Last weekend at a Saturday morning football game, my Grandson asked me why leaves change color? I think I get asked this question every fall.
So, why do autumn leaves change their color?
It all starts with photosynthesis. Leaves typically produce their vivid hues of green from
spring through summer into early fall through the constant creation of Chlorophyll. As we all
learned in grade school science, Chlorophyll is the key component in a plant’s ability to turn
sunlight into glucose, which in turn feeds the trees. In Spring and Summer, millions of these Chlorophyll cells saturate the leaves, ultimately making them appear green to the eye. Without the presence of Chlorophyll in the leaf, the bright golds, reds, yellows, and browns would be the natural colors seen year-round.
Chlorophyll isn’t the only thing involved in leaves changing color, however. Present in other leaves and trees are the compounds known as Carotenoids and Anthocyanins. As the Fall days begin to get shorter and shorter, the production of Chlorophyll slows to a halt, eventually giving way to the ‘true’ color of the leaf.
Flavonols are always present in leaves and give them the yellow color when chlorophyll production slows down in the fall. Beta-carotene is the most common carotenoid present in most leaves. It absorbs blue and green light, and reflects yellow and red light from the sun and gives leaves their orange hue when chlorophyll production drops. In the fall anthocyanin production increases. This compound protects the leaf through the fall and gives leaves their red color.
So, why do leaves fall?
Perennials, which includes trees, must protect themselves in order to get through the harsh, freezing temperatures of winter. If trees did not shed their leaves, their soft vegetation would certainly freeze during winter time, damaging and, no doubt, killing the tree.
In order to cope with the grueling winter temperatures, trees slowly close off the veins that carry water and nutrients to and from the leaves with a layer of new cells that form at the base of the leaf stem, protecting the limbs and body of the tree. Once the process of new cell creation is complete, water and nutrients no longer flow to and from the leaf. The leaf will die and weaken at the stem, eventually falling to the ground.
What happens to the leaves?
Mother Nature is fantastic at recycling. Whether through the water cycle, or the slow process of decomposing plants and trees back in to soil, the Earth wastes very little. When leaves fall to the ground, they begin to break down and eventually create a rich humus on the forest floor that absorbs dew and rainfall. This nutrient-rich ‘sponge’ acts as a continual source of nutrients and water for trees and plants, helping to promote life and plant health in the next spring season.
It is not difficult to conclude that while the falling of the leaves protects the trees through winter, it’s likely that trees would not survive as well without the rich layer of dead leaves through the warm spring and summer months. In this way, trees’ natural cycle provides health and sustainability for itself year after year.
Conservation Corner is a weekly article produced by the Forest County Land & Water Conservation Department. For more information contact Steve Kircher, County Conservationist-Land Information/GIS Director at 715-478-1387 or by e-mail at .