How do Leaves Change Colors in the Fall?

Several factors contribute to fall color, but the main agent is light, or actually the lack of it. As the autumn days grow shorter, the reduced light triggers chemical changes in deciduous leaves causing a corky wall to Fall colors - redform between the twig and the leaf stalk. As the corky cells multiply, they seal off the vessels that supply the leaf with nutrients and water, and also block the exit vessels, trapping simple sugars in the leaves. The combination of reduced light, lack of nutrients and no water, add up to the demise of the pigment chlorophyll, the “green” in leaves.

Once the green is gone, two other pigments show their bright faces. These pigments, carotene (yellow) and anthocyanin (red) exist in the leaf all summer but are masked by the chlorophyll. The browns in autumn leaves are the result of tannin, a chemical that exists in many leaves, especially oaks.

Sugar trapped in autumn leaves by the corky cells also known as the abscission layer is largely responsible for the vivid color. Some additional Fall colors - yellowanthocyanins are also manufactured by sunlight acting on the trapped sugar. This is why the foliage is so sparkling after several bright fall days and more pastel during rainy spells. In general, a dry fall produces the most vibrant color.

Weather conditions in summer and early September, largely determine how brilliant each season’s colors will be.  According to David Beachler, meteorologist at the National Weather Service in Grand Rapids, a hot, dry summer inflicts stress on the trees; therefore, when it cools, the chlorophyll that breaks down in the leaves can produce a quick colorFall colors - orange change. Autumn rain is desirable, but continuous cloudy weather is not, since that would stop the production that creates the brilliant reds and golds found in oaks and maples, Michigan’s most prevalent tree species.

There are nearly 150 different species of trees in Michigan’s 18.6 million acres of forest.  Our state boasts a colorful mix of yellows, reds, golds and oranges. Some of the most beautiful colors are displayed by such hardwoods as aspen, maple, birch, sumac and oak.  When combined with a background of evergreen forest, the result is one of the best shows in the nation.

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