Aspen, Minnesota's dominant tree species, stands for more than autumn

There's gold in Minnesota's hills, and in October that gold is aspen.

The most prevalent of Minnesota's 52 native tree species, aspen's amber hues are the perfect backdrop for autumn's fiery maples, orange oaks and verdant evergreens.

Yet aspen is prized for other reasons, too. It is the species that Minnesota's pulp, paper and engineered wood industries use the most, and by a large margin. Aspen forests are also important wildlife habitat. Aspen stands provide food and shelter for deer, bear, marten, songbirds and many other species. Upland bird hunters also prize aspen. These golden coverts are favored stomping grounds for those who pursue ruffed grouse and woodcock.

What follows are four different views on aspen, one each from an upland bird hunter, wildlife specialist, independent logger and university forest ecologist. Together, their words, which have been edited for clarity and length, speak to a species at the heart of Minnesota's outdoor recreation, wildlife conservation and forest economy, and one whose future appears threatened by climate change.

Matt Soberg

Upland bird hunter and hunting magazine editor

Aspen is important to me because it is so important for woodcock and ruffed grouse. Iconic as a habitat species, aspen is a key food source for ruffed grouse in autumn and when snow carpets for the forest floor.

When I am scouting new areas to hunt I am always on the lookout for aspen. Aspen stands that look almost impenetrable are the best. In general, trees that have the diameter of a Ping-Pong ball are better-suited for woodcock while trees that have the diameter of a softball are better-suited for grouse.

My favorite fall activity, hands down, is following my English setters through young aspen stands so thick you can't throw a football through them, all in the pursuit of the American woodcock. Mid-October is the best time to hunt woodcock. If you synchronize your hunting with the fall migration, you can experience more action than you can handle.

We upland bird hunters typically harvest more ruffed grouse than any other state because aspen is so abundant in Minnesota. What we have in our own backyard is often undervalued and underappreciated.

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Meadow Kouffeld

Former wildlife manager and current natural resources instructor at Itasca Community College

Aspen has existed in North America for at least a million years. Therefore, it is no wonder so many wildlife species depend on aspen during some point of their life.

Initially, young aspen stands are composed of thousands of whippy stems per acre that have regenerated naturally via root-sprouting following a wildfire, clear-cutting or other major disturbance. These young trees provide high-protein browsing during fall and winter for large ungulates such as deer and moose. Many bird species use dense aspen stands for nesting and rearing their broods. The wood thrush, for example, is a species associated with old-growth forest but relies on young aspen for fledging its young during their first summer. Migrating woodcock, warblers and other birds also use dense young aspen stands. Even bears use young aspen. I have seen bears bend over young trees so they can strip and eat the leaves.

As an aspen stand grows beyond browse height, it begins to thin itself. During this time, shrubs take hold in the understory, thereby adding a layer of structural complexity that provides physical protection for drumming grouse, snowshoe hares and other important prey species. Aspen leaves remain an important food source for ruffed grouse during this time.

As aspen matures, the buds that form at the end of branches become favored food. The buds on male trees are so rich in protein that in winter a grouse can get all the nourishment it needs from feeding just 30 minutes or so. This efficiency is important. It minimizes the bird's exposure to predators and maximizes the time it can safely conserve energy in a snow roost.

As aspen trees reach the end of their life — typically 60 to 80 years in the Upper Midwest — they begin to decay, thereby providing homes used by a wide variety of cavity nesting species such as pileated woodpeckers, pine marten and even wood ducks. Old aspen stands also change in composition. Balsam fir becomes more common, and this provides important thermal cover for whitetail deer in winter.

An aspen tree continues to provide ecological benefits once it dies or is blown over — a drumming log for a grouse, a microclimate for amphibians and, of course, slowly returning to the soil in the form of nutrients. An aspen forest composed of several different age classes provides the most benefit to wildlife.

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Scott Pittack

Independent logger and small business owner

I'm a logger, so aspen is a critical species for me. It is as important as white pine was in the past. It's just that valuable.

I operate a small business northeast of Grand Rapids, and we cut from 14,000 to 16,000 cords of timber each year. Most of our production — a good 50 to 70% — is aspen. It's the species that keeps us going. Aspen to a large degree is what brings in the revenue to support my wife, who does the books; my son, who operates a tree harvester; and three or four other employees, who skid timber to the roadside and truck it to the mills.

Aspen is versatile, and we work hard to maximize the value of each tree. Some aspen is trucked south to McGregor, Minn., where it is turned into pallets. Some goes north to International Falls, where the Boise mill converts it into paper. We also haul aspen to the Sappi plant at Cloquet, a state-of-the art mill that converts trees into a dissolving wood pulp that U.S. and world manufacturers use to make clothing and other items you wouldn't expect. And, of course, some of our aspen is used locally at the UPM Blandin paper mill in Grand Rapids.

While I believe there is plenty of aspen in Minnesota, I do have concerns. Most relate to the production side of the industry. Traditionally, much of the wood we harvest has been converted into high-quality paper used by magazines and catalog publishers. Today, more and more publications are going online. People can read magazines and browse through catalogs without ever touching a piece of paper. To that end, our industry needs to stay focused on finding new markets and new products. Aspen has a lot of potential uses: biofuels, chemical products and new construction materials. The key is being able to develop and sell these products in a profitable way.

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Lee Frelich

Director of the University of Minnesota Center for Forest Ecology

When I view Minnesota's aspen forests I see them through a lens that begins before European settlement and focuses far into the future. Aspen was always present in Minnesota but it was nowhere as abundant as it is today. Aspen existed in the parklands of the northwest and in small patches elsewhere, but it didn't take off until European settlement changed the landscape in two significant ways. First, for a brief time, wildfires became more common, following widespread timber harvest and slash-and-burn agriculture. Second, wildfires became far less frequent because there was a need to suppress them.

Aspen prospered in this post-settlement environment. Aspen does well in direct sunlight and when the soil has been disturbed. Both conditions existed broadly in the wake of widespread clear-cutting and slash-burning that began in the mid- to late 1800s and continued into the early 1900s. As a result, fast-growing aspen out-competed other tree types and became the dominant species it is today.

Yet aspen's future does not look good. Our climate is changing and aspen is not well-suited for what's ahead. Virtually all climate models predict Minnesota will experience warmer winters and summers, with much of Minnesota having a climate similar to southern Iowa and the Boundary Waters Canoe Wilderness Area having a climate more similar to Granite Falls.

Aspen won't do well in this environment because summer heat waves and extended drought will reduce moisture in the ground — moisture that aspen need for transpiration, which is the process of water going from roots to leaves and eventually into the atmosphere as vapor. Trees fail as transpiration ceases. We are already seeing the impact of heat intolerance on birch trees along the North Shore, where many have died or are dying. In time aspen stands won't grow back as they do now either.

In a historical context, Minnesota's aspen forest was limited, became dominant and now seems destined to shrink. The exception will be the boreal forests of the far north. When major wildfires blackened large acreages in 2006, 2007 and 2011 in the far north, conifers did not come back as they always have. In the wake of wildfire, we witnessed a change: more aspen, less conifer.

C.B. Bylander is a freelance writer. He lives near Baxter, Minn.