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Why Do Leaves Change Color?

Posted on Sep 9, 2014

Have you ever wondered why the lush green summer colors of the local trees and shrubs change as autumn approaches? Well, as the length of daylight shortens and the intensity of sunlight lessens, chlorophyll production slows down and eventually stops within the leaves. As the chlorophyll gets broken down and disappears, the carotenoids and anthocyanins (other chemicals that exists in the leaves) become unmasked as the green color fades, revealing brilliant shades of oranges, reds and yellows. While this process is occurring, another is at work. The veins that carry fluids and nutrients in and out of the leaves slowly begin to close off as a layer of cells build up at the base of the leaves. Once the vein is completely sealed off, the leaf will subsequently fall and leave nothing but a small leaf scar on the branch from which it fell.

In just a few weeks these trails in Long Point will be lined with bright oranges and reds as the leaves begin to change.

In just a few weeks these trails in Long Point State Park will be littered with brightly colored leaves.

Now, how is this process good for the tree or shrub? Couldn’t the leaves still produce nutrients through photosynthesis on those bright, sunny winter days? Broad-leaf trees, like our maples, oaks, and aspens for example, have very thin and wide leaves. The leaves cannot withstand their cells freezing and therefore can be easily damaged by ice crystal formation, which could render them unable to produce nutrients for the tree itself. If the leaves are shed before freezing temperatures arrive and the tissues are sealed off from which they were once connected, it can protect the tender twigs and enable them to produce new leaves the following growing season. Likewise, shrubs do this for the same reason, as most shrub leaves aren’t hardy enough to withstand the region’s cold temperatures either. Most coniferous trees on the other hand, such as pines, spruces and hemlock, can retain their leaves, or needles, as they have a thick, waxy coating that provides protection to the sensitive cells within them.

Soon the deciduous trees in the region will be displaying bright oranges, reds and yellows.

Soon the deciduous trees in the region will look a lot like this!

Lastly, how does weather influence the leaves? Although day length typically determines when the leaves begin to change color and fall, the weather conditions can cause some delays in how soon they change. In years of late springs or long droughts, the color change could be delayed by weeks depending on the severity of the conditions. Furthermore, weather can influence the intensity of the colors as well. For example, warm and wet conditions throughout the spring and summer along with warm fall days and cool nights can produce the most brilliant colors. Early frosts or warm nights in the fall can cause colors to be more dull in contrast. Although we still have a while before the leaves really start to change, my hope is this past spring and summer’s wetness and (mostly) warm temperatures will help produce a vibrant autumn display here in Western NY.

So with all of that said, take a peek outside or check a foliage map and get out this fall to enjoy the region’s beautiful colors and creatures that will be around, I know we will!


Elyse Henshaw
Conservation Technician