Leaf color should be extra vibrant this fall
October 31, 2010
LINCOLN, Neb. – Sunny days and cool nights mean it’s shaping up to be a good fall for leaf color.
While shorter day length, not frost or cold temperatures, is the main reason trees lose their leaves each fall, the sunny days and cold nights are helping to give leaves the best color for fall, said Dennis Adams, forester in the Nebraska Forest Service at the University of Nebraska-Lincoln.
Ample summer moisture in many parts of the state also is helping make leaves more vibrant. Heavy spring and summer rains also made for ample acorns on some oaks, especially the pin oak.
While weather does play a role, leaves really change colors because of chemical changes that take place in the leaves.
There are pigments in leaves all the time, Adams said.
Green is dominant during the growing season. As the season progresses, leaves deteriorate and some of the other pigments, such as carotene or xanthophyll for yellows and oranges and anthocyanins for the reds and purples, start to dominate.
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Adams said cool nights slow down chlorophyll synthesis and accelerate the breakdown of the green pigments. This allows the yellow colors of the carotene and xanthophyll to stand out. Bright, sunny days increase the rate of photosynthesis and result in excess sugars to produce anthocyanins or red pigments. Warm, rainy autumns generally produce dull colors.
He said leaf change does vary from year to year.
Often, the fall frost is credited with leaf color change, but frost actually deserves little credit. In addition, freezing temperatures may kill leaf tissues and prevent any colors from forming, Adams said.
Leaf color change varies by species. Ash trees started turning yellow in September. However, oaks won’t start to really turn until late October and November.
It also depends on the area of the state and the weather there this summer, he said.
Adams said early yellow leaf color is typical for cottonwood, green ash and honey locust. He said some hard maples also are starting to turn right now, including sugar maple, which often exhibits brilliant red and orange foliage. He said peak time for leaf color change will be mid-October to mid-November.