Monday, November 14, 2011

Why Foliage Turns in Autumn

With the overnight freeze several weeks ago it seemed destiny had planned to deny us the annual foliage show this year. After the horrid summer, we truly needed something that returns each year without fail and as though through a collective wish our native trees began their color change. As the clocks were turned back suddenly shades of gold were seen shimmering in the breezes... the native hardwoods, who are naturalized and hardy, have not disappointed us. Trees lose their leaves to give additional sunlight for warmth during the cold winter months and Nature has provided us with a stunning visual as a parting gift.

Although the following explanation will be a vast over simplification, it may provide insight into the foliage change. During the spring and summer the trees use their leaves to collect air and water utilizing a process called photosynthesis to turn it into food. Photosynthesis means ‘putting together with light’ so as the days shorten and daylight diminishes, the gathering process ends. The leaf is no longer necessary to the tree and begins its fall transformation. Suddenly the hillsides become a dramatic autumn palette that provides breathtaking color for a brief moment in time.

The chemicals chlorophyll and carotenoids are present in the leaf cells throughout the growing season with chlorophyll making leaves the bright green color associated with the photosynthesis process. As darkness increases in the autumn, chlorophyll production eventually stops and inevitably all the chlorophyll disappears. With the loss of chlorophyll, the carotids become visible and provide the leaves with lovely yellow colors. Lastly the anthocyanins may arrive and take center stage, ushering in the vibrant reds we associate with Autumn.

Because carotenoids are always present in leaves the amber, yellow and gold colors remain fairly constant from year to year, even during drought. However conditions must be ideal for the fickle anthocyanins who are glucose (sugar) and singularly responsible for the brilliant hues of purple, crimson, and scarlet. To be spectacular the tree requires warm sunny days and cool crisp evenings to slow the closing of the leaf veins and trap an excess of sugar produced at this time. Due to our erratic weather of late, the reds this year will probably be lackluster at best.

However the shade and foliage show are not all the leaves have to offer… their parting gift is perhaps the most important. The leaves drift from the trees and collect below to continue their work by slowly decomposing. Over time they add nutrients to create a dark rich soil which nourishes fledgling saplings as they grow to become forest giants like their parents. It is indeed a miraculous cycle of life!

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