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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

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Vegetation data collection is an ongoing part of old forest characteristic studies. Researchers record the presence of plants such as the wood violet, Wisconsin's state flower. © Don Blegen
Vegetation data collection is an ongoing part of old forest characteristic studies. Researchers record the presence of plants such as the wood violet, Wisconsin's state flower.
© Don Blegen

October 2004

Assessment and study

Research lays the groundwork for understanding and management.

Karl Martin, Natasha Kassulke and Tony Rinaldi

Early research results – comparing old-growth and managed stands
Partners in preservation and production | Changes in attitudes

With patience, we can develop old-growth forests in preserves and other passively managed lands, but can we have forests with old-growth characteristics, and produce wood products from the same land?


Researchers are developing experiments to test how and if this can be done. But to get to that point, they first needed to reach a sound scientific understanding of how old-growth is formed and functions. They also needed to be able to mimic nature's removal of trees while retaining the look and complex ecological workings of old-growth.

It's taken many partners and years of research to lay some groundwork for accomplishing the lofty goal of taking an ecosystem approach toward promoting biological diversity, forest sustainability and economic use of our current forests.

Most of the scientific research on old-growth in this country took place in the Pacific Northwest, but some very good work has also been conducted in forests here in the Great Lakes states. One such study is the managed old-growth work done on the Ottawa National Forest of Michigan's Upper Peninsula.

In addition, the Wisconsin Department of Natural Resources teamed with many others in a cooperative research effort on old-growth forests and their management. Collaborators include the University of Wisconsin, Milwaukee Public Museum, the Forest Products Lab, Nicolet Hardwoods Corporation, the U.S. Forest Service Research Program and national forests.

"The study, initiated in 1993, lasted eight years and got us to this point," explains Karl Martin.

Early research results – comparing old-growth and managed stands

Recent old-growth research has focused on northern hardwoods, and looked at differences between Michigan's Sylvania Wilderness and similar, but younger, managed forests in adjacent Wisconsin.

The soils in old-growth Michigan hardwoods had significantly more, sodium and nitrate ions than those in managed hardwoods of northern Wisconsin. In addition, rain falling through the canopy had higher levels of magnesium and potassium cations. This suggests the managed stands are growing more quickly and cycling nutrients more actively. Another interesting finding: trees like basswood cycle greater amounts of nutrients more quickly than other species.

There are more species of invertebrates than any other group of species in the forest ecosystem. Of these, beetles are most abundant and ground-dwelling beetles perform important functions in forest stands. Beetles are especially important in decomposing woody debris and preying on insect species viewed as forest pests. Somewhat different groups of beetles live in old-growth, managed hardwood stands and managed hemlock stands, but all are important to the forest.

Spiders also comprise much of the living organisms in our forests, The numbers of spiders collected in the leaf litter of old-growth vs. managed stands did not differ significantly, although more species were collected in old-growth stands.

Similarly, old-growth stands had a richer diversity of fungi that decompose wood, though some fungi species were found more often in managed stands.

Old-growth stands also are home to more species of lichens than managed hardwood stands. The managed stands had fewer lichen species capable of fixing nitrogen, an important asset for naturally cycling nutrients for growing trees. Lichens especially associate with standing snags and partially decayed woody debris on the forest floor.

There are other differences and similarities in the plant species found in old-growth and managed hardwood stands. Shrubs like red raspberries and red-berried elders are more abundant in managed stands and are rarely found in the gaps and openings in old-growth forests. On the other hand, sugar maples dominated the woody understory in both kinds of stands and there was little sign of hemlock regeneration in all stands.

Openings created by periodic tree harvests in managed uneven-aged stands developed a multi-layered tree canopy very similar to that found in old-growth stands. By contrast, young unmanaged stands, the small gaps close quickly as treetops spread and shade the forest floor.

As one would expect, the number and particularly the size of fallen logs and limbs is greater in old-growth stands, moderate in managed stands of uneven-aged trees, and lower in stands of even-aged trees. The same holds for large snags (standing dead trees) used by cavity-nesting birds.

Breeding birds show definite preferences for certain forest types. Red-shouldered hawks, pileated woodpeckers and chimney swifts are more abundant in old-growth forests. Blackburnian warblers, northern parulas and red-breasted nuthatches prefer hemlocks. Rose-breasted grosbeaks, downy woodpeckers and black-throated blue warblers are more prevalent in northern hardwoods. Generally, stands with trees of uneven sizes and ages provide significantly more habitat than even-aged stands with trees of the same size.

Some of the individual differences between old-growth forests and managed forests may seem trivial, but old-growth stands clearly provide subtle differences that are important to some species. The combination of soils, insects, fungi, lichens, shrubs, amphibians, birds and mammals found here produce a unique forest ecosystem.

