If you were out and about the 705 during the Labour Day weekend, you may have noticed that some trees are already starting to show off their fall colours. For most of us, the sight of the leaves changing colour is a signal that fall is officially here. Indian legend has it that celestial hunters slew the Great Bear Autumn and the spilled blood turned the leaves red. The yellow of fall came from the fat splattering out of the kettle as the hunters cooked their prize. We know today that the changes are the result of chemical processes taking place in the tree as the growing season ends.
Trees that have leaves that change color in fall are deciduous. Evergreen trees with needles, which stay green to continue the photosynthesis process through the winter, are coniferous. Deciduous trees usually have large, broad leaves. Some of the most common in our neck of the woods include birch, beech, ash, poplar, elm, oak, tamarack and, of course, maple.
Leaves contain disk-like structures within cells called ‘chloroplasts’ that produce food for the tree. This process is called photosynthesis, where light energy is converted into chemical energy. Light is captured and used to transform carbon dioxide and water into oxygen and sugars. Chemical energy gets stored in sugars and is converted into food.
Chloroplasts contain chlorophyll, a pigment which gives leaves their green colour. During spring and summer, the ample daylight gives plants plenty of time in the sun, and they produce chlorophyll regularly. However, as fall begins, sunlight hours shrink, and the temperatures cool down. Since the leaves are no longer able to produce food for the tree, they break down chlorophyll, and orange and yellow pigments, called carotene and xanthophylls, surface. Carotenoids are also found in bananas and carrots.
The vivid reds come from pigments called anthocyanins which are manufactured from sugars in the leaf. Anthocyanins are also found in cherries and cranberries. Some trees, like oaks and dogwoods, are likely to produce red leaves. The sugars are stored in the twigs for next spring when leaves emerge again.
This cyclic pattern repeats itself every September in countries that experience seasonal weather. The quantity and quality of the colour vary depending on weather, sunlight and soil moisture. Then, of course, the leaves fall. Trees start building a protective seal between leaves and their branches as the weather turns. They take in as many nutrients as possible from the leaves, but leaves wouldn’t survive the winter and would make trees vulnerable to damage if they remained. When the leaves are cut off from the fluid in the branches, they separate and drop to the ground.
The Ontario Fall Colour Report is already tracking this year’s autumn leaves. You can check it out on the Discover Muskoka website. The website is also packed with info about where you can find the best spots to view the fall colours, and a list of the great autumn events across the region. We highly recommend checking it out!
