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Archive for Thursday, October 19, 2006

The science of fall color

October 19, 2006

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Winter's approach in Kansas is signaled by dropping temperatures, strong winds and the changing color of the landscape. One day it's green, and the next sunrise shows a combination of crimson, rust, yellow and gold. This natural process actually started June 21 as the days, ever so slowly, began getting shorter.

The science behind this phenomenon falls into three categories: colored pigments, weather effects and tree species.

The key factor is color pigments. Chlorophyll gives the leaves their green color and enables the plant to manufacture food through photosynthesis. In addition, present year-round, is the pigment carotene. It is masked by the green chlorophyll and produces the yellow, orange and brown colors. These carotenoids are also present in corn, carrots and bananas. The pigment anthocyanin is responsible for the red, orange and bronze, just as it is in cranberries, red apples, grapes, blueberries, cherries and strawberries. This leaf pigment is produced in the late summer or early fall in response to environmental cues.

As the days get shorter, growth slows, and the chlorophyll production decreases. This allows the yellow, brown and orange carotenoid pigment to show. Hence the first fall color. The anthocyanin pigment now starts to develop in some trees. Development of the anthocyanin pigment is sunlight dependent. This provides us with the color variations even on the same tree.

A succession of warm, sunny days and cool, crisp (but not freezing) nights brings about the most spectacular color displays. The amount of moisture in the soil, either now or in the spring, only changes the timing of the show by a few weeks, not its intensity. A warm fall will lower the intensity of the color. Cloud covered skies block the sun for more subdued colors. The innumerable climatic combinations of temperature, cloud cover and moisture - both now and in the spring - assure us that no two autumns will be exactly alike. The first hard frost marks the end of the show, and brown becomes the dominate color for all leaves.

Yellow color is characteristic of birch, hickory, ash, black oak, beech, poplar and willow. Red or scarlet leaves are found on silver or red maple, dogwood, sweet gum, white or red oak and sumac. Cultivars within the species may have slightly different colorations. The fall color in New England is certainly stronger than that in Kansas, owing to large, pure stands of the same species, all turning color at the same time. Likewise with the large aspen groves to our west.

Kansas supports a large and intermingled variety of trees with various colors and times of change. Our fall color is set off by the one lone specimen, seemingly highlighted, by all others. We need not travel far for the beauty of fall.

- Stan Ring is the horticulture program assistant at K-State Research and ExtensionDouglas County. He can be reached at 843-7058 or Sring1@oznet.ksu.edu.

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