Serving Northern St. Louis County, Minnesota

Weather plays its part in fall’s color change

Marshall Helmberger
Posted 10/4/18

REGIONAL— If you’re one of those folks, like me, who tracks the changing of the seasons here in the North Country, you have probably noticed that our fall color seems a bit later than usual. As …

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Weather plays its part in fall’s color change

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REGIONAL— If you’re one of those folks, like me, who tracks the changing of the seasons here in the North Country, you have probably noticed that our fall color seems a bit later than usual. As most residents of our region know, we really have two color seasons here— the fiery oranges and reds of the red maple, which tend to peak about the fourth week of September, and the golds of the aspen and tamarack, which generally peak around Oct. 10.

To understand this process, first recognize what causes the change in leaf color. Throughout the growing season, the green chlorophyll dominates the chemical makeup in leaves, which is why leaves appear green to us. But as the tree begins to shut down for the season, the chlorophyll breaks down and other chemicals, like carotenoids (which appear orange) and anthocyanins (appear red), begin to show through.

While color change is typically driven mostly by daylength, other factors can affect the exact timing and brilliance of the color change, and it seems they’ve been mostly working against us this year. The month of August is actually an important period for determining the kinds of colors we’ll see come September, and the dry conditions we experienced in August this year almost certainly reduced the production of anthocyanins, which are produced late in the season in part to better prepare deciduous trees for winter. Any time trees are water stressed, they tend to produce less of this chemical compound, so our August dry spell is likely responsible for the limited amount of the brilliant reds we’ve seen this season from the maples.

And our gloomy weather in the last half of September hasn’t helped. Mild, sunny days and cool nights produce the best color change, but the cool, wet, and persistently cloudy weather we experienced in the second half of September seems to have slowed the changing of the leaves. Even so, there might be a silver lining. I keep waiting for that spectacular year when our two colors seasons merge into one, and the entire forest is ablaze all at once.

Will this be the year? It’s starting to look that way!

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