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The science behind the beauty of Western Montana's autumn leaves

Posted at 6:39 PM, Oct 01, 2019
and last updated 2019-10-02 16:17:28-04

MISSOULA — It happens every fall -- the changing of leaf colors ushering in autumn days.

There is, of course, a science behind it -- and Montana State University Extension Forester, Peter Kolb knows tree leaves inside and out.

“The shorter the day length, the less sunlight triggers a hormonal response where they start to recycle all the chlorophyll,” Kolb said. “Trees that are physiologically active freeze. The water in the cells turn to ice which expands, and it causes damage like frostbite in a human.”

Frostbite in a human is never fun, but you must admit, the similar effect on leaves… we like that. While the length of days is the catalyst for the change, weather plays a role in the brilliance of color you see, and the length of time you get that color.

“If a tree goes into drought stress, it will just let it’s leaves sense -- and those just turn yellow and brown,” Kolb said. “When we have a nice cool, wet summer like this year, we should have good colors.”

It stands to reason that this year’s colors should be better than the last two, but with one exception. A deep cold snap featuring lows below 27 for a few hours, could have those colors brown quickly.

But here’s some good news: You have a hand in the fall color of your trees.

“Making sure they’re well-watered through the summer. Good micronutrients, magnesium, phosphorous, potassium, and all are important in have a better tree physiology that tends to bring out more brilliant colors,” Kolb said.

Given all the factors laid out by Kolb, he says it also comes down to luck, and we’re pretty lucky. He says Missoula has the best fall colors in the state. And there is one area in particular that shines brighter than the others.

“The older section of Missoula around campus has the most brilliant colors because there is a really big and diverse species mix,” Kolb said.

So get out and enjoy the beauty around you – Those brilliant reds, yellows, and oranges will be brown before you know it.