Birds reflect changing northern forest landscape

"I've seen a red-bellied woodpecker in Ely," said Lee Frelich. "I never expected that."

Frelich is director of the University of Minnesota Center for Forest Ecology, and a fellow in the Institute on the Environment. He and I were visiting on the telephone recently about the impact of changing forest landscape on birds.

He was surprised to see the woodpecker because Ely is out of that bird's normal geographic range.

Why is the bird there? The landscape in that part of northern Minnesota has changed enough to welcome the southern Minnesota species.

The bird mix in northern Minnesota is changing. It's moving from basically boreal to include hardwood-forest birds, like that woodpecker.

"There's been an increase in average annual temperature in the Boundary Waters area," Frelich said. "That is essentially freeing temperate-zone species like red oak and red maple to move into our boreal forest."

Hardwood-forest bird species follow the change.

Oak and maple have invaded the southern 50 to 100 miles of boreal forest in the Boundary Waters area, Frelich told me. That is less noticeable in the eastern, cooler portions of that land.

In a warmer and longer summer, oak and maple grow faster than balsam fir and spruce species, he said. The oak and maple produce more seeds, fir and spruce fewer. The hardwoods out-compete the evergreens.

Before European settlement, the landscape was shaped by frequent wildfire, Frelich explained. It was a patchy mix of old and new growth, of species and age classes.

That landscape provided our present wide variety of bird species.

When logging came, the red and white pines were taken. The pines were replaced by aspen and birch, species that he said are not going to do well in a warming climate.

On drives to Grand Marais for many recent years I have wondered about the stands of dead birch that line sections of Hwy. 61. I thought perhaps they were victims of ice storms.

Actually, Frelich told me, the trees died because of warming soil, droughts during 2000-2010 and invasive earthworms. The worms eat the duff layer, exposing bare ground. Birch roots are sensitive to temperature and moisture. The trees died.

Asked about conifers, Frelich said a warming climate will wipe them out. The natural succession pattern eventually leads to grassland.

This transformation is being helped by insects.

Tamarack trees in northern Minnesota are being killed by a beetle once limited by colder winters. Possibly coming here in the future are mountain pine beetles, insects that have killed millions of pines in the western U.S. They, too, benefit from mild winters.

"They would move east through Canada," Frelich said, and then into Minnesota. "Those beetles can kill all three of our pine species."

"We have dead trees from waterlogged soil, from windblow, from insects," he said. "Eventually, the dead trees will be fuel for fires.

"Unless we mitigate climate change, there will be no recovery," he said.

"In the last 20 years the frequency of all types of disturbances has increased tremendously," according to Frelich.

Woodland warblers, nesting by the millions in our boreal forests and those of Canada, will move north, as will many other species.

Although, since warming is more evident as you move north, just where those birds eventually will find home could be a question.

That red-bellied woodpecker, though, will be very comfortable in the new northern forest.

The question is, will we be comfortable with the new northern forest, the one replacing the Boundary Waters landscape?

Lifelong birder Jim Williams can be reached at woodduck38@gmail.com. Join his conversation about birds at startribune.com/wingnut.