Why do leaves change? Forest ecologist shares science behind fall colors

LISLE, Ill. (WLS) -- The leaves are just starting to change. But how vibrant will the fall colors be this fall season?

Meteorologist Larry Mowry went to the Morton Arboretum to talk to an expert. It's a special time of year when our trees prepare for the season to come.

BEHIND THE LENS | Fall colors at Morton Arboretum

Many come to the Morton Arboretum to take in the changing colors. But how vibrant will the fall colors be this fall season?

"It's a great time to wander around," said Dr. Christy Rollinson, a forest ecologist with the Morton Arboretum. "This year has been a great growing year for most of the trees, so they are coming into fall with big green leaves that they take their time getting that energy out which leads to that vibrant color that I think we are in store for this year."

Many come to the Morton Arboretum to take in the changing colors.

"The color of the leaves, how vibrant they are, can tell you a lot about the health of the tree," Rollinson said. "If your tree is turning color before other similar trees in the area. Or if the color is kinda yellow and not that great. That could be a clue something is wrong with the tree."

So what causes the leaves to change? Is it less daylight? Or colder nights?

"There's definitely some trigger with the daylight, but it's the cold that really speeds it along," Rollinson said.

But why do leaves change color?

"So the changing of the color is actually the removal of green," Rollinson explained. "It's breaking down the green, the chlorophyll of the tree. And when it does that it reveals these colors, bright yellows, that are always there but hidden from the green."

The trees are removing that energy from the leaves and preparing for winter. But there's still much we don't know about this process.

"We still haven't been able to link the vibrancy of color or timing to how it sets up the tree for next year," Rollinson said.

Scientists like Dr. Rollinson continue to study trees year-round to get some answers. But now is the time to enjoy the show the trees put on.

"Get out and explore your neighborhood," Rollinson said. "It's a great opportunity to walk down your block or to the nearest park to see what is going on."

If you have a tree that you think is struggling or doesn't look right this fall, the Morton Arboretum has a plant clinic where you can call and get advice. That phone number is 630-719-2424 or email plantclinic@mortonarb.org