Blowdowns were not traditionally thought to be a major disturbance force in the boreal forest. Presumably the mean position of the jet stream during summer is further north during times of warm climate, allowing humid tropical air masses from the Gulf of Mexico to penetrate further north, resulting in warm, wet summers with many thunderstorms that lack dry lightning. Conversely, during colder times, the supply of moisture to northern Minnesota from the Gulf of Mexico would be cut off by the more southern position of the jet stream, resulting in dry vegetation and dry lightning strikes that ignite fires. Disturbance regime change inevitably leads to change in the composition of the forest. Wind without subsequent fire tends to advance succession, by removing competing overstory trees of pioneer species, releasing understory shade-tolerant saplings, such as white cedar, black spruce, balsam fir and to some extent, white pine.
Crown fires tend to lead to dominance by jack pine on poor soils and aspen on good soils.
Bergeron s research shows that this tradeoff between cedar and jack pine species groups has occurred in the boreal forest over the last few thousand years. A third disturbance effect is the double whammy of windstorm followed by fire in the windfall slash. Some rocky areas with an organic moss layer as soil could be burned to bare bedrock. With the current climate, intact forests of aspen and jack pine will continue to regenerate to aspen and jack pine if burned, succeed to shade-tolerant species if blown down, and regenerate to mostly aspen and paper birch if blown down and burned. The scenario may be different, however, if, as many scientists predict, the pace of global warming accelerates in the next few years.