GREEN BAY, Wis. (WFRV) – The fall foliage is a beautiful display that attracts a large amount of activity to the region when the leaves are in peak color. What I sought to find out is how drought conditions affect fall foliage.

To accomplish that task, I caught up with Karen Stahlheber, an associate professor of Biology at the University of Wisconsin Green Bay, to understand the science behind this phenomenon just a bit better.

“Fall really starts when the days start getting shorter at this time of year and that sends a signal to all the plants to start slowing down and instead of producing more of the green pigment that they need to make food, they start to break it down instead. So they are breaking down all the green pigments to store those nutrients for the winter and when the green color starts to break down, we start to see other pigments that have been there all along like the yellows and the brown pigments.”, Stahlheber says.

Green Pigments are also called chlorophyll, which plants recycle as they are rich in Nitrogen. These yellow and brown pigments are called accessory pigments, which are the ones plants don’t recycle when the green pigments begin to break down. There is one remaining pigment that is important and that is the red pigment. This one is not available year-round and can only be produced during the fall. Stahlhaber says certain weather conditions favor the production of this red pigment.

“So when there are bright, sunny days in the fall, plants have enough energy to make a lot of that red pigment and those cool nights encourage it to be brightly colored. So warmer nights can lead to less bright red coloration and drier conditions also can affect the way we see the colors.”

The spring and summer of 2023 was very dry weather-wise across our area, so how could those conditions affect this year’s fall foliage:

“We had a really dry spring and summer and sometimes that can be very stressful for plants and in cases where the drought is very stressful, they might start turning colors earlier up to a few weeks earlier than normal… it can also lead to the colors not being as bright because the leaves might turn brown and fall before they really have a chance to turn. And in other cases when the drought is less severe, it can actually make the fall foliage happen slower. The reason why that happens is not totally clear but it might be not having food all summer will slow the plants down just enough that it delays the onset of the foliage.”

Stahalheber says some species of trees drop their leaves earlier than others, which is why some regions see an accelerated peak period compared to some surrounding communities. So enjoy the fall season before the next season knocks on our door.