Foresters brace for brutal fire season as drought adds to threat to Minnesota's trees

Kindling is piling up on the forest floor. Beetles, pests and diseases that have been attacking Minnesota's core tree species over the past several years have turned entire stands into the ready-made fuel of fallen branches and dead trunks. Now a hot and dry spring, with more abnormally dry weather expected well into summer, has foresters bracing for what could be a brutal wildfire season.

And they're worried about the impact a prolonged drought will have on Minnesota's trees.

More wildfires had already broken out across the state by mid-June than in all of last year. The state typically has fewer than 1,200 wildfires a year, burning roughly 25,000 acres. So far this spring, more than 1,425 fires have burned roughly 35,000 acres of forest and grassland, according to the Department of Natural Resources (DNR).

"I don't see it going anywhere or mitigating soon," said William Glesener, DNR wildfire operations supervisor. "This is a period when we should be having very few fires, but we're adding about 50 a week. We're really going to be in it in a couple weeks when things really dry out."

Wildfires are typically at their worst in the spring and fall, slowing down in the summer when trees and plants are fully green and rain picks up. But a summer reprieve may not happen this year.

More than half of Minnesota is in a drought, with an increasing swath of southeastern Minnesota in severe drought. Long-term forecasts from the National Oceanic and Atmospheric Administration (NOAA) expect the drought to continue through the summer.

The dry spell comes at a precarious time for the state's canopy. Hundreds of thousands of acres of balsam fir trees north of Duluth have either died or are struggling to fight off a bloom of a pest called spruce budworm. About 90% of the state's tamarack trees have been killed off in just the past five years. Oak wilt and the emerald ash borer continue to spread farther across the state, leaving dead oak and ash in their wake.

While a drought alone wouldn't kill mature trees for quite some time, it weakens them to the point where they can't fight off insects, pests and diseases, said Brian Schwingle, central region forest health specialist for the DNR.

"Most native insect pests and pathogens are opportunists," Schwingle said. "They don't cause problems unless trees are stressed."

Trees are starting to show early signs of stress. Oaks, especially young saplings, are starting to lose their leaves. Without rain soon, the branches of some maple trees will likely start showing fall colors by early July, Schwingle said.

The major effects of a drought are often delayed, he said. Two of the state's worst droughts in recent memory were in 1988 and 2012. Massive tree die-offs from those dry spells didn't happen until one, two or even three years after the drought ended.

That's because it takes time for beetles and pests that burrow into drought-weakened trees to finish them off, Schwingle said.

Foresters and loggers are preparing for wildfires as best they can.

The DNR has been targeting tamarack, ash and balsam fir trees on state-owned forests, trying to log them before they die.

St. Louis County has lowered the price of its balsam fir trees to make them more attractive to loggers.

"If the logger doesn't have a market for balsam fir, sometimes we'll have them lay the trees down, so they're flat on the ground and can rot a lot faster than if they were left standing," said Jason Meyer, deputy director of St. Louis County's land and minerals department.

The next month will be telling for how bad the damage will be, said Matt Russell, University of Minnesota extension specialist.

"What concerns me right now is our oaks and pines," Russell said.

While oak and pine are generally hardy and resistant to drought, most of those trees in Minnesota grow in the southern part of the state, where the drought is at its worst and the soil is sandy. The sandy soil doesn't retain water nearly as well as the clay found in much of northern Minnesota, he said.

"If we see another few weeks without rain, I would start to be more concerned about all of our forests," Russell said.

One problem is that the soil is now so dry that short spells of rain don't slow down the state's wildfires for very long, Glesener said.

"When we get as dry as we are, the amount of water we need essentially doubles, because moisture gets pulled so much deeper into the soil," he said.

What the state needs is steady, consistent rainfall, about three quarters of an inch per week, he said.

It's not just the lack of rain that's a threat, but also the heat.

The reason so many of Minnesota's tamaracks have died is because earlier springs and later winters have allowed a native bark beetle to produce an extra generation of young before winter, University of Minnesota researchers found. While the trees can handle the damage caused by one generation of the beetle, the second generation proves fatal.

After a historically hot June, the beetles may already be off to a strong start, Russell said.

"In a really warm year you'd expect more generations of the beetle to emerge," he said.

To help any beloved trees in yards survive the drought and fight off pests, the best thing to do may be to water them, said Rachael Dube, forest health specialist for the DNR.

The DNR recommends placing a hose at a trickle, under the tree's drip line — the point where rain would naturally drip off the leaves — for about an hour on all four sides of the tree once every two weeks until steady rain returns.

"Just using a sprinkler is not enough," Dube said.

Greg Stanley • 612-673-4882