What happens to a tree's leaves each fall?
Have you ever wondered why the leaves of the Arboretum’s trees change into a dazzling array of red, orange, yellow, and purple each fall? If you have walked around the Arboretum recently, there is no doubt that you have seen this impressive display. Read on to learn how trees achieve this mesmerizing feat.
Have you ever wondered why the leaves of the Arboretum’s trees change into a dazzling array of red, orange, yellow, and purple each fall? If you have walked around the Arboretum recently, there is no doubt that you have seen this impressive display. As deciduous trees prepare for the harsh winter ahead, they lose their leaves to conserve resources and resist being blown over during the windier winter months. Chemical changes inside the tree and its leaves control this process. The fall colors we see are a beautiful result of this leaf degradation process.
The reason we see different colors in leaves is due to chemicals called pigments. Four main types of pigments make up leaves: chlorophyll (greens), xanthophylls (yellows), carotenoids (oranges), and anthocyanins (reds). Chlorophyll is a light-capturing compound that is important in photosynthesis, which is the process by which plants harness energy from the sun and produce their own food. Throughout the sunny spring and summer, photosynthesis is in high gear, and tree leaves appear bright green due to their high content of chlorophyll, which is hard at work capturing energy from the sun.
As the days get shorter, colder, and darker, leaves get the message that it is almost time for winter. Animals are not the only ones to use hormones as chemical signals—plants also rely on hormones to relay messages throughout the plant. Before the leaves fall and dance to the ground, the trees reabsorb valuable nutrients from the leaves and store them in their roots. The leaves stop their food-making process and stop creating chlorophyll. Chlorophyll is one of the first molecules to be broken down for its nutrients. As chlorophyll breaks down, the green color of the leaves begins to fade, and the red, orange, and yellow pigments in the leaves become visible. Eventually, the trees drop these brightly-colored leaves to the ground in a process known as abscission, which occurs when hormones signal specialized cells to actively cut off the leaves. Hormones in the tree control both the color changes and the dropping of the leaves.
Now, the next time you walk around the Arboretum, you can have a greater appreciation for all of the chemical changes that occur to create the kaleidoscope of colors that tower above your head and lie below your feet. If you haven’t had a chance to visit the Arboretum, now is the time to observe peak fall foliage and witness the amazing abilities of our artist known as Nature.