Leaf Color Changes

1. Q. I know that this has been an unusually hot and dry year but will the weather affect or eliminate what little fall color the local trees do display? My family is from New England and we severely miss fall color of trees.

A. Forget ever having anything close to the fall color of New England in Texas! Trees change colors according to complex chemical formulas. Depending on how much iron, magnesium, phosphorus or sodium is in the tree, and the acidity of the chemicals in the leaves, trees might turn amber, gold, red, orange or just fade from green to brown. Scarlet oaks, red maples and sumacs, for instance, have a slightly acidic sap which causes the leaves to turn bright red. The leaves of some varieties of ash, growing in areas where limestone is present, will turn a regal purplish-blue.

What prompts the change? Although many people believe that a mischievous Jack Frost is responsible for the color change, the weather has nothing to do with it at all. As the days grow shorter and the nights longer, a chemical clock inside the trees starts up, releasing a hormone which restricts the flow of sap to each leaf. As autumn progresses, the sap flow slows and chlorophyll, the chemical that gives the leaves their green color in the spring and summer, disappears. The residual sap becomes more concentrated as it dries, creating the colors of fall.

As the leaves die and fall to earth, the forest begins a winter-long slumber. The leaves, which through the warmer months convert carbon dioxide to oxygen, now take up another task, enriching the soil and providing nutrients for future generations of trees. And by the time this year's leaves fall, next spring's leaves are tightly wrapped in buds ready to unravel in the soft colors of spring.

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