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David Goldblum
NIU Professor David Goldblum counts the seedling density of a plot of sugar maples in the Blackberry Maples Forest Preserve near Elburn.

Lesley Rigg
NIU Professor Lesley Rigg examines sugar maples seedlings under a microscope.

Shannon McCarragher
Graduate student Shannon McCarragher monitors sugar maple seeds germinating in a growth chamber at NIU.

To obtain a print-quality JPEG of this photo, contact the Office of Public Affairs at (815) 753-1681 or e-mail

News Release

Contact: Tom Parisi, NIU Office of Public Affairs
(815) 753-3635

September 25, 2007

NIU scientists, students will bring
global warming to Canadian sugar maples

DeKalb, Ill. — For about 2,000 sugar maple seedlings now growing in Canada’s Lake Superior Provincial Park, global warming will arrive next spring.

Northern Illinois University geographers Lesley Rigg and David Goldblum have been awarded a $260,000 grant from the National Science Foundation to simulate global warming on sugar maple seeds and seedlings and study the effects over three years.

Rigg and Goldblum, working with NIU students, will travel in May to Canada, where they will build rain-exclusion, temperature-controlled structures over existing seedlings in a forested area of Lake Superior Provincial Park.

The structures will allow the researchers to simulate temperature increases and dryer conditions predicted to occur over the next century.

The sugar maple is the dominant tree species in the northeast portion of the United States and a keystone species of forests in eastern North America. Prized for its hardwood and known for the maple syrup made from its sap, the sugar maple is considered to be of great ecological and economic importance.

Sugar maples can reach 400 years of age and 120 feet in height. They thrive in cool, moist climates, with seeds germinating at about 1 degree Celsius (34 degrees Fahrenheit).

“Mature trees may be able to handle warming temperatures, but scientists need to determine whether the trees will be able to successfully reproduce and whether the species will be able to migrate northward to cooler climates,” says Rigg, who holds a joint appointment at NIU in geography and biological sciences.

Scientists expect global warming to be most pronounced in higher latitudes. Environmental mitigation will require early identification of potential problems.

“When it comes to climate change, there tends to be a focus on the direct impacts on humans, such as sea-level change, killer heat waves or negative impacts on agriculture,” Goldblum says. “But one of the more vulnerable aspects of global warming is the balance of our ecosystem. Scientists are concerned that animals and plant species won’t be able to respond to rapid change.”

The Canadian Regional Climate Model (CRCM) predicts monthly temperature increases of 4.2 degrees Celsius (7.6 degrees Fahrenheit) for the study area over the next 75 years. Some researchers have suggested that sugar maple trees, which now extend south all the way to Georgia, could disappear completely from the United States.

“Under some climate-projection models, you can write off the sugar maple in its southern limits, even though warming there won’t be as pronounced,” Goldblum says. “In order to survive, the species has to be able to move north.”

Located on the eastern shore of the world’s largest freshwater lake, Lake Superior Provincial Park marks an ideal setting to study the sugar maple’s ability to migrate. The site of the experiment is within a transition area from deciduous forest to boreal forest, the latter dominated by coniferous trees.

“We expect that our experimental design of simulating a range of temperature and moisture regimes will capture conditions that the sugar maple will experience in the northern part of its range sometime in the next 100 years,” Rigg says.

Adapting to gradual climate change, the sugar maple has slowly migrated northward over time. But projections of human-induced climate change suggest that warming over the next several hundred years will be faster than anything the sugar maple has experienced within the last 18,000 years, or possibly within the past 2 million years.

“If predictions are correct, the changing climate will force the sugar maple to move faster than it has ever moved in its history—and through a fragmented landscape of streets, parking lots and subdivisions,” Rigg says.

NIU researchers and students recently returned from Canada, where they tagged the seedlings that will be studied, dividing them into about 20 plots, each measuring about 1 by 2 meters.

Meanwhile, work also is being done on campus at NIU.

Graduate student Shannon McCarragher is monitoring sugar maples that have been germinated in growth chambers and treated to different temperatures. The seedlings come from seeds collected in Tennessee, Illinois and Michigan’s Upper Peninsula.

“It may be that seeds and seedlings from the south, where temperatures have been warmer for thousands of years, will more readily survive in the north under conditions of global warming,” Goldblum says.

The study is expected to be completed in 2010.