Ideally, we can develop management techniques that allow us to harvest resources from the forests while still creating the habitat conditions that mimic old-growth stands, Martin says. While these forests won't replace natural, old-growth stands, they can provide habitat that sustains many old-growth characteristics.

Partners in preservation and production

Paul West, director of conservation science for the Wisconsin Chapter of The Nature Conservancy, also is interested in creating habitat for species that thrive in old-growth.

Earlier this year, the Conservancy assessed northern hardwoods in Wisconsin, the Upper Peninsula and eastern Minnesota using satellite images. In 2002, the group also identified what it thinks are the most significant places for conserving biodiversity in northern Wisconsin, Minnesota, western Upper Peninsula and parts of Ontario and Manitoba.

"This effort included over 100 experts from state, federal and provincial governments, as well as universities and conservation organizations, and will be used to guide where the Conservancy and its partners work," West says.

The Conservancy also is working at Caroline Lake, located at the headwaters of the Bad River, which empties into Lake Superior. Here, the Conservancy will use forestry practices to create a forest structure and composition similar to that found in old-growth or older forest.

"We'll monitor if certain wildlife species are present and abundant due to the acreage of habitat we can provide," West says. That means, for example, checking for the presence of the black-throated blue warbler or habitat that would support that bird.

Work in old-growth research also is underway at the Kemp Natural Resources Station, a UW-Madison research and teaching facility in Northern Wisconsin. Kemp was once a summer residence for a family in the wooden door business. Old-growth exists at Kemp today because the family did not log timber around its homestead but instead preserved it for their enjoyment. Here, you will find hemlock-hardwood that is 200 to 275 years old.

In August 2000, a strong windstorm struck Kemp and knocked down huge trees creating openings in the forest, dramatically altering its condition. In one area, 30 to 60 percent of the trees were blown down. This disturbance makes growing space for new tree populations to enter the forest and develop a new cohort of young trees.

"Before the storm," explains Tom Steele, superintendent of the Kemp Natural Resources Station, "this area was dark and dense hemlock forest. The forest floor was barren except for needles."

Some of the 250-year-old trees were toppled in the storm opening the canopy. These openings were quickly colonized and are now a jungle of lush growth. Wind disturbance is a natural process in old-growth forest. Since the storm, researchers at UW-Madison have been visiting the site to study the effects of moderate to severe natural disturbances on forests.

Professor Craig Lorimer, of the UW-Madison Department of Forest Ecology and Management and an expert on old-growth in the Midwest, and aided by graduate student at UW-Madison, has been mapping canopy gaps here to determine how naturally disturbed forests differ from those disturbed by humans. This study parallels studies at the Flambeau State Forest, Northern Highland American Legion State Forest and Argonne Experimental Forest in the Chequamegon-Nicolet National Forest. A goal is to develop guidelines that will assist forest managers in restoring old-growth characteristics and managing old faces.

Within each plot at Kemp, they have analyzed vegetation, plot condition and data on how each tree was windthrown – stem breakage or uprooting. They are keeping tabs on species that survive and depend on forest disturbance to create new habitat, Steele says.

The researchers are also taking photos with a special-shaped lens to show how much of the canopy is open and how much sky the trees block out. Using a computer program, researchers are determining how much light reaches the spot where each photo is taken during the growing season. The amount of light reaching the forest floor is important because it affects what plant species will grow there.

Changes in attitudes

David Mladenoff, a professor of Forest Landscape Ecology at the University of Wisconsin-Madison coordinated the original eight-year study on old-growth forests and their management and has written scientific articles about old-growth forest issues.

He became interested in old-growth forests as a Ph.D. student at UW-Madison where he studied the importance of tree falls and gaps to nutrient cycling in the old-growth of the Porcupine Mountains of Michigan.

Much of his work is funded by the Department of Natural Resources.

"What has changed since the 1980s when I was studying old-growth in college is that there is more appreciation now for having forests of all age classes and tree species," Mladenoff says. "People used to consider old-growth merely old and poor producers of wood, fiber or wildlife. But that attitude is changing."

Mladenoff's work consists of measuring gaps in the forest canopy as part of the Flambeau old-growth project, reconstructing pre-settlement forests, measuring the importance of having large coarse woody debris (downed wood) in forests, modeling climate change, and looking at chronic wasting disease and how a dramatic reduction in deer population may change a forest.

"It is exciting to see a growing public appreciation and interest in having a more diverse representation of what was on the landscape historically," Mladenoff says. "And forest managers are seeing that you can maintain these values in ways that are not in conflict with managing for forest products."

Natasha Kassulke is the associate editor of Wisconsin Natural Resources magazine.