The autumn equinox has officially arrived, marking the beginning of fall and the showcasing of the early stages of tree leaf color changes throughout Wisconsin.
It can be a magical time of year, as leaves burst with a spectrum of brilliant colors. Peak season is still a couple weeks away for most of the state, still leaving plenty of time for leaf-peeping excursions, whether Up North or right here in and around Milwaukee.
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A cold start to September caused some to speculate on an early color turn, but temperatures have been well above normal, with plenty of sunshine, since then.
“Things haven’t even really begun here yet, and not even that much in the far north,” said Dan Blazer, a certified arborist with Davey Tree Service in Milwaukee. “You’ll see some red maples and sugar maples start showing a little bit of red Up North. But here in Southeastern Wisconsin, if we keep getting rain and the temperatures stay in the 60s and 70s, it’s not going to happen for another three weeks or so.”
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Travel Wisconsin’s extensive fall color report shows the majority of the state in the early stages of transformation to this point, with the exception of some areas in northern Wisconsin.
Forest County, for example, has reported a 60% color change as of Thursday, with peak foliage expected in the first week of October. Medford, in the north central Taylor County, is at 50%. Some parts of central Wisconsin are beginning to show more significant color, with southern Wisconsin, typically the last to change, mostly showing little or no change. Peak season for Milwaukee and elsewhere in southern Wisconsin is expected in the third or fourth weeks of October.
The Science of Fall Color
As anticipation grows for checking out the fall colors, there’s a process going on beneath the surface that transforms trees into a colorful palette. “Different species of trees also have different fall colors due to different proportions of organic chemicals,” Blazer said.
At the root of the transformation is chlorophyll, the green pigment in tree leaves responsible for photosynthesis, the process of converting sunlight, water and carbon dioxide into sugars that fuel a tree’s growth, he explained.
In the fall, decreasing sunlight and cooler temperatures cause trees to stop producing chlorophyll, leading to the breakdown of the pigment while revealing other colors, Blazer said. “In response to longer nights and extended periods without sunshine, the chlorophyll starts to break down,” he said.
The process leaves behind carotenoids, the yellow and orange pigments in tree leaves that are always present but only become visible when chlorophyll breaks down, Blazer explained.
“When things break down even further, there are pigments called anthocyanins, which produce more of the reds, blues and purples, the extreme vibrant colors,” he said.
Once those pigments fade, what remains are the dead leaves, which tend to be brown due to tannins, Blazer added.
What Affects Peak Color?
A variety of factors contribute to timing of the color transformation.
“First and foremost is sunshine,” he said. “The farther north latitude means that there is less sunshine. Just like how the trees leaf out later in the north and everything is slower to come in the spring, they also tend to be the first to go in the fall. It’s related mostly to sunshine, but can be temperature-related, too.”
Drought conditions or excessive moisture can alter the process. Very dry weather often pushes trees to turn earlier, Blazer said. “The process will happen quicker and be less vibrant,” he said. “There have been a couple years recently when leaves were not that stunning due to drought.”
Adequate moisture and seasonal temperatures tend to be ideal.
“What you want is moist, well-drained soil. That’s when you’ll get the really nice colors,” Blazer said, adding that considerable moisture is less likely to dampen fall colors than drought. “It’s pretty hard to have too much moisture in a hardwood forest where sugar maples and other trees thrive,” he said. “They have, by nature, well-drained soil.”
Another factor is the species of trees in a given region.
“Poplars, which include aspens, and ash trees turn to fall colors pretty quickly. Honey locust trees are turning yellow already, even here,” Blazer said. “Up North, there’s a lot of aspens mixed with evergreens like conifer, fir and spruce trees. That green and gold mix is so pretty.”
Once leaves begin changing, the colors will last just two to three weeks, Blazer said.
“Generally, it’s not very long,” he said. “It can depend on moisture and not having high-wind events. It’ll usually end with a good rain storm and high winds.”
Keep an Eye on Your Own Yard, Too
Although much of the talk around here this time of year centers on planning a trip to check out the colors, Blazer also has advice for those wanting to enjoy the trees on their own property.
“If you notice a yard tree that you care about on your own property and it goes into fall color early or doesn’t get fall colors at all, it might be due to nutrient-deficient urban soil,” he said. “When trees are stressed, they will go into fall color really early or they’ll drop leaves early. The trees essentially shut down. Going into dormancy is a protection mode. They are trying to conserve energy.”
Proper mulching and fertilizing are ways to counteract the issue.
“If that doesn’t work, have an arborist come out and take a look,” Blazer said.
