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Sunday, October 14, 2012

Predicting fall foliage is more a guess than scientific analysis

Predicting fall foliage brilliance is pretty much a guess.

        It seems to be really difficult to predict the impact summer weather, including drought, has on fall foliage.
Many forecasters projected the drought would mostly eliminate fall tree color to the disappointment of many who enjoy it. Touring the countryside viewing leaves is something anticipated by many, including promoters of fall festivals and many shop owners.
It seems there is a lot known about what causes color in the leaves, but predicting its intensity isn’t easy.
       Abby van den Berg, University of Vermont plant biologist, who has done research on leaf colors, said some data suggest a small amount of physiological stress can result in more brilliant colors.
"The real bottom line is that there's no great way to predict these things," she said. "It's pretty much impossible, especially over a large scale."
The prognosticators predicting less color this year may have been partially right, but there is more color in areas I have visited, than I anticipated. There are more reds and oranges than forecast and the peak of color should still be ahead.
The extreme dry conditions in most areas during early summer through July may have impacted the number of leaves to view more than the color. And in addition to problems caused by the drought, some trees dropped their leaves due to insect infestations.
Drought conditions cause trees to switch to survival mode because of the latest dry spell. Some lose their leaves before they change to the familiar red, yellow or orange, according to nature experts.
"For the trees' well-being, it's do or die," said Jim Eagleman, an interpretive naturalist. "The reaction to drought is they drop leaves to conserve water."
 This was the second straight summer with drought conditions.
Despite the dry conditions, Eagleman said there still will be a plenty of trees healthy enough to please nature lovers.
"We've got so many trees with so many leaves that you're bound to have good color in a lot of them, even though we're under stressful conditions," Eagleman added.
This spring there was plenty of rain, and trees were loaded with healthy, green leaves. They are green because they contain chlorophyll. 
According to one agriculture department website, there is so much chlorophyll in an active leaf that the green masks or overpowers other pigment colors. Light regulates chlorophyll production, so as autumn days grow shorter, less chlorophyll is produced. 
The decomposition rate of chlorophyll remains constant, so the green color starts to fade from leaves.
While that is happening, increasing sugar concentrations cause increased production of anthocyanin pigments. Leaves containing primarily anthocyanins will appear red. 
Another type of pigment, carotenoids are found in some leaves. Carotenoid production is not dependent on light, so levels aren't diminished by shorter days. Carotenoids can be orange, yellow, or red, but most of these pigments found in leaves are yellow. Leaves with good amounts of both anthocyanins and carotenoids will appear orange.
Temperature affects the rate of chemical reactions, including those in leaves, so it plays a part in leaf color. However, it's mainly light levels that are responsible for fall foliage colors. Sunny autumn days are needed for the brightest color displays. Overcast days will lead to more yellows and browns.
Whether or not you care about anthocyanins or carotenoids, there should still be plenty of beauty to be found yet this weekend.
A live leaf camera at four Indiana sites can be found on the internet

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