October 7, 2012

How and why leaves change color


Some say the bear was met by spirit hunters who continue to hunt him to this day, and the bear can still be seen in the night sky as the constellation Ursa Major. As the Great Bear constellation rises above the horizon in the fall, his blood drips down onto the trees below, turning the leaves scarlet red.

Others say the bear was killed by the spirit hunters and that, as the Great Bear died, its blood fell upon the trees, turning the leaves red. As the spirit hunters cooked the meat, fat dripping from the fire fell upon other trees, turning their leaves orange and gold. Mother Earth, in honoring and remembering the great bear, turns the leaves those same colors to this day.

In European folklore, children were told of an elf named Jack Frost who freezes the ground with his chilly feet, paints lacy white pictures on the winter window panes and turns the leaves colors with the icy touch of his fingers.

The real answer lies in first understanding how trees manufacture food by photosynthesis, which means putting together with light. In spring and summer, essential nutrients and water travel from the trees’ roots to their leaves. At the same time, carbon dioxide is taken from the air.

Chlorophyll, a pigment found in green plants, absorbs energy from the sun and uses it to transform carbon dioxide and water into sugars, which the tree either uses immediately or stores as carbohydrates until it is needed. Oxygen is released into the atmosphere as a byproduct. So, I guess you could say chlorophyll is the source of life. It also gives the leaves their green color.

With the coming of fall and shorter, cooler days, the trees must ready themselves for winter, when they will not have enough light or water for photosynthesis to occur. Subtle chemical changes take place. Water flows out of the leaves into the roots, where the nutrients can be stored. As the leaves stop producing food, the chlorophyll breaks down and the green pigment in the leaves slowly disappears.

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Peter Black: Canadian Dispatch
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