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Study shows deer population reducing valuable North Shore trees

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Mark White, forest ecologist
Mark White, forest ecologist at the Nature Conservancy, talks about the different layers of canopies inside an enclosure protecting a swath of forest from deer and other animals Thursday morning north of Two Harbors, Minn.
Derek Montgomery for MPR

On a blustery day along the shore of Lake Superior, north of Two Harbors, forest ecologist Mark White strides through an old growth forest.

Giant white pines soar 150 feet, and stands of mature cedar trees dot the forest floor. But it's not nearly as healthy a view closer to the forest floor. White notices a tiny white pine sapling that's been munched by hungry deer.

"This guy's been nipped off on the top there a couple times," said White, who works for the nonprofit Nature Conservancy. "Once they've been hit a few times they're probably not going to reach real tree height."

The white-tailed deer is one of Minnesota's most iconic and abundant wild creatures. They lure thousands of hunters into the woods every fall and are adored by children and wildlife lovers. But the deer are taking a toll on our forests. A new study released today documents the drastic impacts deer are having on the forest along the North Shore.

Nearly 20 years ago the conservancy fenced off three half-acre blocks of forest along the North Shore to keep deer out. It left three adjacent blocks untouched, where deer are free to browse. Since then, White has worked to document the differences between the two areas.

On a recent trip there, he stepped into one of the fenced in areas, fighting his way through a dense thicket of plants and trees. 

"If you go through here we're starting to develop a more complex structure in the forest," he said. "We've got a variety of size and height classes here that we don't really have outside."

Protected from deer, the forest is also more diverse and a lot more productive. White's calculations published in the journal Forest Ecology and Management show twice as much biomass in the fenced-in areas. Outside, the forest is much more open under the canopy of huge old trees high above. There are no young cedar or white pines. Deer have eaten them all.

"A lot of these big pines, they're dying, they're getting blown down, and the cedars too, and we're not really replacing those," White said. "There aren't really trees in the subcanopy that can take their place."

To protect the forest, White recommends planting more white pine and white cedar trees — and reducing the deer density.

In 2006, the state Department of Natural Resources did approve far lower deer population goals for northeastern Minnesota, ones that allow hunters to kill up to five deer, including does and fawns.

Mark Johnson, executive director of the Minnesota Deer Hunters Association, said that's aggressive enough. 

"We already are doing some fairly drastic deer population controls, and I really don't think we should go above and beyond that," he said.

Johnson said the DNR should focus instead on planting white pines and cedar.

But the challenge is to keep those tasty saplings away from deer. The animals need woody vegetation to survive the winter, said Bill Schnell, a regional forester for the DNR in Grand Rapids.

"Deer browsing can eliminate a plantation in fairly short order if particular deer develop a taste for our planting stock out there," he said.

Schnell said the state workers plant about a quarter-million white pines every year, mostly in the Arrowhead region. Foresters can build fences around some of them, spray repellants on their needles, or cap their buds to prevent deer from eating them.

But that's expensive and labor intensive on a large scale. With white cedar, though, Schnell said the DNR has given up.   

"Because it's like cotton candy for deer, and they'll go to any lengths it seems like to get it," he said.

Land managers like Schnell have a tough balancing act. On one side foresters say fewer deer means healthier trees. But hunters groups and wildlife watchers want more. When it comes to the deer population, it's hard to pick a number that makes everyone happy.