Last Saturday was too hot and muggy for a 30-mile bike ride. But since I was never the smartest kid in class, there I sat, dismounted, panting and sweating on a bench in Mears Park, thankful for a cold soda from the drink cart and all those tall, shady trees.
This is my favorite urban park in the Twin Cities, an island of green loveliness surrounded by some of St. Paul’s most beautiful historic buildings. Yet on a day so sweltering, not even this spot could keep my mind from drifting toward cooler climes. I imagined the piney shores of Lake Superior and the sparkling lakes of the Boundary Waters before recalling Lee Frelich and his disturbing discovery about what’s happening to Minnesota’s north woods. It kind of took the edge off my daydream.
Remember the big blowdown of 1999? Starting on the afternoon of July 4, a massive derecho packing violent winds of more than 90 mph swept along the U.S.-Canada border for 1,300 miles. In all, the storm lasted 22 hours. It blew down nearly a half million acres of trees in the Superior National Forest, including about 40 percent of the trees in the Boundary Waters Canoe Area Wilderness.
For Frelich, director of the University of Minnesota’s Center for Hardwood Ecology, the blowdown and its aftermath of fires and forest regeneration confirmed on a massive scale what he had long suspected: The new north woods growing up to replace the millions of blown down trees isn’t really a north woods at all but something more akin to the grassland savannahs farther south. Indeed, over the last decade or so, the blowdown has become a giant laboratory for measuring the ecological effects of a warming climate and the role humans are playing in accelerating the change.
Prairie replaces forest
Most of the trees lost in the storm were pines and aspens, Frelich told me this week. By normal succession, they would be replaced initially by varieties of spruce, fir and cedar. But instead red maple, basswood and other species normally found farther south are sprouting on the forest floor. “Recently I was at Snowbank Lake near Ely and I was just amazed to see all the red maple coming up,” he recounted.
Frelich admits that until the last few years his observations greatly depressed him. He loves the woods, after all. He grew up in the grip of Sigurd Olson’s lyrical writings about the magic of the northern wilderness. To realize that Minnesota’s thick, dark canopy of conifers would be replaced by, in Frelich’s words, “a scrubby, species-poor landscape” was not a pleasant prospect. But he’s no longer angry. He tries to see the blowdown in a broader perspective — as part of the paleo-ecological record and as an opportunity to gather more data to chronicle the changes ahead. He holds out little hope than humans will alter their carbon habits enough to prevent the intrusion of prairie into the forest.
A journal article to be published next month in Frontiers of Ecology and Environment further documents Frelich’s findings. He and his U colleague Peter B. Reich, professor of forest ecology and tree physiology, explore likely changes over the next 50-100 years in the composition of northern forests due to global warming.
“Under a scenario of human-induced global warming, the prairie biome will shift to the northeast and displace existing forests,” the paper declares. Here’s a summary of its observations:
Think of Minnesota as having an ecological border running across it diagonally, northwest to southeast. To the northeast, boreal forests dominate the landscape. To the southwest, savannahs — prairies with small trees that do not close to form a canopy — prevail. Over the last million years, the border has shifted eight times, but this time is different; the conifer forests are retreating to northeast farther and faster than before because there are higher levels of carbon in the atmosphere (twice the pre-industrial concentration).
A perfect storm of events
Likely accompaniments to this ecological trend? A warmer, drier climate that outstrips the ability of tree normal species to keep pace with the change; a greater rate of evaporation; more severe wind storms; a greater number of severe fires that give warmer-climate plants a better opportunity to invade; more exotic insects and diseases affecting trees; an overabundance of deer that browse woody plants that would otherwise grow into trees; and the further invasion of earthworms that disturb the forest floor’s ability to hold moisture. (As it turns out, nightcrawlers and angleworms, imported to use as fishing bait, are not native to Minnesota.)
“All of those factors are pushing the forest in the same [northeast] direction,” Frelich told me. “My best guess is that the BWCA Wilderness will look more like a savannah than a boreal forest within five to 10 decades.”
Altogether, he and Reich report in their writings an expectation that the lost of forest along the prairie-forest border of central North America could equal an area twice the size of California.
“There’s no doubt that human activity has made this a unique, super-charged event,” Frelich said.
Inpact on the urban landscape
Frelich describes what might be called an ecological reset. Higher levels of CO2 in the atmosphere have set off a chain of events. Plant life adjusts to changing conditions. Forest becomes prairie. Habitats change. Animals adjust.
Maybe it runs parallel to the reset taking place in the world of human settlement. Jim Erkel, land use and transportation director for the Minnesota Center for Environmental Advocacy, offers the analogy. Conditions for humans are changing. Not only do we have a warming climate and an unstable energy supply, we have a faltering economy and significant demographic shifts toward smaller households.
What’s required is a reset, Erkel suggests, citing the Austrian economist Joseph Schumpeter’s theory of “creative destruction.”
Economic crises sweep away outmoded companies, practices and systems, clearing the way for entrepreneurs to introduce new technologies and new ways of doing things that reignite growth.
In that context, we can’t build cities the same old way, Erkel said. Conditions require a spatial fix, a new development pattern that’s more that’s more compact and energy efficient. Some people will resist these changes, complaining about loss of basic freedoms, the rising price of gasoline or the falling values of large suburban homes, for example. But maybe, said Erkel, moral values aren’t really involved. Maybe changes in the urban form should be viewed as similar to the ecological adjustments being made in Minnesota’s northern forests.
“There is no right or wrong in the way nature resets itself to changing conditions,” he said. “It’s just the way it happens.”
Related: Two articles by Frelich and Reich
• Wilderness Conservation in an Era of Global Warming and Invasive Species: A Case Study from Minnesota’s Boundary Waters Canoe Area Wilderness (2009)
• Will environmental Changes Reinforce the Impact of Global Warming on the Prairie-Forest Border of Central North America?