MINNESOTA — Almost everywhere he looks, Lee Frelich sees the fingerprints of climate change on the forests he has studied since he was a boy half a century ago.
Birds from southern Minnesota are now popping up far north in Ely, on the edge of the famous Boundary Waters Canoe Area Wilderness. Splashes of red maple leaves are now visible each fall amid the pines and spruces of the iconic North Woods, where they once would have been harder to find.
Frelich, the director of the University of Minnesota's Center for Forest Ecology, thinks that if the state's warming trend remains unchecked, such subtle changes will become starker and more devastating in the decades ahead. He thinks the boreal forests that soak up huge amounts of carbon dioxide from the atmosphere could disappear entirely, taking with them a third of the state's native species of trees, flowers, birds and pollinators.
In an extreme scenario, he has warned, prairie land could expand across much of Minnesota by 2100, the timber industry, tourism and the state's very identity.
"Minnesota could become the new Kansas," he said. "We have a perfectly good Kansas now. We don't need a second one in Minnesota."
Frelich is among a small army of scientists working to understand the subtle but unmistakable shifts that are unfolding in one of the nation's fastest-warming states — shifts that he and others say will become more profound and troubling in the hotter future that lies ahead.
They are running ambitious experiments that simulate rising temperatures with heat lamps and underground wires, use computer models to decipher where certain species might thrive and involve planting trees from as far away as South Dakota that might one day take the place of native species stressed by heat.
A Washington Post analysis of historical temperature data found that seven counties in Minnesota have warmed more than 2 degrees Celsius (3.6 Fahrenheit) since the late 19th century — about twice the global average. Winters here have warmed even faster, with 59 of the state's 87 counties — about two thirds — eclipsing the 2C threshold during the months of December, January and February.
Minnesota is home to a landscape like none other in the United States. It has the boreal forests to the north, with their stately conifers and the moose and lynx that roam them; temperate forests in the middle, dominated by deciduous trees such as oak and maple; and vast prairie stretching to the south and west.
But rising temperatures are altering those boundaries.
Experts in the state have testified about what is in store if temperatures continue to rise: more heat-related deaths, lower crop yields, damaging deluges and floods, a surge in pests, increasing drought and worsening air quality.
Scientists differ on whether Frelich's most extreme predictions for Minnesota's forests are too pessimistic. But there is little doubt that unsettling changes are underway.
"The forest can't perpetuate itself the way it once did," said Chris Swanston, a U.S. Forest Service ecologist and director of the Northern Institute of Applied Climate Science. Forests are always evolving, he added. "It's just with climate change, things are changing faster and in different ways. We're having to roll with that change a lot faster and be a much more active part of it."
That fast change contributes to some "zombie" forests in parts of the state, said his colleague Stephen Handler, a Forest Service climate change specialist.
"There are places where climate change is already influencing forest regeneration," Handler said. "Big, healthy trees overhead — but on the forest floor, no baby trees to fill in the gap."
The fate of Minnesota's forests depends in large part on humans and whether they can significantly reduce carbon dioxide emissions that fuel warming trends, Frelich told state lawmakers last year, adding, "There's still time to change the outcome."
But in the meantime, researchers continue to look for creative ways to help the state's forests adapt and endure.
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SQUAW LAKE, Minn. — The storm clouds had lifted, and the late-afternoon sunlight filtered through the towering red and white pines that dominate this corner of the Chippewa National Forest.
"When people think of the North Woods, they think of this type of forest," said Brian Palik, a longtime ecologist with the Forest Service's Northern Research Station.
He was standing in the middle of one of the largest climate adaptation experiments of its kind in the world, which also happens to reside in one of the country's fastest-warming spots. Itasca County, near the headwaters of the Mississippi River, has warmed 2.1 degrees Celsius (3.8 Fahrenheit) since the late 19th century, according to data analyzed by The Washington Post.
Palik moved gingerly through the understory, stopping every so often at young trees that traditionally have no place in these woods. But in recent years, the U.S. government has backed a project to transplant about a dozen non-native species here, as researchers try to answer an increasingly urgent question: Can humans help trees keep pace with climate change?
Palik pointed out bitternut hickory from southern Minnesota and Illinois. Black cherry and white oak, whose historical range has been 100 miles or more to the south. Ponderosa pine from Nebraska and South Dakota.
What is becoming clearer is that the non-native trees from warmer, drier climates are largely thriving here.
