Climate change threatens Minnesota's forests | Star Tribune
Today, Minnesota's climate supports forests and trees
Map for current biomes
CURRENT BIOME ZONES
408 parts per million CO2
Even at today's CO2 levels, a variety of ecosystems can thrive in Minnesota, from pine forests to fields.
Forest-
compatible
biomes
In 50 years, climate change could turn most of it to prairie
Map for 2070 biome projection
ONE 2070 PROJECTION
667 parts per million CO2
Current emission rates paired with warmer temperatures could deplete state forests.
Prairie
biome

Climate change threatens our forests

Minnesota's landscape could radically change in coming decades

For years, Minnesota climate and forest scientists have suspected that the state’s tree cover would creep northward as Earth’s climate warmed, and the prairies that predominate in the southwest of the state would take over what was previously a mix of fields, deciduous woods and pine forests.

It wouldn’t happen overnight, but the shift is already underway — prompting concern that Minnesota’s signature forests might be lost altogether.

The technical tools to predict these decadeslong changes with any specificity were always tantalizingly out of reach.

Until now.

CURRENT BIOME ZONES

Current Biomes

ZONE KEY

 
Prairie
 
Prairie forest mix
 
Broadleaf forest
 
Forest mix
 
Boreal forest

Scientists developed worldwide climate projection computer models that were then adapted to predict local changes to Minnesota’s climate and landscape.

Those findings were presented at a series of hearings at the Legislature, with key testimony by Lee Frelich, director of the University of Minnesota’s Center for Forest Ecology and his associates. The core of their presentation was a set of maps of Minnesota and the Great Lakes region showing the current forest and prairie zones and how they will change and migrate to the northeast as the climate warms and precipitation changes.

According to Frelich, a key component of climate change is the increased amount of carbon dioxide and other greenhouse gases in the atmosphere and the way they retain more and more heat near Earth’s surface. Humans have introduced vast amounts of CO2 into the atmosphere over the last 150 years, mainly through the burning of fossil fuels.

Because trees can be sensitive to average temperatures and rainfall, and because Minnesota contains the edges of several biomes where tree species are especially susceptible to change, Minnesota’s forest cover could change rapidly in coming decades. Oaks that are common in western and southwestern Minnesota are likely to migrate north, while the pines of the boreal forest in northeastern Minnesota are likely to recede north and perhaps disappear from the state entirely.

The result of their latest research is nine maps — three CO2 scenarios, each with three different temperature predictions — reflecting thousands of variables that have been painstakingly entered into the computer models.

Ryan Toot, a graduate student in the U’s Natural Resources Science and Management program, said the researchers ran multiple climate models and multiple emission scenarios because “the future is uncertain,” even with most sophisticated forecasting tools. From roughly 40 computer models available to scientists today, U researchers chose three, known as BCC, CCSM4 and Miroc (shown as Warm, Warmer and Hot in graphic below). They capture the range of uncertainty for each of the concentrations of greenhouse gases by choosing cool, average and moderate potential for the region.

Toot wrote the software that calculated the predicted vegetation. The maps have a surprising level of detail, with each square representing a square kilometer.

According to Frelich, “We knew from [research], that the forest and grassland transition occurs right where the climatic water balance is zero — evaporation and precipitation are equal. Where the balance is negative [more evaporation from soil and plants than precipitation], grasslands occur, and where the balance is positive [precipitation greater then evaporation] forests occur.”

Boreal forests, which feature conifers, wetlands and deep clear lakes, occur where mean summer temperatures fall below a certain threshold, Frelich said. Temperate forests occur where the mean is above that threshold.

“With this information, it was possible to analyze the amount of evaporation and precipitation, and mean summer temperature now and in 2070, for each square kilometer,” Frelich said. “If summers are projected to be cool enough with positive water balance, then a given grid square would be boreal forest. Where summers are warm with positive water balance, we have temperate forest. And where there is negative water balance, we have prairie, regardless of temperature.”

Summer climates will, in effect, shift south-southwest by 100 to 300 miles, depending on the scenario, Frelich said. “So Voyageurs National Park could [become] St. Cloud or northwestern Iowa.”

The climate is likely to change too fast for plant species to migrate to their new locations, Toot said. “We’ll probably need to use assisted migration,” which would mean moving and replacing the plants and trees that can’t survive the new climate.

The project is part of an exhibit at the U’s Bell Museum in St. Paul, Weather to Climate: Our Changing World, which runs Feb. 2 to April 28.

EXPLORE THE DATA

Choose a rate of carbon change for the year 2070. Then select one of the models (warm, warmer and hot) and explore the big map below to see how changes would affect your part of the region.

CHOOSE A SCENARIO CHOOSE A MODEL
Global average for CO2 in the atmosphere.
Warm Warmer Hot
1
No change in current rate of CO2 emissions.
667 ppm 515 ppm 436 ppm Neutral BCC667 model CSS667 model Miroc667 model
2
Minor decrease in rate of CO2 emissions.
BBC515 model CCS515 model Miroc515 model
3
Major decrease in rate of CO2 emissions.
BBC436model CSS436 model Miroc436 model
 
Prairie
 
Prairie forest mix
 
Broadleaf forest
 
Forest mix
 
Boreal forest

Credits

Sources

University of Minnesota Center for Forest Ecology, Ryan Toot, Lee Frelich, Peter Reich and Ethan Butler; National Park Service; Beijing Climate Center; Community Climate System Model; Model for Interdisciplinary Research on Climate; Mauna Loa Observatory; IPCC AR5

More info

science2017.globalchange.gov