Some Wisconsin trees are changing color early this year. Here's why.

As fall begins in Wisconsin, you might be seeing some trees changing colors a bit earlier than usual.

This is largely due to the drought which has caused stress on many trees in the state, triggering them to accelerate their aging process.

The Journal Sentinel spoke with Wisconsin Department of Natural Resources Forest Ecologist and Silviculturist Brad Hutnik to learn more about how this will affect fall colors. Here's what you need to know.

What causes tree stress?

Hutnik said that tree stress occurs in some form every year. In most years though, you'll see it in trees near lakes or rivers suffering from tree stress because of too much water. This year is the opposite. Because of drought conditions for most of the summer, many trees in the state have too little water which could impact the fall colors.

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"Colors will still be beautiful," Hutnik said. "But it will be different in different places depending upon the degree of stress. If we're missing rain then we could have a shorter season. Ironically, we also could see more vivid colors depending upon the trees you have on those sites."

How do leaves change color?

Leaves change color via chlorophyll, the green pigment present in all green plants and responsible for the absorption of light to provide energy for photosynthesis, according to Hutnik, . When trees shut down for the year as a result of days start becoming shorter, what's called an "excision layer" forms between the leaf and the branch. This causes the chlorophyll to become less visible and the other pigments in the leaf become visible. These pigments are called carotenoids, which are yellow, and anthocyanins, which are red.

So, how does tree stress affect fall colors?

If there is tree stress caused by the drought, how it will affect the colors will depend on the tree species, Hutnik said.

"There's always a red maple somewhere that's changing earlier than the rest, but this year might be different in some places because of the stress," Hutnik said. "Aspens in the north or poplar trees turn yellow. Depending upon the drought stress, it can impact those pigments as well. A good example might be if you were to see some of the anthocyanin being impacted. The colors should be the same, but how bright or dull they are could be changed. Each species will handle it differently."

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Hutnik added that if places are missing a lot of rain, the fall colors season could be a lot shorter this fall. This is because a drought might accelerate the aging process in the leaves whereas in moist condition, the leaves are able to hang on a bit longer.

Does this mean all leaf colors will be duller this year?

Ironically, in some cases, some trees might be more vivid than in other years because of the different type of stress and a tree's ability to handle stress. Oaks, for example, are able to handle drought conditions better than say a maple tree.

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"With the moisture stress, the season might seem longer because the dry sites might lose their leaves earlier, but those slightly more moisture rich sites might hold theirs longer," Hutnik said. "They might look like they're holding on longer even though they're holding it maybe just the normal time. You'll see some differences across the landscape in where the colors occur."

Will this be the same all over Wisconsin?

It's not totally predictable but most places should see some form of tree stress from the drought, Hutnik said. The places that might see trees hold up a bit longer and see more normal fall color changes are trees near rivers and lakes and certain places that weren't affected by drought as badly in Wisconsin.

Is there any advice for people in Milwaukee looking for fall colors this year?

"I think one place that people, especially in the Milwaukee area, might want to go walk around in is the Forest Exploration Center in Wauwatosa," Hutnik said. "There's a really cool set of trails there and when the leaves change, it's really good. It has a lot of sugar maples and oaks."

How can I track fall colors in Wisconsin?

The best place to track fall colors in the Badger State is Travel Wisconsin's fall color report, which has an interactive map that shows that status of the changes around the state. You can find that map on travelwisconsin.com.

Drew Dawson can be reached at ddawson@jrn.com or 262-289-1324.