Before Louisville’s sugar maples shed their leaves, the foliage does its best interpretation of a sunset, turning shades of tangerine and crimson.
These maples are among the city’s most brilliant fall colors and also among the most common, but that will change as the planet continues to warm, said Margaret Carreiro, an associate professor at the University of Louisville who studies urban and suburban ecology.
The sugar maple is an example of a tree that will struggle to adapt to Kentucky’s warming climate. Fully grown and landscaped trees will continue to survive, but seedlings and saplings will have a difficult time reaching maturity on their own.
Carreiro said by the end of the century, the sugar maple’s brilliant fall colors will fade from the Commonwealth’s forests. The trees will retreat north where the climate is more suitable.
That’s because climate change will make Kentucky’s weather more unpredictable, with more droughts and more severe storms.
“[Sugar maples] will be leaving the landscape by the end of the century, here in Kentucky for sure, no matter whether it is drought and warmth or warmth and the same rain,” Carreiro said.
Other trees, like the American beech will see similar challenges. At the same time, plants that do well in warmer climates like the southern magnolia will become more common.
Not everything related to a changing climate is bad for trees though. Warming temperatures will extend growing seasons, giving trees more time to soak in the sunshine before dropping their leaves.
Arborist Chris O’Bryan says he likes to think of trees as having a rhythm. Each tree and species may choose to shed its leaves at its own moment. But it’s all of these decisions together that make the symphony of fall foliage.
“So it’s a part of this other rhythm that’s happening now,” O’Bryan said. “So we came out of the living rhythm and now we’re moving into the decay rhythm.”
For trees, the rhythm of autumn is driven by the seasons that come before it. During dry years, the leaves fall sooner, but this year’s wet spring and late summer helped trees stay greener, longer.
As fall comes, trees begin to pull the remaining energy from their leaves to store in their roots until spring arrives. As the chlorophyll breaks down, the greens disappear — leaving behind the yellows and oranges.
But other pigments can appear too. Chemical changes in the leaves can induce vivid-lipstick reds and wine-soaked purples.
Look up close and you’ll see the leaves are a little beat up. They’ve survived storms — as well as bugs and fungal infections that leave behind pockmarks and spots.
“I always like looking at the end of the year, because they always remind me of life in general, it can be harsh at times,” O’Bryan said.
That’s also one of the problems of an extended growing season, it’s more time for pests to breed and attack trees. Bugs like spider mites are pervasive on spruce and hemlocks in urban forests, in part because of the warmer, drier conditions.
O’Bryan said that homeowners that want to help their own trees can start by keeping around some of those fallen leaves.
“Life always has death, they go hand in hand,” he said. “I mean life is beautiful and wonderful and people don’t talk about when it’s the thing on the ground, decay, but that’s super important too.”
All those falling leaves break down and provide fertilizer for the soil. They also help insulate the soil, keeping in moisture. Homeowners that want to help their own trees should preserve a ring of fallen leaves around the base of the tree, about the size of the canopy.