If you want to plant a pine tree that might survive the climate upheavals that are already remaking northern Minnesota’s boreal forest, where should it go?
Scientists from the Nature Conservancy and elsewhere now think they know. This summer they’re embarking on a project to plant 400 acres with cold-loving evergreens like jack pine and tamarack in carefully selected “conifer strongholds” — places that they predict will stay cooler or wetter or have better soil, increasing the chances that a few of each species will survive for the next generation as Minnesota grows warmer.
“We are trying to get us in better shape for the centuries to come,” said Meredith Cornett, a forest scientist with the Nature Conservancy in Minnesota who is heading up the project.
The aim is to preserve northern forest species — not just the trees but also the mosaic of plants and animals that rely on them — to maintain biodiversity.
Both will be exceedingly difficult thanks to a double whammy of the region’s past and its future.
Conifers like white and jack pine, white cedar, and tamarack once made up two-thirds of Minnesota’s northern forest. But thanks to logging, development and the deer that followed both, they’ve declined to about half, and aspen have become just as common as conifers.
Now, climate change is forcing a different kind of evolution on the southern, most vulnerable, edge of the boreal forest. The giant, long-living pines are disappearing, replaced by more southern species like red maple as tree species across the country move in response to rapid changes in temperature and moisture brought on by 100 years of rising carbon levels in the atmosphere.
A study of 86 eastern tree species published last week by Purdue University scientists found that many have already migrated west in response to increased rainfall in the central part of the country, and north in response to higher average temperatures.
Climate scientists predict that, even if global carbon emissions are held to the rates agreed upon in the Paris Climate Accord, average temperatures will rise by 2 to 4 degrees Fahrenheit by the end of this century. That means the pines of northern Minnesota would give way to a hardwood and grass ecosystem, said Lee Frelich, a University of Minnesota professor who studies climate change and forests.
If that’s what happens, then the conifer stronghold will work, he said. But if carbon emissions and climate change continue to accelerate, then in time, northern Minnesota will instead look a lot like Kansas, Frelich said, and no boreal species will survive long-term.
Cornett hopes to provide conifers more time on the Minnesota landscape no matter what happens.
She and foresters from the University of Minnesota and elsewhere have identified 30 such strongholds, totaling 400 acres, in the forests north of Duluth and in the St. Louis River watershed, where they will plant seedlings this year. Next year they plan to plant 50,000 more at other sites in northeast Minnesota.
Cornett and her fellow researchers are relying on a hugely dense set of historic data that includes temperature, humidity, elevation, proximity to water and land use to identify spots in today’s forest that can become strongholds for the cold-loving trees. That would include, for example, the north side of a slope or a low-lying wetland area.
Those spots already exist in other parts of Minnesota, Frelich said. For example, there’s a low-lying tamarack bog in the western suburbs of Minneapolis that exists because, for some reason, colder air is funneled there. And in southwest Minnesota, a stand of balsam fir is an island in a sea of grass and row crops because it sits on a steep north-facing slope inundated with unusually cold groundwater, he said.
The conifer stronghold data comes from a much bigger effort by the Nature Conservancy to map and identify areas across the national landscape that are most likely to promote biodiversity in the future. In short, rather than tracking and protecting places because of the species that are there, it focuses on geology. A limestone valley, for example, will be home to a different set of species than a granite mountain no matter what the climate.
“Species are important, but they are going to change over time,” said Mark Anderson, the Boston Nature Conservancy scientist who is heading the project nationally. “We want to conserve these stages so they have a place to thrive.”
The East Coast mapping is complete, and the Great Lakes region — which includes Minnesota — is underway. Anderson said the difference between the two is striking. In the east, for example, changes in elevation and topography can create micro climates and ecosystems. In the flatter Midwest, water, wetlands and river systems drive biodiversity, he said. But the immense expanses of agricultural land form a kind of barrier to tree migration, making it far more difficult for species to evolve and move with the climate.
“It’s powerful,” he said. “It gives us a way to think about conservation in a changing world.”