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On Wisconsin’s oak savannas, there’s some relief from climate-change impacts

An illustration shows painterly views of oak leaves and savannas, divided into vertical strips.
Illustration by Jeremy Nealis.

Trees in the white oak family are expected to thrive and could create oases for species in southern Wisconsin.

This is the third of a four-part series from Sam Harrington tracing a year in the life of Dane County’s oak savanna restoration projects through the seasons. All photos by Sam Harrington.

Elizabeth Macasaet started walking regularly in the Wingra Oak Savanna a year ago. The savanna is part of the University of Wisconsin Arboretum, but it’s also cared for by neighbors from the Dudgeon-Monroe neighborhood where Macasaet lives.

On a summer day, Macasaet often passes birdwatchers, friends catching up over cups of coffee, and older couples going for a walk. She’s also seen kids playing in the trees.

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“One group of kids looked like they were up to a bit of mischief up there, which is always good to see,” she says.

The neighborhood has been deeply involved since savanna restoration began in the early 1990s. When the Arboretum started clearing brush and trees to free the 200-year-old oaks, neighbors were initially upset. But when Arboretum staff brought neighbors into the process and educated them about the unique and important ecosystems of savannas, the neighborhood joined in on the work.

Decades later, a summer walk through the Wingra Oak Savanna features dappled light over blackcap raspberries and wildflowers. Bikers may pass by on their way to work or just out for a ride. Less than a block off busy Monroe Street, the dominant sounds come from birds and insects. 

“It’s so accessible and yet feels private and quiet,” Macasaet says. “Kind of that forest bathing feel that you look for when you go into nature.”

The savanna also helps keep the neighborhood cool and provides a shady place for people to get outside on hot summer days. I met Macasaet at a coffee shop near the savanna on a hot Friday afternoon. Stepping under the oak canopy after walking along Monroe Street felt like entering another world. 

Parks and greenspaces with trees help counter urban heat islands, in which pavement and the built environment hold heat and raise temperatures. This is particularly important as climate change makes cities even hotter.

Daytime temperatures haven’t risen much yet in southern Wisconsin’s summer months, but they are expected to increase four degrees Fahrenheit by 2050. It’s also projected that Wisconsin will have three times as many days above 90 degrees Fahrenheit by 2050 as compared to the end of the 20th century. Summer nighttime temperatures have already begun to increase and are up two degrees Fahrenheit in 2020 as compared to 1950.

Steve Vavrus, the co-director and senior scientist at the Wisconsin Initiative On Climate Change Impacts, thinks that our wetter summer climate is influencing temperature trends. 

“When it’s wet, that tends to depress the daytime temperatures,” he says. “We get more clouds. We get more rain. We get more haze. All of those things depress how hot it gets during the daytime. But all of those things can also trap heat at night and keep the temperatures from falling as much.”

Summers in south-central Wisconsin are already 20 percent wetter than they were in the 1950s. Climate models disagree about whether that trend will continue in the future. Some suggest Wisconsin’s summers will get drier and others that it will get wetter. Either way, extreme rainfall events are projected to become more frequent and severe.

These kinds of heavy rain events flush runoff into Madison’s lakes, which creates poor water quality. After a series of storms in early July, Madison and Dane County closed beaches on Lake Monona due to the presence of E. coli. The Wingra Oak Savanna helps slow runoff and filter pollution before it pours into Lake Wingra. Urban savannas like Wingra can help manage stormwater and urban heat as our climate changes. 

Thanks to the types of oak trees present in Wisconsin’s savannas, these landscapes are expected to be up to the challenge.

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Lily-pads, flowers and algae grow on dark water around large branches floating and protruding from the water
The Wingra Oak Savanna is just up the hill from Lake Wingra.

Some iconic Wisconsin trees, particularly those common in northern forests, are expected to struggle with warm temperatures that cause stress and make them more vulnerable to pests and disease. Red oaks are vulnerable to a fungus-caused disease called oak wilt. White oaks, on the other hand, have demonstrated some tolerance to the disease and are expected to manage climate change well.

The most common oaks found in Wisconsin’s oak savannas are bur oaks and white oaks, which both are members of the white oak family. 

“Oaks in general, they survive and thrive in really different environments,” Brian Miner, the Nature Conservancy’s Southeast Wisconsin Land Steward, says. “We have oaks on sand barrens. And then on the other end of the spectrum, there are oaks that are growing right in, basically, the edges of wetlands.”

Understory species in oak savannas are also well-adapted to temperature and moisture variations. Miner says that the stability of savannas will likely provide critical habitat for plants and animals as they attempt to adapt to climate change.

“It provides a lot of those micro-habitats that are important for how species move across the landscape, and, ultimately we think, for how they will move and adapt to climate change in terms of migration,” he says.

This is good news not only for wildflowers, pollinators and migratory birds, but also for people. 

The ecosystem services—like heat and stormwater management—of oak savannas will become even more vital as the climate changes. And oak savannas can actually help mitigate climate change itself. Trees and grassland ecosystems are important carbon sinks.

“Not only are oak trees very good at storing carbon, but the prairie flora, the real diverse understory species, [are] actually sinking carbon into the soil,” Miner said. “Having healthy oak savannas across large areas, in combination with other ecosystems, can definitely help mitigate climate change.”

As we move through this period of intense change, we do so alongside savanna oaks. Perhaps it’s time to take a cue from the kids in Macasaet’s neighborhood and spend a day playing in the trees.

Large oak trees are silhouetted by the sun setting behind a prairie

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