Friday, November 7, 2008

A play of color

by Carrie Karl, WREN Environmental Education Assistant

The change of seasons is upon us, fall is in full swing and this year it brings a myriad of color. Our palette of vibrant summer greens has given way to brilliant oranges, yellows and reds. The three pigments that are the main characters in our fall play are chlorophyll, the greens, carotenoids, the yellows and oranges and anthocyanins, the reds and purples. Chlorophyll and carotenoids are always present in the leaf of the tree. Anthocyanins are produced during the fall.

As fall begins in the West Eugene Wetlands temperatures decrease and nights grow longer signaling to plants the approach of winter. Plants reflect this change in season by beginning to seal off their leaves via swelling of a special layer of cells at the base of the leaf called the abscission layer. As this layer swellschlorophyll and carotenoids, are trapped. The ensnared chlorophyll continues the process of photosynthesis producing a build up of sugar in the leaf. Sugars combined with bright light produce the anthocyanins. As the chlorophyll is exhausted the carotenoids and anthocyanins are exposed painting the landscape with bold strokes of color.

Many factors influence the brilliance of fall color. However, the best color occurs after a period of dry, warm sunny days with cool crisp nights. The nights must remain above freezing to allow for a slow swelling of the abscission layer which prevents the sugars from moving out of the leaf. The more sugar in the leaf, the more brilliant the anthocyanins. Carotenoids, however, are always present in the leaf and as a result are usually the same from year to year.

The beauty of the fall colors persist beyond the tree. When the nights cool enough to allow for the abscission layer to swell completely, the leaf is then forced off the tree. The tender leaf tissues would not survive the winter so the tree must shed them. These cast offs will decompose providing nutrients to the soil or food for organisms. The color will eventually fade exposing the tannin, browns, that lie beneath.

The drama of the fall play lies in the passing splendor of the colors, and yet, the real story is the leaf. It sustains the tree while it graces its branches during the summer producing food for survival. As fall begins the leaf radiates its inner brilliance and with the start of winter it falls to the base of the tree replenishing the forest floor and the place, the tree calls home.

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