Could the boreal forest of the Boundary Waters Canoe Area Wilderness change to a more temperate hardwood landscape or even a grassland savanna? If so, when? According to Lee Frelich, Director of the University of Minnesota Center for Hardwood Ecology, that scenario is not only probable but possible within a century. Frelich and U of M Forest Ecologist Peter Reich have just published a paper which concluded the effects of climate change could result in warm, dry climate that would, likely by 2100, create a climate similar to Iowa.
Frelich says a major change in the northern forest is a certainty and with a warmer climate comes invasive species.
Frelich: Earthworms, which are not native in Minnesota, eat the litter layer on the forest floor, and usually there’s a multi-year accumulation of litter. When that litter is present, it insulates the soil and keeps it cooler and moister throughout the summer. So, as the worms chew their way across the state and eliminate this litter layer on the forest floor, they’ll make the soils warmer and dryer at the same time as the climate is getting warmer and causing more evaporation. And then, the deer come along and they like to eat the seedlings of certain species of trees. Some of those tree species are ones that would be expected to do well in a warmer climate, such as white pine and red oak. These are species of trees that in northern Minnesota would do better in a warmer climate, but if they’re unable to reproduce because the deer eat all of their seedlings, then they won’t be able to increase in abundance.
Frelich says the 5 million plus acre Quetico-Superior Ecosystem is among the most endangered in the world.
Frelich: The Quetico-Superior Ecosystem is fairly close to the prairie forest border. In other words, we have prairies in the western part of Minnesota all the way out to the Rocky Mountains. So, we’re right on that boundary, and places that are near boundaries are more sensitive to climate change then places that are way in the interior. It’s right near the boundary that you expect the biggest changes. And, it’s very possible that by the end of this century a climate that will support forest will no longer exist over the Quetico-Superior Ecosystem. The Ecosystem is mostly on very shallow soils that are shallow to bedrock. Shallow soil systems are also vulnerable to climate change, because if the water balance changes just a little bit, if there’s more evaporation than precipitation in a warmer climate and the soil dries out, those shallow soil systems are also much more likely to change than places that have a deep, loamy or silty soil. The Boundary Waters and Quetico Provincial Park and areas like that only hold a little bit of water, so there’s not much of a store of water for trees to get through a period of drought.
The northern forest vegetation is more sensitive to a changing climate than most because it lies close to the prairie grasslands.
Frelich: A warm and dry climate in shallow soils favors grasses, shorter grasses, cactus of various types, stunted trees, bur oak and juniper and so on, which could be kind of bonsai-like. A good example of a place like that is Gneiss Outcrops Natural Area, which is down near Granite Falls in west-central Minnesota. There’s a big outcrop there of igneous rock, which is kind of analogous to the types of rock outcrop you have in the Boundary Waters, but it’s a much warmer and drier climate and the vegetation on top of there is two species of cactus and things like little blue stem and other short grasses and stunted trees. That’s the type of vegetation you get on a shallow, rocky soil in a warm, dry climate.
Forests of jack pine mixed with black spruce, quaking aspen and paper birch were a mainstay of pre-European settlement in the area. Those forests were regenerated by severe crown fires with a rotation of between 50 and 100 years.
Frelich: Jack pine and black spruce both have cones that are stored on the tree for years and they don’t open until they’re scorched by the heat of fire, and it’s an adaptation to regenerate after a fire that those species of trees have. Because we’re close to the prairie forest border and our forests are very droughty, these fires are frequent. The fuels dry out enough to support fires fairly frequently compared to fires in further east. Fire has historically been a natural part of these forests. A given area would burn every 50 to 100 years, and actually, in the absence of fire, the forest goes into a completely different stage of development, which has a lot more balsam fir and white cedar. Now, in a warmer climate, of course, there might be even more droughts and fires might become even more frequent, but they might become so frequent that the trees don’t become old enough to bear seeds. You start having fires every 10 years, they won’t be old enough to bear seeds by the time they’re killed by the next fire, and then the vegetation would flip over to some kind of more savannah-like vegetation with scattered trees and a grassy setting.
Several recent natural events have speeded up the change in the BWCAW. The 1999 blowdown as well as the Cavity and Ham Lake fires, to name just three.
Frelich: Big events like big blowdowns and then followed by fires are predicted to become more common in a warmer climate.
But Frelich says that forest managers could put mitigating plans in effect, but it will mean taking a new and different look at current techniques.
Frelich: There’s a limited effect that we can have by changing the management of forests. It’s actually a very difficult problem to adapt forest management to a changing climate. There are some things that can be done to facilitate that change. For example, if it becomes obvious that the boreal forest is no longer suited to the climate, then to allow it to make a transition to temperate hardwood forests like maple and oak or to a savannah, depending on the type of site. If it’s shallow soil it’s more likely to be savannah. To help facilitate that transition to get the best savannah that we can, and we want it to be native species rather than a million acres of buckthorn in the Boundary Waters, for example. You can’t make a spruce tree grow in a climate like Iowa, that’s just an impossibility, and if we try to keep the boreal forest too long, it would just reach point where it would all die very suddenly and then we’d be left with nothing.
For Lee Frelich, major change in forests of the BWCAW is a certainty, and facilitation of a ‘graceful transition’ to native species rather than exotic species is desirable.