Even Modest Warming Could Cause Major Changes in Great Lakes, Canadian Forests

Even relatively modest climate change could dramatically alter Minnesota's Northwoods and the southern boreal forest that runs from eastern Canada to Alaska, according to new research recently published in Nature.

These changes could have devastating implications for one of the planet's largest intact forests, which provides timber, houses biodiversity and helps slow climate change by holding on to a significant portion of the planet's terrestrial carbon.

A team of researchers led by Peter Reich, a professor in the Department of Forest Resources at the University of Minnesota, conducted a rare long-term experiment to find out how climate change would impact seedlings and saplings of nine tree species common in the southern boreal forests.

Over the course of five years, the researchers used infrared lamps and soil heating cables to study the projected impacts of near-term climate change. In the experiment, more than 4,500 seedlings and saplings on two forest sites were warmed around the clock, from early spring to late fall. The sites were at University of Minnesota field stations in forests near Cloquet and Ely, both in northern Minnesota.

The researchers conducted the experiment using two different levels of potential 21st century warming. They tested 1.6 C (2.9 F) and 3.1 C (5.6 F) above ambient temperatures, which varied from hour to hour and day to day. They also studied precipitation shifts under a changing climate by using movable tarps to periodically capture rainwater on some plots before it reached the plants and soils. A control group of trees was grown at ambient temperatures and moisture levels.

"Our results spell problems for the health and diversity of future forests," said Reich.

The scientists found:

• Warming alone, or combined with reduced rainfall, increased mortality of all nine tree species and severely reduced growth in several northern conifers that are common in boreal forests, including balsam fir, white spruce and white pine.
• In contrast, modest warming enhanced growth in several broadleaved hardwoods that are scarce in the boreal forest but much more common in temperate forests further south, including oaks and maples.
• Oaks and maples are unlikely to rapidly fill the void left by vanishing conifers.

"Present-day southern boreal forest may reach a tipping point with even modest climate warming, resulting in a major shift in the kinds of species present, and with potential adverse impacts on the health and diversity of our forests," said Reich. "Those impacts could reduce the capacity of our forests to produce timber, host other plant, microbial and animal diversity, dampen flooding and perhaps most important of all, scrub carbon out of the air and hold it in wood and soil."

The forests of the northern reaches of the Great Lakes states and the much vaster forests of much of southern Canada are at risk of failing to regenerate well, leaving a future forest with uncertain capacities to provide for nature and for people.

Continued research is needed to better understand such changes through combinations of experiments, observations and models. Unfortunately, this type of long-term experiment is rare. This study and one related study in a spruce bog in northern Minnesota are among the only such long-term studies in the world.

This research was supported by the U.S. Department of Energy, the National Science Foundation, the Minnesota Agricultural Experiment Station, and the University of Minnesota.