A University of Minnesota study published earlier this week reaffirmed that the thick stands of majestic evergreens defining northern Minnesota's forests are slowly giving way to a patchy mix of oaks and maples. And invasive buckthorn, already a menace in the southern part of the state, is primed to fill in the gaps.
"It's already happening," said U of M forest resources professor Peter Reich, who led the series of experiments dubbed "B4WarmEd." "More oaks and maples are showing up when surveying younger trees than what you would've seen 30 or 40 years ago."
Reich's team of researchers just concluded the long, ambitious outdoor experiments testing how different tree species respond to slightly warmer ambient temperatures. They used infrared heat lamps and underground cables to maintain a simulated growing environment that was 3 to 6 degrees Fahrenheit warmer than whatever temperature it was outside.
Average temperatures in Minnesota have already gone up more than a degree during the last 50 years, and due to accelerated climate change are projected to rise 2 to 3 more degrees over the next 50 years, according to Reich.
The study found oak and maple trees thrived under the warmer conditions, spruce and fir struggled, and aspen, birch, and pine trees were neutral.
Reich said the results of this small-scale study corroborate what Canadian foresters are already seeing in large-scale tree surveys in southern Canada. The coniferous giants are retreating into the arctic, and oaks and maples are following in their wake.
Buckthorn's spread will probably make the new forests even uglier. The invasive, shabby bushes are a big problem in southern Minnesota, but haven't taken to northern Minnesota by the same degree.
"Our data suggest we can't rely on the cold to slow [buckthorn] down. It's already here, and it's probably going to become more and more abundant," said Reich.
"The worst-case scenario is that spruce and fir don't do well and buckthorn really does well. Then we'll have a patchy forest with a lot of buckthorn in it in about 40 or 50 years," he added.
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