Leaves change color for several reasons
PRATT — Fall is the season of color in Kansas, and 2010 has been a good year for those who love the changing hues of autumn leaves, as mild temperatures have kept leaves clinging to branches longer than normal. Autumn weather produces some of the year's clearest skies and most pleasant temperatures, and changing foliage invites the sight-seer to the outdoor's grandest festival.

Leaves change color for several reasons as summer yields to impending winter. First, unknown to many people, leaves’ true colors are often reddish. This can be seen when leaves first break dormancy in spring, and they appear in pastel reds and purples. Very quickly, green chlorophyll develops to help the leaves produce food, overshadowing the brighter colors. As leaf activity subsides in fall, the chlorophyll breaks down and becomes colorless. This allows the underlying colors to show again.

Even more important are chemical changes that act to color the leaves. As the amount of daylight grows shorter each day, physical changes take place to allow the old leaves to drop. The base of each leaf forms an abscission, or shedding, layer of cells, which effectively plugs the pipelines that carry food and water between leaf and tree. On warm days, sugar continues to be produced in the leaf but cannot be transported to the roots. As sugar levels build, chemical changes occur to create vivid reds and yellows. This continues until the leaves die and drop.

Some species can be counted on for spectacular color each year. Statewide, look for vivid reds in smooth sumac and poison ivy. Sugar maples and some oaks also produce crimson reds. Maples are known for deep orange, and other oaks and hickories turn a burnished gold. Cottonwoods can add a vibrant yellow to the landscape wherever they're found.

Rainfall often affects autumn's show. In dry years, colors are often dull and lifeless, with leaves turning brown while still on the trees. (Cottonwoods in southcentral Kansas, for example, are not as brightly yellow this year, likely due to lack of rainfall.) In wet years, leaves may continue to grow late into the season so that persistent chlorophyll masks much of the autumn color. Best are years of average weather conditions when many days of warm sun are followed by cool nights.

However intense, autumn's show of color is usually nature’s most brilliant feature, and many nature lovers take advantage of the outdoors at this special time.