Warmer weather, human disturbances interact to change forests

While a rapidly changing climate may alter the composition of northern Wisconsin’s forests, disturbances such as logging also will play a critical role in how these sylvan ecosystems change over time.

Details will be presented on Friday, Aug. 6, at the annual Ecological Society of America conference in Portland, Ore.

University of Wisconsin-Madison researchers used a computer-modeling program to project 200 years of change in a forest in northwestern Wisconsin under three climate scenarios. In one scenario, they assumed no change from current temperature and precipitation conditions; in the other two scenarios, they used data from global forecasts that predict a hotter, wetter climate.

The model also took into account land development, along with processes like harvesting and changes in carbon storage due to climate change.

“If the climate were to warm, we project that many northern species would not be able to reproduce or compete well, and southern species that are adapted to warmer conditions, such as the oaks and hickories found in southern Wisconsin, would move in,” says Robert Scheller, a UW-Madison postdoctoral forestry researcher with the College of Agricultural and Life Sciences.

In fact, Scheller and forestry professor David Mladenoff found that some species – including jack pine, red pine, white spruce, balsam fir and paper birch – would not be able to survive warmer conditions.

But human actions also contribute to this changing landscape, according to the results.

Says Scheller, “Human influence greatly modifies change in the forests, and logging and fragmentation would affect the northward migration of southern species during a period of climate warming.”

Although scientists know that species migration occurs as the climate changes – there is evidence of this from the last ice age, Scheller says – for at least the next 100 years, disturbances such as harvesting or wind damage will continue to play a very important role in shaping forests.

“Harvesting helped create the forests we know today, and will continue to be a primary driver of change,” he says. “If the climate changes, harvesting may provide opportunities for southern species to take hold in northern forests.”

However, there is a natural lag between climate change and species migration, says Scheller, adding that this lag is especially evident in environments that are fragmented by human development, such as parts of northern Wisconsin.

The project was completed using a newly released forestry-modeling program called LANDIS II, which is an expansion of the previous LANDIS program. Forestry scientists at UW-Madison and the U.S. Forest Service North Central Research Station developed both programs.

Scheller and Mladenoff are now applying their new model to areas outside of Wisconsin. They are teaming with NASA to model insect defoliation using satellite images, and are working with the U.S. Forest Service to examine the effects of fire in the pine barrens of New Jersey.