Opening week of autumn delivers peek time for peak fall colors

MARQUETTE, Mich. (WLUC) - Fall season has officially arrived, shining on through to the Upper Peninsula. And with it, the familiar autumn hues have begun spreading amongst the leaves.

Dr. Carsten Külheim, Associate Professor at Michigan Tech’s Forest Resources & Environmental Science Department said we’re on track overall in nearing peak colors -- but just may take a little longer in some spots even around the Keweenaw.

“Up here in Houghton and Hancock, I think we’re probably about a week away from peak season," he said.

Dr. Külheim pointed out a dry late spring and early summer in delaying the color change for shallow-rooted trees like poplars and birches.

Weather conditions are critical in the process for fall colors to blossom: sufficient moisture in the soil and a good dose of clear and cool (but not frosty) nights.

With longer evenings and less sun to convert into energy (photosynthesis process), the trees prepare for an almost hibernation state before the winter.

Dr. Külheim explained the color-producing cycle.

“In fall what happens is that the tree wants to recycle some of the nutrients that are in there ... they start to break down chlorophyll. Chlorophyll contains nitrogen and we all know that if we want to fertilize plants we add nitrogen to them. That nitrogen is brought back into the tree, all the way down to the roots where it is stored over winter. Once that green color is gone (from chlorophyll breakdown) other colors come forth,” he said.

And that leaves for the other pigments to glow. Carotenoids produce the yellow and orange shades found on sugar maple leaves. And the bright reds to purples produced by anthocyanins -- like on grapes and cherries.

“And a lot of the leaves once all the nutrients are taken back into the tree, the leaf dies and becomes litter for us which is also an important nutrient for recycling," said Dr. Külheim.

In turn he explained, the remaining nutrients on the forest floor work back into the soil and end up serving as fertilizer for nearby flora -- beginning the cycle once again in time for next fall.

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