Leaf Peepers, Rejoice! What science tells us about fall colors

Photo by Len Villano.

Fall is all about getting cozy, and there’s nothing more cozy than seeing the landscape painted with vibrant autumn reds, oranges and yellows. (Well, except maybe when you look out your window late at night in the winter and see everything blanketed in a fresh snowfall, illuminated only by a dim streetlight, but let’s not get ahead of ourselves.)

Door County was named the Best Destination for Fall Foliage in the 2019 USA TODAY 10 Best Readers’ Choice travel award contest, and it’s no wonder why: The colors are often spectacular. But, there are many factors that go into what makes the colors really pop, and analyzing the conditions of late summer can illuminate what to expect as we enter October.

How leaves change color

“There are three pigments in leaves that create the spectrum of colors on trees,” Jackson Parr wrote in a 2016 Peninsula Pulse article. “Chlorophyll keeps leaves looking green through the summer as it converts sunlight from long summer days into food for the tree. Although weather plays a big part in the intensity and duration of the fall colors, leaves stop producing chlorophyll at nearly the exact same time every year since the process is linked to the length of the days and the intensity of sunlight.

Without chlorophyll in the picture, carotenoids (yellows, oranges and browns) and anthocyanins (reds, purples and blues) begin showing their true colors.”

Although we might see the colors as a burst of lively vibrancy, “the vivid colors foretell the impending death of the leaves,” said Coggin Heeringa, Crossroads at Big Creek’s program director and naturalist.

“A leaf begins to die when a specialized set of cells called the abscission layer forms across the base of its stem. This layer cuts off the flow of water and nutrients to the leaf. Chlorophyll is used up with exposure to light. Without water and nutrients, no new green bodies can be formed. Without the masking effect of the green chlorophyll, yellow pigments are revealed.”

What are the current circumstances?

Not only can science explain the mechanisms by which the change happens, but it can also give us a great deal of insight into when it will happen, what it may look like and how long it will last.

“Drought during the growing season means colors turn early and don’t last,” said DNR silviculturist Colleen Matula. “Severe drought stress may cause trees to skip the colors entirely.”

Although some areas in Wisconsin have been going through abnormal or severe drought, Door County has seen adequate moisture this year. But moisture isn’t the only factor deciding the fall colors’ fate. Areas around Lake Michigan are affected by the temperature of the lake water, and right now it’s like a “big, warm bathtub,” as Matula described it.

“When it’s warmer, especially in the evening,” she said, “it puts off the color change. It doesn’t signal the tree to slow chlorophyll production.”

When will the colors pop, and what will they look like?

So what should we expect this year? Warmer temperatures can affect which colors we see, the vibrancy of those colors and the timing of peak color. 

With the recent weather, Matula predicts that we may see a more muted yellow and orange palette on the trees because brilliant colors – especially reds, purples and blues – need cool nights. 

Peak colors should happen slightly later than normal, too. 

“Right now, we’re between 20% and 30% [of the peak],” Matula said. “Maybe the second week of October – that’s my prediction.”