November 23, 2010

One of the joys of the fall season, other than cooler temperatures, is witnessing the change of foliage on the golf course from green to yellow to orange and sometimes to red. Cooler temperatures are often accredited with this beautiful transformation, but another, more significant factor is at work here. The process by which trees shed their leaves is complex, but the reason for this occurrence can basically be attributed to shorter days, or reduced sunlight.
If you remember your high school biology, leaves are green because they contain chlorophyll. Chlorophyll is a green pigment which helps plants carry out photosynthesis. As days become shorter and the amount of available sunlight decreases, trees no longer have the need to produce or keep so much chlorophyll in their leaves. When days get shorter trees use a hormone called ethylene to start withdrawing chlorophyll from their leaves. A second group of pigments, carotenoids, get left behind. Carotenoids are yellow pigments which are present year-round, but are usually hidden by chlorophyll. So, as chlorophyll is taken out of the leaves, they take on the yellowed appearance of carotenoids.
Not all leaves stop at yellow. Some turn orange, or even red. This additional coloring is the result of the presence of yet a third group of pigments called anthocyanins. This set of pigments serves a couple of purposes. First, while the tree is busy removing chlorophyll and other hormones and nutrients from its leaves, it is pretty vulnerable to damage from the sun. Anthocyanins act as a type of sunscreen, allowing the tree to get ready for winter without taking too much damage. Anthocyanins are more often found in trees that prefer colder climates, furthering the belief that they act as protection from the sun. It is also believed that yellow leaves attract aphids, so trees have adapted to prevent this attack by turning their leaves red.
So there you have it! A hormonal response to shorter days gives us one of the most spectacular natural events that occur. Enjoy it while it lasts, miss it while it’s gone, and rest easy knowing we’ll see it again!

This article is contributed by Chris Lare, Assistant Superintendent