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Falling Leaves

Fall 2003 Newsletter

Autumn is a colorful time in Northwest Illinois. The leaves slowly change color, green giving way to yellow, orange, scarlet, deep red, and shades of brown and tan. More than any other feature, we recognize the change of the seasons by the changes in color.

The length of day and temperature are the chief factors that influence when leaves start to change. The combination of shortening days and cooler nights triggers changes in the cells between the leaf and stem, eventually depriving the leaf of water and nutrients.

Leaves get their green color from chlorophyll, the predominate pigment in the leaf. When the chlorophyll dies due to the lack of water and nutrients, other pigments, previously masked by the chlorophyll, become visible.

Pigments called carotenoids and xanthophylls give leaves yellowish and brownish colors. The reds in sumacs and maples are caused by anthocycyanin, a pigment produced by leaves with a high sugar content.

Abnormally dry weather will reduce the color intensity of these leaves because the parched leaves do not produce enough sugar.

Thus, a number of natural processes produce the colorful displays throughout the countryside. In too short time, however, the leaves will begin to fall, signaling the approach of winter.