Why Leaves Change Color, as Fall is Finally Here

Fall Fiesta Sugar Maple (Acer saccharum 'BAILsta')

Fall Fiesta Sugar Maple (Acer saccharum ‘BAILsta’)

Fall is officially here, proven true by the yellowed Honey Locust leaves raining down outside my office window. This weekend provides a perfect opportunity to explore the changing colors across the state, with gorgeous weather and many opportunities nearby. As you’re enjoying the beautiful scenery, you may be wondering – why do leaves change color?

The change in leaf color indicates a physiological shift within woody plants as they close down for the winter. This change is spurred by cooler night temperatures and a shorter day length. Since sensitive leaf tissues would not survive the cold weather ahead, woody plants shed the leaves before the winter comes.

Losing all those leaves may seem like a waste of resources for the tree, especially since the leaves are often blown away before they break down to return nutrients to the soil. To reduce the amount of nutrients lost, unnecessary cellular structures are broken down within the leaves. The nutrients recovered from these cellular structures are then re-located into the vascular tissues, which are protected by the bark of the woody plant for the winter. These resources are saved for creating new leaves the following spring.

Chlorophyll, responsible for plant photosynthesis, are one of the primary cellular structures that are broken down in fall. As these structures are removed, so is the green color synonymous with photosynthesis. In the absence of green chlorophyll, the many other pigments within tree leaves are allowed to shine, giving way to colorful leaves of yellow, orange, red, and purple.

Who knew recycling could be so pretty?