Minnesotans For Sustainability

 

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Blowdown, burns change
Boundary Waters Growth patterns

Lee E. Frelich
*
August 25, 2003



Human Impact
Blowdown 1999
Prescribed Burns
New Forest Mosaic


 

Regarding the July 4, 1999, blowdown in the Boundary Waters Canoe Area, new policies of prescribed burns and old policies of fire suppression:

For centuries before European settlement, forests in the Boundary Waters Canoe Area Wilderness were dominated by pines: jack pine, red pine and white pine. Aspen, paper birch, black ash, black spruce, balsam fir and white cedar were also present, but they were of minor importance.

Jack pine was the most abundant, and it grew in rocky areas that were burned by severe crown fires every 50-70 years. Its cones remain closed for years until the scales are opened by the heat of fire, releasing seeds that rain down on the forest floor and regenerate the same species after the fire.

Other areas had less-frequent crown fire, every 150-300 years, because large lakes interrupted the flow of fire across the landscape.

Instead of severe fires there were surface fires. White and red pine dominated here, including the central Boundary Waters area around Ely. Many of the mature white and red pines survived the surface fires, and their seeds were able to germinate and grow in the understory that was kept clear of brush and invading spruce, fir and cedar, which would otherwise have outcompeted the pine seedlings. Then came European settlement and a warming climate.


Human Impact

Between 1890 and 1970, half of the forests within the wilderness boundaries were logged. Pines were unable to reproduce because of a lack of a seed source and competing brush, and pines were replaced with a new forest of aspen and birch.

In the unlogged parts of the Boundary Waters, the past century has seen fewer fires because of the changing landscape mosaic surrounding the wilderness, a warmer, wetter climate and fire suppression. As a result, very few new stands of young pines were created after 1910. In the absence of fire, spruce, fir and cedar have invaded underneath the pines.


Blowdown 1999

This set the stage for the great blowdown of July 4, 1999. Mature trees were much more likely to blow down than seedlings and saplings in the forest understory.

In the second-growth forests, mature birch and aspen were felled by the wind, leaving behind an understory of balsam fir and shrubs such as mountain maple, hazel and dogwood to take over. In the forests that had never been logged, the old pines fell and the understory fir, spruce and cedar were free to grow.


Prescribed Burns

Finally, the Forest Service started a prescribed burn program to reduce the fuel load within the blowdown. The fires completed so far have been very successful at reducing the 1-to-3-inch-diameter woody fuels that are paramount in determining fire behavior and intensity. Because there are tons of these 1-to-3-inch-diameter fuels on every acre, the prescribed burns have reached an intensity normally only attained by wildfires during a drought.

Three Mile Island in Seagull Lake was burned last September. In the charcoal left behind, relatively few pine seedlings are germinating compared to the historical forest. Many of the big pines which dated from previous fires in 1801 and 1864 were killed in the blowdown, and any seeds still in the cones were consumed by the fires, since they were down in the midst of the flames.

However, there are a handful of jack pines on the island that were snapped off at midcrown by the wind, and the lower parts of the crowns were still alive, produced cones between 1999 and 2002, and were still vertical and high enough to be scorched, but not consumed by the flames. The seeds of these pines fell on the forest floor last September and began to germinate in May.

Several groves of red pines along the lakeshore had 50 percent survival after the windstorm, and 50 percent of those survived the fire. Their seeds will rain down on the forest floor in decades to come. Also growing on the island are paper birch and aspen seedlings, from a number of trees that were bent but not broken during the windstorm, and from the sprouting stumps and roots birches and aspens whose above-ground trunks were killed in the fire.


New Forest Mosaic

Within the great blowdown of 1999 we now have a mosaic of three different forest types. Fir and shrubs in the second-growth forest; fir, spruce and cedar in the unlogged forest that has not burned; and birch with a few pines in the unlogged areas that have burned. Outside of the blowdown the second-growth is also succeeding to fir and shrubs and the unlogged forest to spruce, fir and cedar. Succession is taking those forests along the same route of change as forests within the blowdown, but more slowly, since the pines are dying gradually rather than being mowed down all at once by high winds.

Thus, the Boundary Waters is becoming a mosaic of birch and aspen mixed with conifers, and spruce-fir-cedar forests. Species that for centuries were dominant -- the pines -- are now a minor component of the forests. Those that were minor -- birch, aspen, fir, spruce and cedar -- are now becoming dominant.

It's a much different forest than that witnessed by the fur traders during the 1800s, and there seems to be no way for the forest to regain its historical status.

Lee E. Frelich, a forest ecologist with the University of Minnesota Department of Forest Resources, is monitoring the forest's recovery on Three Mile Island in the Boundary Waters Canoe Area Wilderness.
______

* Courtesy of Duluth-News Tribune.
Point of View, August 25, 2003
See original at < http//www.duluthsuperior.com/mld/duluthtribune/news/opinion/6612553.htm >.

 

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