Forest evolution

Climate change is certain to create new physical environments for forests. Forests will certainly take on new forms. What, exactly, those forms will be has researchers and resource managers thinking.

Forests have been evolving for millennia. The Lake States were once covered in ice and the Great Lakes themselves were formed through glacial action. The current forest cover was created post-apocalyptically following the massive over-cutting and sweeping wildfires from a century ago. And the forests are now in the early stages of another rapid, and sweeping, change. 

Major shifts in climate over the next 50-100 years will have profound effects on the north woods. Our grandchildren will not hunt, fish and camp in the same forests that we enjoy today. Forests have much to do with our quality of life and sense of place. These things will change, too. 

There is no credible debate about whether or not the Earth’s climate is undergoing change at an unprecedented rate. And, there is no doubt that these basic environmental underpinnings will alter forest composition, structure and function. However, predicting precisely how forest types will change is more difficult, which contributes to uncertainty.

Although this winter and last winter seem counter to these prediction trajectories, they are part of the normal expected variation in a warming global climate. We will see fewer long, cold winters into the future. Summers will be hotter and drier, causing stress for trees and forests. Winters will grow warmer and wetter. Those plants and animals that have extended cold winter requirements will not fare well. Seedling germination may be disrupted. The ground rules of survival won’t be the same. 

Wetter springs, with more intense and frequent rainfalls will flush the rivers and streams at unprecedented levels. City storm drains will regularly be overwhelmed. Culverts and low bridges will be increasingly likely to fail. Health departments will learn to cope with new challenges. 

More freeze-thaw cycles during the winter will stress root systems and increase mortality among those dormant wildlife that need the extended mantle of protective snow cover. Loggers may need to invest in equipment modifications when the ground no longer freezes long enough, or hard enough, to permit conventional winter timber harvests. Snowmobilers will find fewer places, for shorter periods of time.

Under some climate scenarios, the Lake States climate is expected to migrate into something similar to that of Arkansas by the end of the century. Some of our tree species may not be able to adapt to the new regimes. Sugar maple may be one of the losers, along with many of our boreal and near boreal species, such as paper birch, tamarack and black spruce. Imagine the north woods without sugar maple. 

These predictions are not merely the whimsies of fanciful doomsday purveyors. The climate data and projections are about as solid as science can get. There is simply no doubt within the scientific community. The early stages of forest change are already being documented. The forest has been stirred. 

Boreal conifers in northern Minnesota now have red maple and oak in the understory. Transects cutting north and south across parts of Wisconsin and the Upper Peninsula are revealing altered tree species composition. The mountain pine beetle has followed the warming in northern Canada to cross from lodgepole pine to pure strains of jack pine. Boreal forest fire frequency has increased. Timing of the flowering and leaf-out among some tree species is changing. The same is true among understory flora. Some of our current forest areas may no longer be able support trees, which is fine with savanna and barrens enthusiasts. Moose populations are in trouble. 

Of course, climate is not the only agent of change impacting forests. Deer depredation, forest parcelization, exotic species, and the loss of forest industry all work together, with climate change, to create an environment particularly harsh to current forests. Many times, two or more of these agents working together have a stronger synergistic effect than they would separately. However, climate change will become an increasingly important underlying factor for all of these agents. Scientists suggest changes will pick up a lot of steam by 2050.

As forests change, so will forest functions, such as habitat characteristics, hydrology, recreation, understory species, and risks to endangered species. Cycles involving water, temperature, humidity, nutrients, organic matter, soil chemistry and other abiotic dynamics will affect the biotic components. 

The scientists who work with computer models constantly add new data and program designs as they come along. Technology will help models become increasingly robust and, perhaps, more precise in their predictive ability. Forest researchers are monitoring changes on the ground. The body of literature is growing, even though the forests are in the early stages of responding to climate change. 

Many of us will not be around after 2050. However, we’ll be leaving an indelible legacy on the forest of the future. 

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