"They are doing really well," Palik said. "My argument is, the climate for them is here now."
The experiment, which began in Minnesota nearly six years ago, is one of six sites around the country where the federal government and academics are testing a range of approaches aimed at helping forests — and the ecosystems that depend on them — adapt to a rapidly changing climate.
Across hundreds of acres, the Forest Service has planted about 275,000 seedlings as part of the massive experiment that Palik oversees.
The project involves several approaches. Some plots are left virtually untouched. In other areas, workers have thinned trees and managed the forest to shield the native pines from heat stress and drought.
But the boldest part of the experiment is known as "assisted migration" — planting of trees that once would not have been found here, but that are expected to flourish in the future that scientists foresee in Minnesota's North Woods.
Palik knows that the approach is controversial and that it could be expensive to deploy on a wide scale. But he says the forests that Minnesotans cherish — the ones that support the timber industry, recreation, tourism and wildlife — face serious risks in the decades ahead unless humans intervene.
"The worst-case scenario is if we don't do something like this, we'll have no forest," he said. "Our broad objective is to look at ways to keep forests on the landscape. It may be a different forest. I like to say that it may not be your grandfather's forest, but it will be your grandchildren's forest."
Even as the changes to the state's iconic forests are still unnoticed to many, Palik feels an urgency to lay the groundwork to keep the woods as productive and alluring as they are now.
The climate is changing "at a rate that's unprecedented in geologic history," he said. "And plants, including trees, don't migrate at that same rate." There are also obstacles — roads, parking lots, agricultural fields — that make the trees' slow migration north more difficult.
"So we're helping things move," he said.
As darkness set in, Palik headed out of the serene national forest, away from the trees he hopes hold important answers for future generations, and back toward Grand Rapids along State Highway 46.
"It's not that this is going to happen. It's that it's already happening," he said of the changes that the warming climate is bringing to the North Woods.
"The time to act is now."
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CLOQUET, Minn. — Along a small dirt road not far off Interstate 35, hidden behind a tall chain-link fence, sit dozens of small, circular plots ringed by humming heat lamps. At first glance, the scene looks more like an illicit growing operation than a cutting-edge climate experiment.
But these peculiar patches of earth serve a unique purpose: to offer scientists a glimpse of what climate change might mean for Minnesota's forests.
"We are heating simultaneously above and below ground," Artur Stefanski explained one afternoon as he wove his way through the maze of heat lamps, temperature gauges and underground wires that he has helped manage for years as a research fellow for the University of Minnesota.
Each test plot, about 10 feet in diameter, includes nearly a dozen species of trees — spruces and paper birch from the boreal forests that stretch to the north, as well as more temperate red maple and oaks, whose range extends largely to the south.
Here in Cloquet, perched on the edge of two critical biomes, researchers are constantly heating the air and soil of certain plots nearly 2 degrees Celsius (3.6 Fahrenheit) and more than 3C (5.4F) above ambient temperatures. The goal is to glean answers about how forests will fare in the hotter decades that lie ahead for Minnesota, parts of which already have experienced significant warming.
The project, which has been underway for more than a decade, has a mouthful of a name — Boreal Forest Warming at an Ecotone in Danger, or B4WARMED for short — but a clear objective.
"We're trying to create, in an ecologically realistic way, the climate of the future," said Peter Reich, a professor and forestry expert at the University of Minnesota who helped conceive of the experiment. "It's like a time machine we're trying to create, so that we know what is going to happen."
Reich argues that the most important strategy is for the nation and world to find ways to slash carbon emissions and slow climate change, because "we're cooked if we just try to adapt our way out of this." At the same time, knowing what perils lie ahead for Minnesota's forests is key to figuring out how to help them — and forests like them — adapt before it's too late.
"If the existing forests die and you don't get fast enough recovery from other species, then you get a lot of problems," Reich said, such as reduced water quality, more wildfires and air pollution, a devastated timber industry, and the loss of wildlife. But "if you've helped it to adapt, you can help keep biodiversity."
Year after year, both in Cloquet and at another test site several hours' drive north in Ely, a steady stream of university researchers have kept the time machine running. Every 10 seconds, a computer takes temperature readings and adjusts the heat to keep the plots at just the right level.
Researchers have taken thousands of measurements about the trees' growth, their photosynthesis, when their leaves emerge in the spring and when their colors change in the fall, and how they fare over time.
