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Wisconsin’s Fall Colors


Posted: 10:43AM September 5th, 2017 | Comments

Every year when the first leaves begin to change and mark the approach of autumn I get so excited. Autumn is such a beautiful time, especially here in Wisconsin. We have such a huge variety of trees, the colors get so bright and the diversity is enchanting.


This year while noticing a small tree that was already nearly completely red, I realized I didn’t really know the science behind why leaves change. Some years I feel like the leaves change and fall within a week, and other years it seems like they stick around longer. I did some research to see if there’s a scientific explanation behind these observations, and what kind of fall leaves we can expect this year.


Leaves are full of different molecules that have various pigments. For spring and summer only green is visible because green is the color the molecule chlorophyll emits. Throughout this time, the sun depletes the chlorophyll and in response the leaves continually replenish it to make the tree’s food through photosynthesis. Trees depend on the sunlight for energy, so during fall when the days grow shorter the chlorophyll stops replenishing. In the absence of the green pigment, the yellow and orange pigments are visible. Later, when the leaves begin to seal off for the winter, red and purple pigments appear. Finally, as the leaves fall and decompose, the brown tannins become dominant.


Although the primary reason the leaves change color is the decreasing sunlight, the prior year’s weather does have an affect. This year will be Wisconsin’s wettest yet in 123 years of weather recording. The average precipitation this year reached 25.25 inches as of July 31st, which is 7.14 inches above the regular yearly average. So what can we expect from the abnormal amount of precipitation this year? According to the U.S. National Arboretum, a wet spring season is helpful in jump-starting the photosynthesis process, but a sunnier summer than we’ve had is best for a long and colorful fall. Very sunny days and cool (but not freezing) nights initiate the chlorophyll degradation process sooner, but we’ve had a lot of cloudy and stormy days that have likely left the trees with excess chlorophyll.


If these assumptions are correct, we’ll have a short window of time to view the fall colors in Wisconsin this year. I’m going to let that knowledge inspire me to make the most of it! Even if this year’s fall is short, hiking trips to the Driftless area- or even just to the lakefront here in Madison- will be beautiful.


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