New Forest for a New Climate

“Head forward,” Drew Rindflesch calls out to a crew of Conservation Corps of Minnesota and Iowa workers. “Just look for the baby trees.”
Leaves are down; breeze whips off Lake Superior. The crew’s neat line inches along, bending and then falling apart as workers repeatedly stoop over white pine and northern white cedar seedlings to prune away overhanging raspberry canes and rip out encroaching native bluejoint grass so the seedlings get more sunlight.

By day’s end, the workers treat nearly 20 acres in Split Rock Lighthouse State Park, one of four North Shore state parks where the DNR is working with The Nature Conservancy on a project to replant hundreds of acres of forest.

Something makes this project different from what might have been done 20 years ago. Rather than draw from local seed sources to replant the forest of the recent past, resource managers are using a diverse mix of seedlings, some drawn from more than 100 miles to the south. The goal is a subtly different, more resilient forest that will thrive in a warmer climate.

“We’re keeping a component of the trees everyone wants on the North Shore—the cedar, the spruce, the white pine,” says Liza McCarthy, DNR district resource specialist who works for state parks. “But we are adding in species that we wouldn’t normally plant in large numbers in the past.” These “climate winners” include red oak and yellow birch. “They’re expected to do well, they belong here, but it’s new to plant them in large numbers,” she says.

The state parks reforestation is one among many forestry projects around the country to adapt forests to a changing climate. The approach upends the old paradigm of preserving the forest as it existed before European settlers. In some cases, foresters, ecologists, and other land managers are actively moving in new species from as far as hundreds of miles away to prepare forests for a warmer climate.

The change is an adjustment for resource managers—such as those at state parks—who have sought to preserve a sample of the past, and a challenge for those who have to figure out what might thrive in the future.
“We are kind of paving a new path,” 

McCarthy says. “So it’s a little challenging because we are trying new things. It’s supported by data and science but it is still different than what we’ve done in the past.”

Problems for today’s North Shore forests began a century ago when loggers clear-cut the big pines and logging-slash fires burned the remaining woods down to mineral soil. In areas like Split Rock Lighthouse State Park, paper birch took hold, spreading in pervasive even-aged stands.

Those birch stands, now age 90 and counting, are dying. The result is obvious in a drive along the North Shore northeast from Two Harbors, where misshapen birch snags perch on hills like vultures. Underneath grows a thicket of hazel, raspberry, and native grass. With the combination of underbrush, a lack of regular low-intensity fires, and browsing whitetails, which are far more common than they were a century ago, tree seedlings don’t stand much chance. Says McCarthy, “We’re not seeing natural tree regeneration that you would in a generally healthy area of forest.”

Worse, forest pests such as white pine blister rust, spruce budworm, and bronze birch borer have been imported or are spreading due to a warming climate. Most dramatic is climate itself. Warmer winters, drier summers, and more intense rainstorms are causing iconic species such as white spruce, eastern white cedar, and paper birch to struggle. In another century, the mismatch between climate and tree species will be much worse.

Forest managers, foreseeing a brushy grassland on much of the North Shore, recommended a major reforestation effort when Split Rock Lighthouse State Park rewrote its resource plan in 2018, says park manager Katie Foshay. Opportunity knocked when a private foundation made an anonymous grant to The Nature Conservancy to demonstrate forest management projects that help adapt forests to climate change while also sequestering carbon in the roots and trunks to reduce, however slightly, the amount of the greenhouse gas carbon dioxide in the atmosphere. The North Shore parks were one of three projects that each “had at the core this idea of carbon sequestration and adaptation together,” says Meredith Cornett, climate change director for The Nature Conservancy in Minnesota, North Dakota, and South Dakota. “It was very much designed for the resilience of the Great Lakes ecosystem.”

