The Pagami Creek fire burns in northeastern Minnesota on Tuesday, Sept. 13, 2011. MPR Photo/Derek Montgomery

The Pagami Creek fire burning in the Boundary Waters is the biggest the area has seen in more than a century. But historically, big forest fires used to be commonplace in that area. In fact, they're part of a natural process that rejuvenates the ecosystem.

Lee Frelich, a forest ecologist at the University of Minnesota, spoke with MPR's Morning Edition about the role fire plays in a forest.

Cathy Wurzer: What do you find in the aftermath of these fires?

Lee Frelich: You find that a lot of trees within the fire perimeter are still alive and they are the seed source for the future forest. You find areas that are as black as a moonscape and burn down to bare rock. It's very interesting the things you see pop up in the fire. We'll be having several Ph.D. students at the University of Minnesota looking into the aftermath of the big fires we've had in recent years.

[[header: Wurzer: There have been several fires in the last decade. What is the frequency of these types of fires?

Frelich: It looks like the frequency of big fires is increasing in the last decade. But if you look back historically for the last 300 years during the 1600s, 1700s, 1800s, a fire like the Pagami Creek fire occurred about once a decade on average, and then during the 1900s there were hardly any fires of significant size in the Boundary Waters, and now we seem to be returning to a period with big fires again, so I think the anomaly is the 1900s when we had fewer fires.

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Wurzer: Does the climate factor into why we're seeing more warm, dry weather?

Frelich: With a much warmer climate that we're experiencing in northern Minnesota today, and the uneven distribution of rainfall where lots of rain falls in a short period then there's several weeks where no rain falls, I think this new pattern of extreme droughts and floods will be conducive to fires because you get those long gaps without rainfall. That's more characteristic of the climate you see on the great plains than a forest climate which tends to have more even rainfall. So it may be an indication that the savannahs and prairies of the west are beginning to shift into Minnesota.

Wurzer: Should more have been done initially to put out the fire that started by lightning in the Pagami Creek area?

Frelich: That's almost impossible to judge. This is one case where there's no 20/20 hindsight. You never know if they would have been able to put it out when it was small or if some tiny little pocket would have survived that was unnoticed and would have blown up later. It's just difficult to tell what the alternate trajectory would have been.

Wurzer: Why are fires good for forests?

Frelich: These fires are necessary because the species of trees that grow in the Boundary Waters are fire dependent. Jack pine and black spruce, for example, have closed cones that don't open unless there's a fire. Even the birch and aspen, their roots survive and they sprout after a fire. In fact, in the absence of fire, spruce, fir and cedar tend to take over and you have a more homogeneous landscape. When you have these fires occurring in different places across the landscape then you get a mosaic of forest in different stages of succession and there are species of wildlife that use all different stages. Moose would probably benefit from having a lot of younger forests. We think these recent fires will have a lot of young birch saplings, and that's one of the favorite foods of the moose. So having a mixture of different forest ages on the landscape is something that will happen if fires occur on a regular basis over time.

Wurzer: It's been four years since the Ham Lake fire. What are we seeing in that area now?

Frelich: There are birch saplings and aspen saplings. In a few places there are a few jack pines. It appears that white pine was hit very hard by the combination of blow-down followed by fire, and white pine is virtually exterminated, unfortunately. There's a little bit of red pine regeneration, a little bit of spruce and fir, but basically there's a lot of birch and aspen and some places there's a lot of shrubs too, like blueberries and raspberries. It's about four years after a fire that's the best berry-picking, actually.

Wurzer: Are there any ecological dangers at all from a fire like this?

Frelich: The only ecological danger is if some invasive species could take advantage of the fact that the forest has been disturbed and jump in at that point and take over. That's why it's important to keep invasive species away from the Boundary Waters so things like buckthorn, garlic mustard and Canada thistle have less of an opportunity to jump in. As long as native species are able to take advantage of them, it's generally a good thing for managing a healthy ecosystem.

(Interview transcribed by MPR reporter Elizabeth Dunbar)