Interview: Understanding Minnesota’s Changing Forests with Professor Lee Frelich

Lee Frelich

Lee Frelich

By Brock Berglund

Lee Frelich is Director of the University of Minnesota Center for Forest Ecology. In an interview with Brock Berglund of the Chapter’s Communications Committee, Professor Frelich talks about Minnesota’s unique forest ecology, the invasive species which threaten it, and how Minnesota’s wilderness will change in the next century.

Ecologically, Minnesota covers a unique space, occupied by three distinct biomes. In the South and West lie prairies, in the East, temperate deciduous forests, and in much of the North, the idyllic boreal forests which make up the Boundary Waters Canoe Area Wilderness (BWCAW). However, climate change threatens to throw off the delicate balance between these three biomes and completely extinguish the boreal forests from our state—leaving behind a vast expanse of oak savannah. Professor Lee Frelich discusses the threat to our boreal forests, as well as other interesting topics in today’s interview.

Please, tell the readers a little about yourself.

Currently, I am Director of the University of Minnesota Center for Forest Ecology. Reading classic books such as John Curtis’ The Vegetation of Wisconsin and Sigurd Olson’s books like The Singing Wilderness, caused me to decide on forest ecology as a career when I was only 12 years old. I received a PhD in Forest Ecology from the University of Wisconsin-Madison in 1986 and moved to Minnesota in 1988. Research interests include large-scale fires and windstorms, invasive species, and climate change impacts on forests.

What is forest ecology?

Forest ecology is the study of structure, species composition, and function of tree-dominated ecosystems. In other words, the forested landscape includes trees of many sizes, ages, and species, in various patterns across the landscape. A forest ecologist studies what these patterns are, how they were created, what the implications are for wildlife and ecosystem health, and how they might change in the future as environmental factors, like human use of the forest and climate, also change.

Invasive earthworms are a global phenomenon that scientists have identified as one of the top environmental issues…

Could you talk about your current research and why researching the forests are important to Minnesota?

My students, colleagues, and I have hundreds of plots across the landscape where trees have been tallied and revisited several times over the last 20 years, to see patterns of growth and mortality of various species of trees and native plants. We also record histories of fires, storms, progress made by invasive species, effects of grazing animals like deer, and temperature. We compare subsets of the plots— for example, old growth versus young, logged versus unlogged, burned versus unburned, or warm plots versus cold plots. These comparisons allow us to obtain a comprehensive picture of change caused by many influential factors—over the region and over time. Without such careful observations and analyses there would be no way to explain why the forest is changing or to predict how it might change in the future.

Why study invasive species, especially earthworms?

Invasive earthworms are a global phenomenon that scientists have identified as one of the top environmental issues, due to the way they re-engineer ecosystems by changing the structure of the soil, usually stripping away the leaf litter or duff layer and compacting the soil. This results in in many important ripple effects that affect all other species in the ecosystem, as well as ecosystem services to society. The cascade of effects includes nutrient and water availability, water quality, and even spillover effects into cropland adjacent to forests. Invasive earthworms facilitate other invasive species in a cascade of effects known as “invasional meltdown.” The invasive earthworms affect everything about the future: what species of trees and wildflowers will be able to live in the forest, which in turn determines what species of wildlife can live there.

How are earthworms changing Minnesota’s boreal forests?

They are not just changing boreal forests, they are changing all forests in Minnesota. In southern Minnesota the earthworms are reinforcing the impact of overabundant deer, changing forest plant communities—for example, replacing Trilliums with grass-like sedges. Looking specifically at Minnesota’s northern forests, the earthworms are rapidly invading the landscape and working in concert with a warmer climate to help red maple invade the boreal forests of spruce, fir, and pine. By removing the leaf litter, earthworms create perfect conditions on the forest floor for germination of red maple seeds. Leaf litter also insulates the soil during summer, keeping it relatively cool and moist, and the absence of leaf litter in areas invaded by the worms also make northern forests on shallow rocky soils—like the Boundary Waters Canoe Area Wilderness (BWCAW) and the north shore—more susceptible to droughts, which have increased in frequency in recent years and are predicted to occur even more often with the warming climate.

Over the next century Minnesota could lose the entire boreal biome…and with it one third of all native plant and animal species.

How has climate change affected Minnesota’s forest ecology?

We are just at the beginning of climate change. Although major impacts from earthworms are already evident, most of the impact of climate change will occur over the next several decades. However, the warming that has already occurred and increasing drought frequency is allowing temperate tree species to invade the boreal forest of the BWCAW, and causing higher mortality of tree species adapted to colder climates. This tree mortality is complex, involving storms, fires, droughts, earthworms, and greater susceptibility of trees to insect pests and disease.

What will Minnesota’s forest ecology look like in the next century?

I am betting that we will see unmitigated climate change (but hope that I will be proven wrong). This would mean much less forest and lots more bur oak savanna! Over the next century Minnesota could lose the entire boreal biome (we have three main biomes; grassland, temperate deciduous forest, and boreal forest), and with it one third of all native plant and animal species. Wildlife species such as moose and black-backed woodpecker that live in boreal habitats could also disappear along with the boreal forest.

What else should we be thinking about regarding this research?

It is important to reduce CO2 emission as much as possible. Although significant climate change and impacts on forests are already in the pipeline, a smaller magnitude of climate change will lead to smaller impacts on the forest. For example, with a large decrease in CO2 emissions over the next few decades, we might see only a few degrees rise in temperature, and persistence of some boreal forest mixed with patches of temperate forest in the BWCAW. On the other hand, a business as usual scenario will lead to major changes, loss of the boreal biome, and conversion of the forest to oak savanna.

What can readers do to help protect Minnesota’s forests?

The synergy between invasive species and warming climate is huge. As a society we need to think a lot more about tree diseases and insect pests like emerald ash borer, and underground invaders like earthworms, and keeping them in their native habitats and not moving them to new continents. At the same time, doing everything possible to reduce greenhouse gas emissions will be very important. Climate adaptation planning to help forests contend with warming that is already in the pipeline, and that takes into account the interactions with invasive species and other human impacts like fragmentation is also needed.

Get involved! To learn how you can help protect and preserve Minnesota’s forests, contact our Forests and Wildlands Committee or come to our New Volunteer Night.

Writer, Brock Berglund

Writer, Brock Berglund

Brock Berglund is a volunteer with the North Star Chapter’s Legal Committee and Co-Chair of the Communications Committee.


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