Northern hardwood forests are Michigan's most complicated, common and valuable forest type. Many variables dictate the type of management necessary to achieve a set of objectives.
Foresters use the term northern hardwoods to describe a particular forest type. However, northern hardwoods are not simply hardwood trees that grow in the north. It is a poor term and confusing for almost everyone else.
Northern hardwoods are forests dominated by sugar maple. The classic northern hardwood co-components are beech, basswood and yellow birch. According to the Michigan forest inventory data, the most common associates are actually red maple, hemlock, basswood and yellow birch. Common secondary species include beech, black cherry, quaking aspen and white ash. The mix depends where you are in Michigan, among other factors.
Northern hardwoods is the most common forest type in Michigan, making up a quarter of all Michigan forest area and nearly a third of the volume. Sugar maple alone makes up 15 percent of the state’s forest volume and is the most common species. Arguably, it also is the most valuable in terms of dollars and, perhaps, in visual quality.
In the 1920s, researchers began to study Lake States’ northern hardwood stands to better understand how they grow and how to produce more high quality logs. In 1957, Carl Arbogast published a benchmark paper outlining marking guides for the selection management system in northern hardwoods. Other publications subsequently refined the management system, such as Carl Tubbs’ Manager’s Handbook in 1977.
The classic “selection management” system for northern hardwoods has been quite successful in producing high quality timber. It is possibly the most commonly-employed forest management system in Michigan. However, there are aspects of this management that warrant further thought.
Not all forest owners desire high-quality timber as a primary management goal. This single-tree selection system pushes forests toward high levels of sugar maple, and this “maple-ization” may lead to lower species diversity. Forests of lower diversity are less resistant to native pests and may be less resistant to exotic pests and changes in climate.
Diameter class structure, as described by Arbogast and Tubbs, may not be the same as variable ages. Northern hardwood stands may have multiple diameter categories but most of them are often the same age. A truly “all-aged” stand will increase diversity, promote forest health and better resemble natural forest conditions.
Most of our northern hardwood stands are even-aged second- or third-growth forests with few large fallen trees and few standing “snag” trees that are important for cavity-nesting wildlife and other flora and fauna. Classic single-tree selection discriminates against these sorts of ecological features.
Forest researchers and practitioners have long recognized the value of cutting pockets or gaps into northern hardwood forests to encourage species that are more sun-loving than sugar maple. This “group selection” practice more closely resembles natural wind disturbances than single tree selection, and might diversify a northern hardwood stand.
Gaps range from 35 to 80 feet. Placement is often around or next to desired tree species, such as white pine, hemlock or yellow birch. Sometimes, a thinned-canopy or shelterwood-like treatment may be employed in gaps of one to several acres.
Even-aged management of northern hardwoods (aka versions of clearcutting) is also appropriate in some circumstances, especially when advance regeneration is present or soils are limiting. Many northern hardwood stands have little regeneration or poor quality regeneration. One key concern with any management system is how well the forest will regenerate. Regeneration response to treatments is highly variable, depending upon stand characteristics, soil types, presence of Pennsylvania sedge, pressure from deer browsing and other factors. There is not a one-size-fits-all system that works every time in every stand. Nature is not quite that uniform. This is one more good reason to hire the expertise of a consulting forester from Michigan State University Extension.
In addition to managing for quality timber, species diversity, stand resilience, forest health and regeneration, there are the habitat effects on wildlife. Northern hardwood stands are not the best habitat for popular game species such as deer, grouse and turkey. However, there are many other interesting species that attract the attention of many forest owners. Northern hardwoods host a wide variety of songbirds, small mammals and amphibians. Shaking-out a cluster of flying squirrels from a hollow tree is a memorable experience. Goshawks, warblers and ovenbirds enhance the character of the forest in the summer. Finding a red-backed salamander under an old rotting log is a curiosity for most forest owners. A bear den is nice to have but it’s important to maintain your distance.
On top of that there is the myriad species of shrubs, wildflowers, ferns, bryophytes and fungi.
Unusual forest practices to enhance non-game wildlife include girdling large, old trees to create snags sooner than what nature might provide. Preferably, these are trees with low monetary value. Dropping and leaving large trees creates a microhabitat for an entire suite of species.
A few of these trees per acre would be plenty. An entire forest would be overkill, unsightly, and won’t really increase wildlife population numbers. Many species tend to be territorial.
Protecting those temporary shallow pools of springtime water (vernal ponds) will help produce another group of species. These wet habitats can be valuable habitat, and sometimes uncommon, in most northern hardwood stands.
Northern hardwood management is complex, perhaps the most challenging of all our Lake States forest types. Find a forester. Learn about it. Make some money. Have some fun.