"We're testing who's going to win the race to become the next generation of trees" to dominate the forests of northern Minnesota, Reich said.
Clear pictures have emerged. The more northern, or boreal, species such as spruce and fir have struggled in a 2C or 3C world. Their growth is slower, their mortality higher. The oaks and maples have, for the most part, emerged as climate change winners, along with invasive shrubs such as buckthorn, which can spread rapidly and choke out the biodiversity of a forest.
What does that tell scientists about the future that awaits Minnesota?
At the very least, trees that grow in temperate climates, such as maples and oaks, are likely to become more dominant, altering the face of the boreal forests that have made northern Minnesota unique in the landscape of the Lower 48.
In a darker scenario, Reich said, the oaks and maples won't replace the declining species of trees quickly enough, and once-alluring forests will turn patchy, less productive and far less friendly to wildlife — and tourists.
For now, the time machine whirs on. The heat lamps keep warming. The search for answers continues.
"How could you study forests these days and not study climate change?" Reich said. "It's the elephant in the room."
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TWO HARBORS, Minn. — On a cool, clear day, Meredith Cornett and two colleagues from the Nature Conservancy hiked through an impossibly green forest not far from the banks of Lake Superior.
The air was heavy with the scent of pine and cedar, birch and balsam. Cornett's boots squished along a muddy path as she spoke about loss and shifting expectations.
She once imagined that she would spend her career restoring the majestic conifer forests of northern Minnesota that had been devastated by logging and poor forest management.
"Climate change threw a boomerang in the whole system. I still remember the day I realized unequivocally that we weren't going to be able to bring these species back to where they were historically," said Cornett, the science director for the organization's chapter covering Minnesota and the Dakotas.
As a young scientist, she was determined to help revitalize the diversity and grandeur of those forests — and the wildlife that depends on them. A decade and a half ago, she was among the crews that fanned out across the state to plant millions of conifer seedlings across hundreds of sites. She viewed each as a small "green flag of hope" that might help bring back the most robust version of the North Woods.
"Turns out, we were underestimating the degree to which climate change would disrupt our ambitious plans," she later wrote. Many of the trees that she was eager to help flourish once again were already at the southern edges of their range in Minnesota. And the state's rapid warming is pushing that boundary ever farther north.
"Climate change has stealthily set in motion a hundred little things that together will most certainly render northern forests of the future unrecognizable," Cornett wrote. "For me, that meant embracing the notion that to 'save' the great Northwoods might mean transforming it."
That realization led her to adaptation.
"This is about trying to help the forest itself transform and keep pace with a rapidly warming climate," she said as she walked through the serene woods. "We see ourselves as troops with a mission — to help the forest help itself."
In recent years, Cornett and her colleagues have focused on a simple goal: to keep the "woods" in the North Woods, even if that means something different from generations past. She says a functioning forest — as opposed to the shrub land or grassland that could dominate here if Minnesota's warming continues unabated — is critical to wildlife habitats, carbon storage, the timber industry and water quality.
The group has tried various approaches to ensure that these woods remain intact, including planting new mixes of trees such as red oak and bur oak that are likely to fare better in a hotter, drier future. They also have turned to data, teaming with other researchers to use computer modeling that predicts what changes forests will face 200 years in the future under various scenarios. They have identified cooler-than-average spots on the landscape, such as north-facing slopes and moist areas where conifers might flourish for years.
The work has provided a road map about where and what to plant.
"We had to come to grips with the fact that things are going to change pretty quickly, and then decide, what can we do?" said Mark White, a Nature Conservancy forest ecologist.
Their answer is to plant trees, hundreds of thousands of them, where the science shows they might fare the best. Oaks on warmer sites, conifers in cooler spots.
Green flags of hope.
"These are actions we can take right now that we think will make a difference," White said.
On this day, they had come to check on several of the hundreds of test plots around Minnesota, to measure how seedlings are holding up against insects and disease and hungry deer, not to mention climate change.
Afterward, they hiked up a steep trail to a clearing high above the forest floor. In the distance, sunlight gleamed off the vast expanse of Lake Superior. Below lay the ever-changing forest, blanketed in aspens and cedars, red pines and the occasional sugar maple.
"That is what we are hoping to preserve," said Ryan Sullivan, a field ecologist.
"At least some of it," White said.
Cornett stared quietly into the distance.
"There's still a long way to go," she said.
This article was written by Brady Dennis, a reporter for The Washington Post.