Northern Minnesota forest recovering from May wildfires, but lakes could suffer for years
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More than a month after the Camp House Fire erupted near the small town of Brimson, the devastation is still striking along Highway 44. Trees look like giant blackened matchsticks. All that’s left of many of the more than 100 homesteads that dotted the wooded landscape here are a few charred stone foundations and chimneys.
But step into the forest, and it's easy to see the signs of life returning. Plants like ferns and big leaf alder are a vivid green, sprouting out of the blackened soil.
“Almost universally, everyone’s surprised at how fast vegetation comes back,” said Jason Butcher, an aquatic biologist for the Superior National Forest, and part of a team that assesses the extent of damage caused by a wildfire shortly after it burns, and whether any treatments are needed to mitigate the damage.
Another member of this team, soil scientist Dave Morley, digs a shallow hole in the forest floor to analyze the health of the soil, in a spot not far from where the wildfire hopped across the highway. It’s one of the areas where the fire burned the hottest. A giant white pine tree nearby has been torched completely black, its bark and needles gone.
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But while crumbling a handful of dirt in his hand, Morley says the rich soil looks healthy. “We still have pretty much the same soil structure that was here prior to the fire,” he said.
The Camp House Fire burned fast, driven by ferocious winds. Most of the heat stayed up in the crowns of the trees. When a fire burns hot along the ground, Morley says it cements the soil together. That makes it hydrophobic, meaning water will run off rather than soaking in.
That can be especially problematic in steep areas, where rains after a fire can cause severe erosion and wash big loads of sediment into waterways.
“We’re not seeing those indicators that the site burned really hot at the soil level. So we would anticipate that over time, these are going to recover. We probably won’t need to actively do any kind of follow up treatment in these areas,” Morley said.
Protecting water quality
Much of the treatment work is focused on restoring the forest land where firefighting crews used bulldozers and other equipment to dig the fire lines that helped contain the fire.
At a site near where the fire burned over the Cloquet River, the soil along a section of fire line has been recontoured with an excavator. Trees and brush that were cut to help stop the fire are now spread on top of the gap in the forest, to provide shade and catch water.
The goal here is to help restore the forest land while also protecting nearby waterways.
“So we repair those the best we can, with the whole idea being that we keep the sediment out of the water and the nutrients that go along with it and that are attached to those sediments,” said Butcher.
The work is not only aimed at protecting the pristine waters, but something vital that grows in it — wild rice.
“It’s an indicator of good water quality, and it is sensitive to things like different nutrient levels and acidity,” Butcher explained.
Wild rice is also an important cultural resource to the Ojibwe in the region.
Fire officials were especially concerned about one popular wild rice lake named Breda Lake. Locals and Ojibwe band members from the area paddle canoes down a small stream called Petrell Creek to access the lake and harvest the rice.
The Camp House Fire burned hot along the creek. Butcher pulls up a picture on his phone showing the riparian area along the stream scorched black.
But just a couple weeks later, grass alongside the stream is lush and bright green, nearly two feet tall. The only indication of the recent fire is a scorched sign post.
Butcher expects minimal impacts to the stream here. Runoff is slow in the flat floodplain. The rapidly growing revegetation should capture most of the nutrients before they run off into the creek.
But elsewhere in the burn area scientists expect the fire to have a more negative impact on lakes and rivers.
Standing at a boat landing on Salo Lake, hydrologist Luke Rutten points to a patchwork of burn patterns along the opposite shoreline, while a family of loons calls from the center of the crystal clear lake.
In some areas stands of white and red pine were scorched black. But interspersed among the burned patches are groups of aspen and other trees untouched by fire, their leaves still bright green.
“You can look across and see slopes that are revegetating,” said Rutten. “But there’s still ash and fine sediment that’s available to get washed into the lake from a thunderstorm. You get a fairly intense rain on that slope, you're gonna wash something into it.”
That’s what researcher Chris Filstrup found four years ago, when he studied how lakes responded to the Greenwood Fire, which burned more than 40 square miles of forest near Isabella, about 20 miles from here.
Filstrup studies lakes and streams as a limnologist at the University of Minnesota's Natural Resources Research Institute in Duluth.
His study of 15 lakes found they became a lot murkier after the fire, with more sediment, and more nutrients, mainly phosphorus and nitrogen, that washed in from the burned landscape. While such nutrients might be good for your garden, they’re not good for pristine lakes like these.
“In lakes, more nutrients is a bad thing because it can lead to things like low dissolved oxygen in the water that can create fish kills. It can lead to harmful algal blooms and cyanobacteria blooms. So we were really concerned that these waters were heading in the wrong direction,” Filstrup said.
And Filstrup has found that increased levels of nutrients and sediment have remained in the lakes in the years after the fire.
“And so our thought was that [a major wildfire] may be enough of a disturbance that you’re going to flip a lake to a totally different turbid, brown, algal bloom dominated state, that’s going to persist for quite some time.”
Filstrup plans to continue to monitor the lakes around the Greenwood Fire. He also plans to study three lakes around the Camp House Fire, including Salo Lake.
Since the Camp House Fire burned less intensely than the Greenwood Fire, which burned late in the summer instead of spring like this year’s fires, he’s curious to see if the water quality impacts are also less severe.
He’s also planning to expand the study to also look at mercury levels in the lakes. Other studies in the western U.S. have found that high levels of mercury, which is toxic to humans and fish, have washed into lakes and rivers following major fires.
With more nutrients also washing into lakes, the concern is that mercury could more easily be converted into the toxic form of mercury that accumulates in fish tissue. Eating fish contaminated with the toxin can cause neurological damage, developmental problems in children, and cardiovascular issues.
“What we’re hypothesizing right now is that those conditions in the lakes will lead to more production of methyl mercury from those higher loads of mercury, and when you have higher concentrations of methyl mercury, that’s the toxic form that people really get concerned about,” Filstrup said.
Filstrup hopes his work will help build models to help land managers and tribes make better decisions about lake and forest management after a wildfire, and protect these precious natural resources for future generations.
