气候变化领域集成服务门户

Assisted tree migration in Michigan

TRAVERSE CITY, MI – Luke Kreykes plunged a metal garden spade into the wet soil along the Boardman River shoreline where it loudly scraped against underground stones that used to be part of the river bottom.

It didn’t make for easy digging, he said, but the parkland steward for nonprofit Grand Traverse Conservation District didn’t need the hole to be very big. He stooped to plant a swamp white oak seedling that appeared little more than a twig.

This wasn’t a typical springtime tree planting project.

The scientific idea behind growing that lowland tree species as far north as Traverse City when its traditional range reaches only into southern Michigan is to build resilience to climate change within the forests. The question remains whether swamp white oaks and other more southerly tree species can be artificially migrated north to help fight the effects of climate change and eventually fill gaps in the forests caused by losses to woodland diseases and invasive insects.

“A lot of this is just climate change awareness. It’s a pretty proactive land management approach,” said Reb Ratliff, the parkland steward who led a two-day tree-planting event just outside Traverse City on April 21 and 22 for Earth Day.

In fact, answers about how well certain trees can transition into more northern zones are coming from multiple places across Michigan. That includes efforts by conservation groups, tribal governments, and community science projects all focused on protecting the state’s signature forests.

Mitch Lettow thinks quite a bit about the effects of climate change on Michigan’s forests as the stewardship director for the nonprofit Southwest Michigan Land Conservancy.

He researched how ecological tension zones – northern and southern boundaries of adaptation by plants and animals – can be expected to shift as climate change increases temperatures and alters weather patterns. Those shifts may be key to understanding climate adaptations.

Lettow’s project is to test new northern reaches of suitable habitat for more southerly tree species. It’s especially important as those species lose habitat along southern range boundaries as the climate also changes at lower latitudes, he said.

Tree species naturally migrate on their own, but it takes centuries and generations of evolution. Lettow argued that given the generational timeline of trees, they are unlikely to keep up with the current rate of climate change.

That’s when the ecologist asked himself, “what if trees had feet?” Would they keep pace with climate change if they moved north?

Lettow said some trees are not expected to be resilient to climate changes in Southwest Michigan, such as American beech, Eastern hemlock, yellow birch, and even white pine – the state tree. That eventually will leave holes in Michigan’s forests – lost biodiversity.

Tree species he’s now testing out as possible ecological replacements through an “assisted range expansion” study include sycamore, pawpaw, blackgum, tulip poplars, Kentucky coffee tree, honey locust, and red mulberry. Experts believe those species may do well further north because of climate change.

Lettow suggested the best way to try out more southerly tree and shrub species are as part of restoration efforts at previously disturbed lands, such as old cropland, heavily logged tracts, or abandoned tree farms. For example, his reforestation test plot involves 6,000 trees and shrubs planted at an old Christmas tree farm at the Wau Ke Na Preserve North Tract near Fennville.

Similar habitat restoration work and tree range testing are goals at the Traverse City tree planting site near the Boardman River.

The riverside area where dozens of volunteers planted trees was formerly beneath the old Boardman Pond, an impoundment behind the now-removed Boardman Dam. A decade-long effort to remove three dams on the river exposed lands conservation officials are now trying to reforest.

Parkland Steward Luke Kreykes of the Grand Traverse Conservation District dumps a bucket of wood chips around the base of a large swamp white oak he planted with the help of volunteer Jim Kure (left) of Traverse City. Other volunteers in the background are planting much smaller tree seedlings.

Ratliff said two species they are testing out in the Boardman River Valley are swamp white oak and tulip poplar trees. Those are added to the landscape along with more than a dozen native species already known to thrive locally, such as red maple, black cherry, gray dogwood, and common paper birch.

They hope to learn whether the more southerly species will grow well among other native trees and be resistant to both rising temperatures and the threats of disease and invasive pests, which have already decimated trees like elm and ash.

“A diverse forest is going to be a more resilient forest, considering different invasive pests and pathogens that keep showing up,” said Ellie Johnson, regional forester for Benzie, Grand Traverse, and Leelanau counties.

She manages an up-north community science project to assist tree range expansion across Benzie, Grand Traverse, and Leelanau counties. Participants buy seedlings of the species in the study through their conservation district tree sales and are asked to monitor the vitality, height growth, foliage quality, and bark conditions of their planted trees over time.

Johnson said she hopes conservationists from other parts of Michigan want to replicate the tree range science project and find the best species to help migrate into their specific regions.

One major reforestation project that embraced assisted tree migration is at the Leelanau Conservancy’s Chippewa Run Natural Area in Empire, not far from the Lake Michigan coast.

The preserve was an old apple orchard left untended and at risk for invasive species, which could put nearby active farmland in danger of also being affected by problematic pests. The conservancy partnered with Conservation Resource Alliance and the Grand Traverse Band of Ottawa and Chippewa to remove both the old apple trees and some invasive black locusts growing there.

Contractors have been on site in recent weeks to re-plant much of the preserve after plantings in 2021 failed because of an extremely dry summer that year. All the tree seedlings going in the ground there this year are native to Michigan.

Tree planting contractor Gideon Koster of Wayland tamps down the earth around a white pine seedling planted at Chippewa Run Natural Area in Empire as part of a restoration of an old apple orchard.

However, bur oaks planted among the mix are part of the range expansion experiment. The historical northern boundary for that species tops out in southern Michigan.

“We’re trying not to put our thumb too heavy on the scale,” said Caleb Garone, land steward for the nonprofit conservancy.

Tribal experts said they are hoping to help restore forestland to a region that was once rich with old growth trees and a diverse ecosystem left heavily altered by the post-settlement lumber era of the 1800s.

“This whole area up here used to be forested,” said Melissa Witkowski, tribal fish, wildlife, and soil conservationist for the Grand Traverse Band.

She said restoring former farmland like the old orchard to more natural conditions will help maintain native habitats and build resiliency to climate change. She also said it’s part of protecting and preserving the land for the next seven generations of the tribe, a key Anishinaabeg principle.

The Anishinaabeg peoples of the Great Lakes are comprised of Indigenous tribes across the United States and Canada, including the Ojibwe, Odawa, and Potawatomi of Michigan.

“By planting native species, we’re hoping to prevent invasive species from moving in and taking over and then hurting the biodiversity that wants to be here and should be here,” Witkowski said while standing in the heart of the up-north preserve.

Melissa Witkowski is the fish, wildlife, and soil conservationist for the Grand Traverse Band of Ottawa and Chippewa Indians. She said restoration work planting trees at an old apple orchard in Empire includes a variety of species, including bur oak, which is expected to have an expanding range because of climate change.

Scientists with the Little Traverse Bay Bands of Odawa also have experimented to learn which more southerly tree species could grow on tribal lands. They planted at an old farm site and in gaps in the existing forest canopy.

Conservation Biologist Derek Hartline said his predecessor at the Harbor Springs-based tribe began planting in 2016 and used many of the same species of trees being tested in the Traverse City area: tulip poplars, shagbark hickory, swamp white oak, and sassafras, among others.

He said though he wasn’t involved when the tribe planted 18 acres for the project, he now does annual evaluations on how the assisted range expansion trees are faring. He said the tribe may restart those planting efforts should the trees show a high success rate and limited mortality in five or 10 years.

“We’re preparing for climate change shifts where it will be warmer here in the next seven generations,” Hartline said. “We’re not going to be able to see how this forest does in 100 years, but the next generations will.”