Botanists, weather folks know a lot about foliage; but still hard to predict

Leaves may be turning to full color a bit earlier this year.

Leaves changing color before they flutter to the ground ahead of winter is something annually anticipated in Indiana, and there are some indications the foliage color change may be a bit ahead of the normal schedule this year.

Touring the countryside viewing leaves is something anticipated by many, including promoters of fall festivals and many shop owners.

Leaves have started turning color this fall, and in some areas may be close to their peak of brilliant colors. In Indiana, the peak of color usually spreads from north to south, and it usually is best in the south about the third week of October.

Apparently, it is difficult to predict the change. There is a lot known about what causes color in the leaves, but predicting its intensity isn’t easy. 

This summer we had an abundance of rain, followed by very dry conditions in most areas the past couple months. Some botanists believe the trees are still suffering somewhat from dry conditions the past several years, even though we had a lot of rain this summer.

       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."

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 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.

A website called Chiff.com: (www.chiff.com/travel/indiana-foliage.htm) contains Indiana fall festival and foliage information, and includes links to several leaf webcams. They are located at Notre Dame University, Spring Mill State Park, and Brown County.

Whether or not you care about anthocyanins or carotenoids, there should still be plenty of beauty to be found yet this weekend.