They keep most of their leaves, or needles, during the winter and continue to photosynthesize, if provided enough water. Their growth is slowed down due to colder temperatures. Their special leaves, or needles, are resistant to cold and moisture loss. Evergreens may continue to photosynthesize during the winter as long as they get enough water, but the reactions occur more slowly with cooler temperatures.