Eastern hemlock (Tsuga canadensis), one of Minnesota’s most imperiled trees, has been unable to keep up with environmental changes. It was rare even before the era of unrestrained logging and slash fires, but its future in Minnesota is even more tenuous now.
The state’s largest reported hemlock stand, nearly 5,000 trees of all sizes, was near the town of Paupores in St. Louis County. In 1912, about 8,000 hemlock railroad ties were cut from this stand. To protect the remaining trees, a state park was proposed for the site. The Moose Lake-Cloquet fire of 1918 intervened, destroying all but a few individual trees, which eventually died.
Currently there are around 10 known hemlock stands in Minnesota. The largest consists of 14 mature trees and fewer than 50 juveniles and seedlings. Other sites may have only a few trees, with little if any reproduction.
Eastern hemlock is a species of stable, old-growth forests. Reproduction takes place only where there is deep shade and moist, undisturbed forest soils. When forests are cut, sunlight warms and dries the soil, giving the advantage to other tree species. This may be one reason hemlock didn’t fare well in Minnesota during the logging and land clearing in the early part of the 20th century. Predation by deer and porcupine may have contributed to the decline.
The future might not look much better for hemlock in Minnesota. We know it needs a moist climate, especially in autumn, and some climate change predictions posit that Minnesota may get warmer and drier in the years to come. But other forecasts suggest a warmer and wetter climate, which would be more hospitable to hemlock.
The composition of Minnesota’s future forests, in an era of global warming, will largely depend on each species’ adaptations. Trees evolved exquisite adaptations over millennia. But the climate changes that trees face today are happening quickly, perhaps within only one or two tree generations, far too quickly for trees to change their strategy. It will be the most rapid, large-scale change to Minnesota’s forests since logging and settlement, when grand stands of towering pines fell and were replaced by legions of aspens.