In all, 100,000 seedlings have been planted in the past year at Split Rock Lighthouse, Gooseberry Falls, Temperance River, and Cascade River state parks. The seedlings are a mix of white pine, red oak, bur oak, yellow birch, white cedar, white spruce, and tamarack. The oaks are clear climate winners. White pine and yellow birch are local species that are expected to do well in a changing climate. White spruce and tamarack were planted because they don’t require protection from deer. Iconic boreal trees such as spruce, cedar, and birch were planted on north-facing slopes and similar shady “microclimates” with cooler soil temperatures. 

“We are still planting trees that aren’t projected to do well with climate change, but we’re considering where they are planted,” says McCarthy. “People love them and they’re great animal habitat and part of our plant communities here.”

The new trees seem to be thriving so far, but it will take years to know if the strategy was successful. Says McCarthy, “I’ve been happy with how the trees look so far.”

These North Shore sites aren’t the only parks forced to adapt their forests to a changing climate. Nerstrand Big Woods State Park in southeastern Minnesota has lost many of its namesake towering sugar maple, basswood, oak, hickory, and other hardwoods. A wetter climate and heavier rains in recent decades have killed trees on poorly drained soil. (See “When a Tree Falls in the Woods,” May–June 2020.)
“We’ve got 150-plus acres of really nice mature Big Woods forest that died off and is not going to come back,” says Ed Quinn, DNR Parks and Trails natural resource program supervisor. 

As on the North Shore, at Nerstrand, park managers are drawing on species they wouldn’t have planted a generation ago, such as silver maple and Dutch elm disease–resistant elm. They are native to the general area, but not to Nerstrand specifically. Says Quinn, “We’re trying to reestablish a native community, but not the one that was there before.”  

The idea of transitioning to a new forest, of introducing species or genotypes that were never or rarely found on a site, of taking seeds from distant sources can be unsettling to some of the people who manage parks, scientific and natural areas, and other sites that operate under a goal of preserving a slice of the pre-settlement landscape. 

Says Quinn, “So many of us who have been in this field for decades—our touchstone was always pre-European settlement conditions. Those were the reference sites. That’s what you looked at and said, OK, that’s what we’re trying to restore.”

“What should our new goals for restoration ecology be, in light of the fact that replicating historical conditions is no longer going to be possible?” asks Cornett of The Nature Conservancy. “I would describe that as a real crisis of confidence in some ways for ecological restoration and restoration ecologists, because we’ve often used these historical references to guide our work.” 

Interest in climate adaptation might be even keener among county, state, federal, and tribal foresters with “a multiple-use mindset” than among park managers, says Stephen Handler, climate change specialist for the Forest Service Northern Research Station and Northern Institute of Applied Climate Science. For managers of working forest land, manipulating a forest for specific objectives is everyday work. “In many cases it’s a lightbulb moment when people realize some of the practices we already consider as smart forest management are perfectly in line with climate change adaptation,” he says.

That’s important because these folks manage forests for wood products, wildlife, and recreation on some 15 million acres in Minnesota (about 60 times the acreage of Minnesota’s state parks). Amanda Kueper, applied science coordinator for DNR Forestry, feels the weight of managing Minnesota’s 4.2 million acres of state-administered forest land. “We have a big responsibility to make sure that those forests are going to be able to persist on the landscape well into the future,” says Kueper. “So we definitely are thinking a lot about climate adaptation.” 

Foresters have a range of strategies for dealing with climate change. The most conservative is “resistance”—as Kueper explains, “looking for places like climate strongholds and places where we don’t expect there to be as drastic a change because maybe it’s a protected microclimate.” Some of the planting on the North Shore is a good example. In Chippewa National Forest, foresters are thinning red pine stands to leave remaining trees with more soil moisture.

A bit more aggressive is “resilience,” says Kueper. “Resilience is really about promoting forest health and recovery from disturbances. And to do that, we might have to tweak the forest ecosystem as it is, and that might look like increasing the diversity of tree species that are present at the site and making sure that we’re incorporating more species that are going to be climate winners, that are more resilient against the future climate.”

