Like clockwork, every fall leaves begin to change from their bright greens to several vibrant colors.
For many this usually occurs during the months of September and October, with leaves gradually beginning to fall off during the peak of the fall season. However, this year a wrench has been thrown into the leaf-peeping season, as the drought that gripped a large portion of Mid-Missouri is delaying the change in colors.
Several factors influence the arrival of fall colors, which according to the United States National Arboretum include a wet growing season followed by a dry autumn and plenty of sunny days with cool, frost-free nights. A combination of these factors results in the brightest display of fall colors, which parts of the upper Midwest are beginning to see. However, changes in weather can significantly affect when fall’s foliage arrive.
A significant factor in the delay is drought conditions during the summer months, which is what Mid-Missouri saw all summer long. Droughts cause trees to shut down early to prepare for the winter season. This essentially causes trees to shed their leaves before they reach their vibrant colors of fall.
The early shutdown causes leaves to brown and fall more quickly than they normally would and in some cases can delay the onset of fall colors. Freezing temperatures, which parts of Mid-Missouri have already experienced, can actually lead to poor fall color as it kills the chemical process happening inside a changing leaf. It’s the perfect recipe for Mid-Missouri to not experience a dazzling array of fall colors.
While Mid-Missouri is beginning to see some patchy fall colors develop, it’s likely the freeze that we just saw will bring an end to the fall foliage. However, any trees with leaves that survived the recent rains that alleviated the drought conditions and light winds that followed could yield a nice peek of fall colors as we head into late October.
What causes these leaves to change? It has a lot to do with the annual cycle of a tree.
During ideal conditions in the spring and summer, the leaves (the workhorse of the tree) make the food necessary for the trees to grow. This process takes place inside the plant’s cells that contain chlorophyll, which is best known for giving trees their bright green colors. In high school biology, many learned that this chemical takes in energy from sunlight that is used to turn carbon dioxide and water into carbohydrates. There are other pigments within a leaf, but because of the hard work of chlorophyll during the growing season, those colors are dull compared to the bright green.
As summer comes to an end and the daylight begins to shorten, trees receive a signal to stop making the food they need and gradually begin to shut down. This causes the chlorophyll to break down, eliminating the green color and allowing the other pigments (yellows, orange and red) to break through and shine, which is actually the leaf’s true color.
This gradually leads to the leaves falling off through a process in which the leaf tissue is cut off from the tree, allowing the leaves to fall or blow off in strong winds.
Not all trees shed their leaves, but a large portion of trees in Mid-Missouri go through the process. Those that don’t shed their leaves are known as evergreens, which keep their green leaves through the winter.
Current weather conditions support changes in leaves here in Mid-Missouri, but it’s likely the summer drought will play a big role in keeping many colors dull. Some tress might show no fall color at all. Current estimates show that peak colors for Mid-Missouri will likely exist as we close out October and welcome in November.
Stay with ABC 17 Stormtrack Weather as we continue to monitor the changing weather patterns and the cooler weather that will follow.