The Greenwood wildfire burned down millions of trees last fall as it swept through nearly 30,000 acres of northern Minnesota's drought-stricken woods. Now begins the decades-long process of growing them back.
Contractors for the Nature Conservancy are planting 130,000 trees by hand this month in state and federal forest lost to the fire near Two Harbors along the North Shore. Foresters with the U.S. Forest Service and Department of Natural Resources (DNR) are still surveying the damage in some of the peat lands and most-intensely burned areas.
In addition, the DNR will drop tens of thousands of black spruce, white pine and other tree seeds by plane and helicopter this year to try to bolster their natural regeneration.
The scope of the fire offers a rare reset for Minnesota's woods and a chance to plant more diverse trees to better protect against pests and diseases, said James Manolis, forest conservation program director for the Nature Conservancy.
Dozens of species — mainly white and black spruce and white and red pine — will be planted.
"We need to get trees growing and stabilize the soils," Manolis said.
Nearly all of Minnesota's forests depend on wildfire. Animals big and small, from moose to songbirds, rely on the messiness of natural disturbances to create a diverse blend of young saplings that provide good forage and old-growth trees that offer protection. But the ability to regenerate after something as intense as the Greenwood fire depends on how many nearby trees survived, Manolis said.
"They can do well if there is a seed source," he said. "The problem is that in a lot of these places there isn't."
The Greenwood fire was not among the state's largest. Even in recent history, the Ham Lake wildfire in 2007 burned more than twice as much land — almost all in the Boundary Waters Canoe Wilderness Area. And the Pagami Creek fire in 2011, east of Ely, was three times as big.
What made Greenwood unusual is that it burned intensely hot. Extreme drought dried up peat lands that had been building for centuries just as an outbreak of the spruce budworm had killed off vast stands of balsam fir trees. Those dead trees and vulnerable peat fueled an uncommonly severe fire, said Jason Bushmaker, forester for the DNR.
In the late fall, the DNR took aftermath photos by helicopter, which show the expected small green stands of surviving trees surrounded by the larger black scorches of the dead. Surprisingly, the photos also showed a great deal of rock.
"That's interesting because it means this fire burntdown all that organic material to expose rock," Bushmaker said. "That organic material is the ground the trees are growing in."
The loss of soil and duff has left the roots of surviving trees exposed, with nothing to anchor them. Even slight gusts of wind have knocked them over, he said.
The sites of the state's other large fires, including Pagami Creek and Ham Lake, typically got a fair amount of natural regeneration from seeds that spread from surviving trees, said Anna Heruth, silviculture program forester for the DNR.
"We're hopeful that's what will happen here, but it was so intensive we're not sure what to expect," she said.
The DNR will watch throughout the summer — from the air and up close on the ground — to see how aspen and other upland trees are recovering or if grasses are moving in to take over, Heruth said. In the meantime, they'll continue to drop seeds and replant trees to ensure they have a chance to regrow.
It's an open question how long forests will take to recover.
Bushmaker said he'd like to see young trees taking root within three years. If after five years there's still not much new life, the DNR may have to rethink its strategy, he said.
The Forest Service is still assessing the condition of its roughly 10,000 acres that burned. Much of it was in the swampy peat lands, dominated by black spruce and tamarack. Those lowlands are fire dependent as well, said Kyle Stover, district silviculturist with the agency.
"We're going to spend a lot of time this summer checking on where soil conditions are so severe that they really need some help," he said. "There are places where the fire burnt feet of peat and some places where it just burnt the surface."