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We’re accustomed to short springs on the Palouse, but now it appears that fall has sped by as well. In case you missed it, when the skies finally cleared after Friday’s rainstorm many of the trees were bare.
 
“The maples in one day dropped virtually everything,” said Charles Cody, plant growth manager for the Washington State University School of Biological Sciences. Already dead from a hard freeze two weeks earlier, the leaves had no staying power.
 
Some trees might continue to hold onto their leaves for quite a while, Cody said, because it all depends on the tree’s particular abscission layer, or the cells that govern when the leaves detach from twigs. “Oak leaves are going to fall as normal,” he said, “but they’re not going to color up as usual.”

This precipitous leaf drop comes on the heels of a disappointing color season. WSU Regents Professor Gerald Edwards said Jack Frost’s early visit to the Palouse, setting record low temperatures on Oct. 10-12, effectively put a kibosh on any possibility of spectacular fall colors. Though a few trees escaped, many had their leaves freeze-dry, die and turn greenish-brown on the branches.
 
In a sense, heading into the winter with dead leaves on the tree is like sending a bear off to hibernate before he has eaten his fill: Those dead leaves mean trees are fasting when they should be feasting in preparation for a long winter.

“Nature can be cruel to plants,” Edwards told his students in a recent lecture on photosynthesis at the University of Idaho. The leaves, he said, had no time to show their brilliant colors or to export their nutrients to support the trees’ growth next spring. Typically, he said, fall colors begin to emerge as the days become shorter and the temperatures cool. It’s a genetically controlled, biological process that requires living tissue, intact cells and enzymes that are responsible for metabolism.
 
Edwards said that inside leaves there are two different pigments - chlorophylls and carotenoids - which are critical to photosynthesis. The chlorophylls harvest solar energy for photosynthesis during the growing season and produce the green color that dominates throughout spring and summer. But, once the growing season is over, the chlorophylls disappear, unmasking the carotenoids, which are then visible as yellow or orange.

For more information, contact Charles Cody at 509-335-4064 or ccody@wsu.edu and Gerald Edwards at 509-335-2539 or edwardsg@wsu.edu.

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