Scientists in northern Minnesota are exploring how to adapt forests for climate change, transitioning them to a warmer future by planting new mixes of southern seedlings. In this “transition test” in the Cutfoot Experimental Forest, forest ecologists thinned trees and planted seedlings of eight species, grown from seeds collected up to hundreds of miles to the south. CREDIT: BRIAN PALIK / USDA FOREST SERVICE

Thanks to John Tibbets and Knowable Magazine

This 8-year-old bitternut hickory, native to a milder climate to the south, is flourishing in northern Minnesota, notorious for long, intensely cold winters. CREDIT: BRIAN PALIK / USDA FOREST SERVICE

Moving trees north to save the forests

As the world warms, trees in forests such as those in Minnesota will no longer be adapted to their local climates. That’s where assisted migration comes in.

On a brisk September morning, Brian Palik’s footfalls land quietly on a path in flickering light, beneath a red pine canopy in Minnesota’s iconic Northwoods. A mature red pine, also called Norway pine, is a tall, straight overstory tree that thrives in cold winters and cool summers. It’s the official Minnesota state tree and a valued target of its timber industry.

But red pine’s days of dominance here could fade. In coming decades, climate change will make red pine and other Northwoods trees increasingly vulnerable to destructive combinations of longer, warmer summers and less extremely cold winters, as well as droughts, windstorms, wildfires and insect infestations. Climate change is altering ecological conditions in cold regions faster than trees can adapt or migrate.

Palik, a forest ecologist with the US Department of Agriculture’s Forest Service Northern Research Station, stops and points to a newcomer under the red-pine canopy: a broadleaf deciduous tree, bitternut hickory, as high as an elephant’s eye at about 10 feet tall and eight years old. “It’s doing really well,” he says.

This bitternut hickory probably shouldn’t be thriving in the Cutfoot Experimental Forest in north-central Minnesota, near Grand Rapids. It likely began as a seedling in a nursery in Illinois, to the south, where deep freezes are less extreme. Normally, if a southern-adapted seedling is planted in an unsuitably cold climate like this one, it can risk frost damage and its survival is threatened. But the newcomer’s lush, green foliage exudes good health.

It is a promising sign in a project that aims to keep forests growing in a warming world.

In the Cutfoot Experimental Forest in 2016, the Forest Service planted seedlings of eight tree species from seeds, collected from woods up to several hundred miles farther south, as part of an experiment that Palik manages. Four species are native to this northern region: eastern white pine, northern red oak, bur oak and red maple. Four species are uncommon or nonnative: white oak, bitternut hickory, black cherry and ponderosa pine.

Two decades back, these southern seedlings likely would have struggled to flourish here. Today, Palik and his team can see the success of almost all the southern trees they planted. “They are going like gangbusters,” he says, “which is indicative that the climate is right for them,” although the researchers don’t know about the seedlings’ long-term health yet. In seven of the eight species, the survival rate has been 85 to 90 percent.

“The climate typical of southern Minnesota from 20 years ago is now in northern Minnesota,” Palik says. Climatic conditions have moved about 200 miles north in just two decades.

Palik’s project is an experiment in forest assisted migration, the relocation of trees to help woodlands adapt and flourish despite the heating of their habitats from climate change. Foresters advocating assisted migration are typically not aiming to save specific species — instead, by moving trees, they want to help sustain productive forests for multiple benefits such as carbon storage, water filtration, wildlife habitat, recreational beauty and timber.

Experimenting with assisted migration calls for a different way of thinking about nature. Whereas ecological restoration typically looks to the past for cues on repairing degraded places, foresters exploring assisted migration are planting warmer-climate trees that could have a better chance of thriving under warmer future conditions…

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