On a blustery spring day, Jed Meunier MS’05 and his team are climbing Wisconsin’s Castle Rock bluff, searching for treasure. From the outside, the gnarled pine stumps look dull. But cut them open with a chainsaw, and they can reveal centuries of the state’s fire history.

“It’s like cracking open a geode,” Meunier says. “You can’t really predict what’s inside.”

Instead of looking for sparkly minerals when he takes them back to his dendrochronology lab at the Wisconsin Department of Natural Resources (DNR), Meunier seeks out the dark rings that tell the story of centuries past, including fire scars, formed when the trees attempt to heal their burns.

Fire ecologists know that these sandstone cliffs in the state’s southwestern Driftless area are a good place to find the oldest pine relicts because they were too steep and rocky to be cleared for farming. Today, his search crew includes DNR scientist Bob Smail, UW–Platteville geography professor Evan Larson, and James Riser, a former DNR employee who works as a freelance researcher. Riser spots a likely “snag,” a standing dead tree, on the next cliff, and the team sets off to cut a sample from it.

In 2014, Meunier found a stump in the nearby Snow Bottom valley that was a sapling in the 1600s. It now bears the scars of some of Wisconsin’s big wildfire years — 1754, 1805, 1891, 1895, and 1910. The later years are corroborated by newspapers and settlers’ accounts. But before the settlement era, the trees themselves are the main historical record of the blazes that swept the land.

In northern Wisconsin, Meunier has found fire scars that link Wisconsin to one of the country’s first reported massive fire events, known as “New England’s Dark Day.” On May 19, 1780, the skies of New England grew so dark that candles were lit at noon, and the preachers prophesied the end of the world. The cause was actually massive fires around the Great Lakes, where thousands of acres of forest were ablaze. Ash would follow, dropping like sooty snow across New England.

Meunier’s research has also rewritten our understanding of what happened Oct. 8, 1871, when the Peshtigo fire roared up both sides of the Bay of Green Bay, killing as many as 2,500 people in the deadliest fire in American history. Generations of Wisconsin schoolchildren learned that the lumberjacks were to blame because they left behind piles of flammable pine slash. But it turns out the loggers were just scapegoats. The true story is more complicated.

Using land surveyors’ records of “witness trees” and tree ring analysis from 659 fire-scarred trees from 25 sites in Wisconsin and Michigan, Meunier built a history of fire in the north from 1548 to 1947. In a study published earlier this year in the journal Fire Ecology, Meunier concluded that the trees that fueled the Peshtigo inferno were the same hemlock, cedar, beech, tamarack, and sugar maple that grow in that region today. The great cutting of the pinery had not yet begun.

What fueled the Peshtigo fire were two dry years that spawned numerous smaller fires. That year it was so smoky on Green Bay that a lighthouse was kept lit during daytime hours to guide ships. Then, in October, cyclonic winds swept in from the Great Plains, whipping those small fires into a maelstrom.

“What we learn from Peshtigo is that it was climate and weather driven . . . and we need to be prepared for that to happen again,” Meunier says.

While the Fire Ecology study prompted a reinterpretation of the past, another study published last year in Forest Ecology and Management may change U.S. Forest Service (USFS) practice going forward. A team of researchers (including Meunier, Eric Rebitzke of USFS, professor Volker Radeloff PhD’98 of the Department of Forestry and Wildlife Ecology, and Colleen Sutheimer MS’21, a recent forestry master’s student that Radeloff and Meunier co-advised) looked at fire history in the peatlands of the northern forest.

Peatlands have been a “carbon sink” since the last Ice Age, sequestering as much as 25% of Earth’s soil carbon and thus keeping the planet cooler. Rebitzke, a fire manager for the USFS, said he contacted Meunier after seeing research about historical fire regimes in Missouri and asked him to work together on studying the peatlands of the Hiawatha National Forest. It’s part of a larger effort that includes the Sault Ste. Marie Tribe of Chippewa Indians. Tribal members interviewed elders, who told of burning peatlands to encourage the growth of medicinal plants and berries.

“Peatlands are just magnificent carbon sinks,” Meunier says. “They make up less than 3% of the world’s surface, but they sequester more carbon than all the trees on earth combined, tucking it away in these unique, low-oxygen environments.”

They studied fire history via tree rings from islands within three peatland complexes in the Northwoods, finding that between 1548 and 1955 low to moderate intensity fires burned through these wet areas every seven to 34 years.

“To our surprise, we found that low severity fires were quite frequent prior to the middle of the 20th century,” Meunier says. Fire suppression ended those historical fires. But just as Western states now face catastrophic fire seasons because of all the built-up fuel, Meunier says that halting peatland fires could be a mistake.

“Peatlands are really well engineered by nature,” Meunier says. “A low-intensity fire burns only the top of the peat, and it regenerates. What happens when we suppress fire is that we risk changing the system from low-severity fires to high severity. The worst thing imaginable is a fire that burns down into the mineral soil and releases 10,000 years of carbon.”

Because of Meunier’s research, Rebitzke says, the USFS is going to include peatlands within the Ottawa and Hiawatha national forests in its prescribed burns. A new joint research project in the western Upper Peninsula is also being planned.

“He’s filling in major gaps in our knowledge about the historical role of fire in the upper Great Lakes,” says Rebitzke of Meunier. “We’re using that data to inform our prescribed fire implementation strategies.”

Some of Meunier’s current research is using dendrochronology to understand the role of fire in encouraging the regeneration of red pine, an iconic Wisconsin species that is threatened by climate change.

Before earning a doctoral degree from Colorado State University, Meunier received a master’s degree from the CALS Department of Forestry and Wildlife Ecology, which was founded by his great-grandfather, Aldo Leopold, in 1939. Meunier is the DNR’s first “disturbance ecologist,” which means he studies how factors such as wind, fire, and harvest have shaped Wisconsin’s landscape.

“People know about his changing views on predators,” Meunier says of Leopold’s famous essay about seeing the “green fire” die in the eyes of a wolf he shot in New Mexico. But few know Leopold also went through a similar evolution in his thinking about fire.

Meunier notes that his great-grandfather began his career in the Southwest in 1909, a year prior to some of the most destructive wildfires ever recorded in the northern Rockies. In 1923, Leopold wrote an article calling fire “a scourge of all living things,” although he noted that he had to give the “fire devil” its due because it did encourage beneficial species. By the mid-1940s, Leopold and his UW students were setting fires to restore prairies at the UW Arboretum.

“When he was a young USFS employee, he thought that fire was the evil of all evils,” Meunier says. “But he came to see it as a powerful tool.”

Meunier is the fourth generation of the Leopold family to study how fire shaped the American landscape. His great-aunt Estella Leopold is a well-known paleobotanist emerita at the University of Washington, and great-uncle Starker Leopold BS’36 wrote the 1963 Leopold Report that advised the National Park Service to restore natural processes such as fire. That recommendation was highly controversial, as was Starker’s call for California to use fire to manage quail.

Meunier’s grandmother, Nina Leopold Bradley, and her husband, Charles C. Bradley, returned to the famed Leopold shack on the Wisconsin River to start and direct the Aldo Leopold Foundation. Meunier grew up nearby in Baraboo. Later, at UW, he studied woodcock s for his graduate work, using methods he later learned were developed by his great-grandfather.

“I came across a photo of Aldo weighing and sexing a woodcock in front of the Shack,” Meunier says. “Until then, I didn’t realize the methods we are still using were developed by him.”