It looks like a good fall for leaf color

Oct 30th, 2008 | By | Category: Campus News, October 30, 2008

It’s going to be easy to fall in love with the colors of autumn this year. Gorgeous reds, yellows, oranges and burgundies will abound in the leaves of deciduous trees before they tumble to the ground. Weather plays a big role in how vivid the fall leaves are, and this has been a good year for the development of color, said Chip Murrow, UNL community forester assistant.

While the image of an elfish Jack Frost painting the leaves with frost is charming, that’s folklore, not fact. If there is a quick freeze or early frost, leaves lose their color rapidly and turn brown instead of bold. The ideal weather for maximum color is warm to cooler days followed by cooler, but above freezing, temperatures at night, with no or little rain, and that’s been the weather pattern so far this fall.

fall leaves
FALL COLOR – The Love Library cupola is framed by the yellowing leaves of a shagbark hickory in the Cather Gardens. Photo by Troy Fedderson/University Communications.

“In the Midwest, we’re lucky to have fall color from a variety of trees. Different species produce different colors,” Murrow said.

One of Murrow’s favorites is the sugar maple. Its leaves turn from a golden yellow to orange to red. Red maples, red oaks and sumac produce reddish hues while native birches and cottonwoods turn yellow. Not all species provide such gorgeous hues. Elms, for example, mostly turn brown.

Here’s the science behind that beauty: A leaf’s chlorophyll has to be made every day. Chlorophyll is essential for photosynthesis, which is the chemical reaction that enables plants to use sunlight to manufacture sugars for their food. These sugars are stored during winter.

Cooler days and longer, cooler nights result in decreased chlorophyll, which triggers leaf senescence, the process of leaf aging and death. As chlorophyll production slows, the color pigments become visible. Carotenoid pigments provide the shades of yellow. Some species also have anthocyanins, which mix with sugar in the leaves, to produce reddish and purplish hues.

There are tradeoffs for all that beauty. Shortly after leaves reach their peak color, they fall to earth, ready for the next – and much less enjoyable – aspect of fall leaves, raking.

— Story by Linda Ulrich, IANR News Service

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