Without fire, red pines could disappear, model shows

In the northeastern corner of Minnesota stand towering groves of red pine trees stretching some 80 feet into the sky.

But these red pine groves could eventually vanish from Minnesota’s Boundary Water Canoe Area if what we usually view as a foe to forests — fire — fails to sweep the terrain occasionally, says a new study from the university.

“The big, natural groves of red pine are one of the most unique features of the BWCA. But, because of fire suppression, we’re starting to lose them forever,” says Robert Scheller, a UW–Madison forest ecologist working with professor David Mladenoff.

Before people settled the area in the early 1900s, fires — started primarily by lightning bolts — swept through the area every 50 to 100 years. While the blazes reduced most vegetation to ashes, they enabled the surviving trees, such as the red pine, to reproduce more easily.

“The fires cleared dense brush so the red pines could drop their seeds on the forest floor and also triggered the release of seeds from pine cones belonging to other fire-adaptive trees,” Scheller says.

However, when settlers started taking active measures to suppress natural fires, red pines experienced more difficulty regenerating: other trees and shrubs filled the forest understory. This growth inhibited the red pine from seeding and remaining a key part of this northern ecosystem.

“Red pines have a life span of about 300 years,” says Scheller, “and many of the ones in BWCA are already old.” Without fire to help them successfully reproduce, he adds, it’s unlikely that the older trees will be replaced once they die.

Nearly a century after fire suppression was first introduced, the U.S. Department of Agriculture-Forest Service is now considering the use of fire in the boundary waters area. To explore the long-term effects continued fire suppression and regular burnings, Scheller has developed a model that shows the outcomes of both scenarios. The findings were presented today, Aug. 5, at the annual meeting of the Ecological Society of America.

“We wanted to know the consequences of different kinds of future forest management over the BWCA,” he says. “Would reintroducing fire bring back the red pines?”

Taking into account the species’ ages and life histories, as well as forest composition, climate and soil, Scheller used the landscape simulation model LANDIS, which was developed at UW–Madison, to predict what might happen across the entire area if fire was reintroduced. Specifically, Scheller studied four scenarios over a 300-year time period: continued fire suppression and fires about every 50, 100 or 300 years.

The model shows that continued fire suppression would lead to the disappearance of not just red pines but also jack pine, aspen and birch trees within 300 years. “If full fire suppression continues,” Scheller explains, “the forest may never recover and red pine may be lost as a locally dominant species.”

The model suggests that while a fire every 300 years would preserve red pines, it would not save the jack pine, another tree species dependent on fire for reproduction. Fires every 50 to 100 years, as they once occurred naturally, would maintain tree diversity; and, a fire every 50 years would increase the number of red pines.

Fire suppression policies implemented in this century and advocated by icons like Smokey Bear, are meant to preserve the natural beauty of forests, says Scheller. But as he points out, “the model shows that fire is a necessary process for maintaining the natural community. Without it, the characteristics that define the wilderness of the BWCA will completely change.”

Scheller’s work is funded by the USDA Forest Service, which plans to use the model to develop a long-term perspective on fire and forest management.