Why do leaves change colors in the fall? We certainly appreciate that they do, but the reasoning behind it may be mystifying to most. Perhaps that’s what makes it magical. Or perhaps, learning why and how it happens may be the most magical part of it all.
Throughout the spring and summer, leaves are full of chlorophyll – the substance responsible for converting sunlight into energy in the form of glucose. This process is a little thing called photosynthesis. (Sound familiar?) Chlorophyll is also what makes leaves look green.
During the long, sunshine-filled days of summer, trees are getting happy and fat, converting sunshine into glucose, storing it and growing. Basically, it’s like Thanksgiving Day all summer long for trees. But, all good things must come to an end. As summer winds down and days begin to get shorter and colder, photosynthesis also winds down.
When the trees begin to shut down in response to shortening days, chlorophyll is no longer needed. As chlorophyll breaks down and disappears, so does the green color that’s associated with it. This process leaves other things behind – things that were in the leaf all along, but were not visible because of the vivid green of the chlorophyll.
For maple trees, glucose gets trapped in the leaves and are converted to antioxidants (similar to those found in purple grapes, red apples and some flowers), turning them a bright, head-turning red or orange color. But not all trees are as fortunate as maples. Live oaks, for example, trap waste products inside the leaves, turning them a dull brown.
But why do they shed leaves at all? Most plants need some way of replenishing leaves that have been damaged by insects, storms or diseases. Deciduous trees deal with that by dropping leaves in the fall and re-leafing in the spring. The needles on evergreens are generally a little more resistant to damage which enables them to hold onto them for a longer period of time (2-year old needles are shed each fall; needles produced that growing season are retained).
So, enjoy the show this fall and remember the amazing, behind-the-curtains work that was required to pull it off.