Northern forests to change as global warming progresses

As a result of global warming, northern forests in the decades to come will look quite different as a new set of trees appear and thrive, while the existing ones find it harder to cope, say researchers from the University of Minnesota.

Their study, which was published in the journal Nature Climate Change (citation below), used a unique long-term outdoor experiment to determine what the effects of climate change might be on the trees in the boreal forest along the Canadian-US border.

Some tree species in the boreal forest are at the far southern edge of their range, while others are at the far northern range of their growing area.

Warmer temperatures have favored trees like maples and oaks, but have not helped species like fir and spruce, which thrive in cooler areas.

Other species, like pine, birch and aspen seemed relatively unaffected.

While all the species may carry on co-existing in a warmer climate, at least for a time, the researchers found that competitively speaking, the balance of power is shifting to the oaks and maples at the expense of the boreal species.

As temperatures rise, fir and spruce may struggle to compete for water and sunlight with neighboring trees, the authors reported.

Heat Lamps and Warming Coils

The B4WarmEd project used heat lamps and warming coils to simulate global warming in plots 10 feet in diameter. (Photo credit: David Hansen, University of Minnesota. Image source: Eurekalert)

Study leader Professor Peter Reich, of the forest resources department at the University of Minnesota, and colleagues simulated the effects of higher temperatures on 10 native and 1 non-native species over three growing seasons at research sites near Ely and Cloquet, Minnesota.

In the project, known informally as “B4WarmED”, the team used infrared heating lamps and soil heating cables to simulate a climate a few degrees warmer on seventy-two plots containing about 4,100 young trees of local Minnesota origin.

They monitored the trees’ growth rates as well as how efficiently they photosynthesized (converted sunlight into energy).

Peter B. Reich

Professor Reich’s current research focuses on the impacts of global environmental change on terrestrial ecosystems. (Image: University of Minnesota)

Although the study did not look at how warmer winters might affect trees and other plant life, the scientists pointed out that winter conditions could intensify the effects observed in this study.

Global warming may speed up the northward invasion of non-native species like buckthorn, the results also indicated. Buckthorn has become more common in northern Minnesota over the last few decades, perhaps slowed by cool summers. However, it did well in warmer experimental conditions.

This is bad news, the authors say, because it suggest that buckthorn and other invasive species could take advantage of warmer temperatures and move up north more aggressively.

Prof. Reich says:

“In the best case scenario, oaks and maples will become more dominant as boreal species decline, and we will have a different, but still functional forest. In the worst-case scenario, oaks and maples will not replace the declining species fast enough, and our forests will be patchy and perhaps filled with invading buckthorn.”

“The change in the forest will influence everything from the supply of timber to habitat for wildlife to its allure for recreational use and tourism. Will people flock to the northern lake country if the woods are full of buckthorn and scattered oaks and maples?”

Citation: Geographic range predicts photosynthetic and growth response to warming in co-occurring tree species,” Peter B. Reich, Kerrie M. Sendall, Karen Rice, Roy L. Rich, Artur Stefanski, Sarah E. Hobbie & Rebecca A. Montgomery. Nature Climate Change (2015.) doi:10.1038/nclimate2497. Received 09 July, 2014. Accepted 11 December, 2014. Published online 19 January, 2015.