Welcome to You Ask Andy

Kelly Saunooke, age 11, of Asheville, N.C., for his question:

HOW DO TREES KNOW WHEN TO SHED THEIR LEAVES?

    Come fall, the lazy woodchuck munches extra food to last him through his long     winter sleep. Flocks of birds fly southward and earthworms burrow down below the     frost. Many small plants shed weatherproof seeds and wither away. Tall trees blush     with candy colors and shed their leafy foliage. Obviously nature is preparing for winter.     But how it all happens is a very complex story our luxurious planet is a seasonal worlds     with warm summers and cooler winters. Summer, of course, is the busy, growing     season, when teeming plants and animals thrive and multiply. Winter is the resting     season, when life slows down.  Spring and fall are between seasons, when plants and     animals prepare themselves for coming changes.  This fabulous story is as old as life     itself, which began billions of years ago.

    Through the endless ages, countless plant and animal species have appeared,     advanced or died out. The survivors were those that adapted and adjusted to the     changing moods and rhythms of the earth. All modern species inherited this wisdom in     biological blueprints from their remote ancestors.

    For example, each species is specially adjusted to the rhythms of day and night.     Bright eyed robins are busy all day and doze when the night prowling owl comes forth     to chase night scurrying mice. Green leaves    make sugar all day and switch to other     duties. after dark.  Each species is adjusted to the day and night rhythm in its own     ecological niche.  So it is with the yearly rhythm of the seasons. In harmony with the     earth's routines, flocks of birds migrate between winter homes and their ancestral     nesting grounds. These planetary adjustments are governed by built in biological     clocks, inherited from successful ancestors.

    In temperate zones, evergreens are shaped to shed the snow and their skinny     needles wear tough, weatherproof coats. Oaks, elms and other deciduous trees have flat,     papery leaves. Frost would turn the sap in their thin walled cells into daggers of ice.     This is why they shed their foliage in the fall and sprout new greenery in the spring.

    The spectacular event occurs on time because it is directed by DNA, the     miraculous biochemical that directs every operation in every living cell. It is the     blueprint that every species inherits from an age old line of successful ancestors.     Among other things, the DNA contains complex biological clocks that adjust all     species.   

     South of the equator, plant life is adjusted to expect midsummer with the     Christmas season. There the deciduous trees have built in instruction to wear their fall       colors at the time when our oaks and elms are sprouting the bursting boughs of May.

 

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