Again, the North Shore parks provide a good example. Another is found in Minnesota’s black ash swamps, threatened indirectly by climate change as warmer winters have allowed the emerald ash borer to spread in the state. Says Kueper, “Our big concern in forestry is that eventually this insect is going to find its way to north-central Minnesota where we have a million acres of black ash swamp across our state forest lands and kind of wreak destruction and havoc there.”

State foresters have employed a resilience strategy in an ash swamp near Warroad in northwestern Minnesota. They recently planted a mix of not-quite-native-to-the-site red maple, silver maple, bur oak, swamp white oak, and black spruce so that when most of the ash die, the site persists as a forest.

The most far-reaching and controversial method of forest adaptation is “assisted migration.” Species may be moved hundreds of miles, completely out of their native range, to new areas where they are expected to flourish in a warmer climate. Assisted migration has been avoided by Minnesota state foresters and the crews working on the North Shore parks partly out of caution and also because DNR policy was only recently changed to allow forest managers to plant more southerly genotypes and species. Says McCarthy, “You have a little more flexibility now, but we still want to do it carefully. And you want to monitor your results and not apply it broadly until you know how it will turn out.”

In some cases, assisted migration aims to save endangered plant species that are isolated and threatened with extinction as climate becomes unsuitable in their native range. A good example is the endangered yew Torreya taxifolia, known as “the rarest conifer in North America.” It survived only in tiny areas of Florida and Georgia until the volunteer Torreya Guardians transplanted specimens to sites throughout the Appalachians and Midwest, as far north as southwestern Wisconsin.

Assisted migration can also involve moving common species to new locations—not to protect individual species but to diversify a forest and help it thrive under changing conditions.

Among the research leaders is the Cutfoot Experimental Forest in the Chippewa National Forest in north-central Minnesota. “This is the largest assisted migration experiment in Minnesota for sure, likely in the [Great] Lakes states and beyond,” says Brian Palik, research scientist for the U.S. Forest Service. 

The 3,000-acre experimental forest is dominated by red pine stands that grew in the wake of fire a century ago. Researchers have been looking at silvicultural practices such as thinning, and mixing in different species in the understory to determine what might succeed in a warmer climate. “Novel species” from more southerly reaches, such as white oak, bitternut hickory, and black cherry “are going like gangbusters,” says Palik. Seedling survival after six years is nearly 100 percent.

One of the wildest experiments has been finding a potential replacement for the red pine itself. It is Minnesota’s state tree, and red pine stands, such as those at Itasca State Park, are beloved. Nonetheless, the species is vulnerable to drought and, according to some models, will shrink away to the northeast.

“The worst-case scenario is that red pine doesn’t do well in the future,” says Palik. “We thought, what’s a potential alternative that is similar ecologically, economically, and culturally? Ponderosa pine may be it.”

Yes, Ponderosa pine. In Minnesota. The closest native population is in the Black Hills. “That,” says Palik, “is truly assisted species migration.”

Ponderosa pine looks nearly identical to red pine. (In fact, Scottish botanist David Douglas originally misidentified it as red pine.) Ponderosa pine is suited to warmer, wetter winters and hotter, drier summers, both predicted in northern Minnesota. “They grow better than anything else that we planted,” says Palik.

Tribal and industry foresters in particular have been interested in bringing in species from surrounding areas, says Palik. The Leech Lake Band of Ojibwe has expressed interest in more oak because acorns are valued as a traditional food, he says. And the timber industry places high value on Ponderosa pine and black cherry in their native ranges.

Whether Ponderosa pine ever finds a significant foothold in Minnesota is up in the air. What is not in question is that Minnesota’s forests will be changing, either as a result of die-off and regeneration, or because forest managers anticipate and facilitate a new assemblage of species. 

Either way, there’s no standing still. As Palik says, “The climate of southern Minnesota has been in northern Minnesota for at least 20 years.”