Learn about the basics and how to sustain forest resources
The Dickinson Conservation District regularly hosts events to educate the public about forestry and other conservation issues. Please visit our home page to learn more.
What is Forestry? Forestry is an applied science that guides the responsible management of forest resources to meet society's needs and landowners' objectives. Professional Foresters are trained at Universities in a large number of subjects, including dendrology (the study of trees and their identifying characteristics), forest ecology, forest mensuration (tree and land measurements), statistics, natural resource policy, economics, and silviculture. Silviculture is the cornerstone of forestry, and is defined by the Society of American Foresters as "the art and science of controlling the establishment, growth, composition, health, and quality of forests...to meet the diverse needs and values of landowners and society on a sustainable basis" (Society of American Foresters 2015). Forestry as an Art Although forestry is rooted in science, it is also considered an art, because foresters must use creativity and imagination when applying their knowledge to the land.
Michigan's Forests Michigan is heavily forested and ranks 11th in the nation in terms of total forestland. The state contains approximately 20 million acres of forestland, which is approximately 53% of the state's total area. 82% of the forests are found in the Upper Peninsula (45%) and Northern Lower Peninsula (37%).
Forest Types Certain tree species predictably grow together, because they share certain tolerances or intolerances for environmental conditions. For example, tree species that can tolerate very wet soils will likely be found in a swamp. Geology, climate, and historical disturbance ( logging, wildfire, windstorms, insect outbreaks, etc.) are just a few of the complex environmental factors that influence where trees grow on the landscape. Groups of tree species that commonly grow together in a geographical area are called forest types. The mapping of forest types is useful to landowners and forest managers, because it allows them to categorize their resource and provides a basis for decision making. The state of Michigan contains 23 common forests types, and the following links provide information about 10 of the more common ones. These bulletins were written by Bill Cook of Michigan State University Extension.
The figure illustrates the percentage of timberland by forest type. It was recreated from data in Michigan's Forests, 2009.
Forest Ownership People own forests for a variety of reasons. Individuals or families often own forests for personal use and enjoyment, while corporations own forests for financial gain. Foresters collect the information necessary to sustainably manage a forest, but the decision to manage one way or another ultimately resides with the landowner. For example, if a forester identifies a stand with trees that are dying from disease, a corporate owner might harvest all of the diseased trees to salvage financial value and to regenerate a new forest. An individual, on the other hand, might choose to retain some or all of the diseased trees to provide habitat for cavity dwelling birds. Both decisions are valid, because they accomplish landowner objectives.
This figure shows the distribution of Michigan's forests across different ownerships. As you can see, families and individuals own the largest share of the State's forests.
Forest Management A common question posed to foresters is, "Why do humans need to manage forests? Can't nature manage itself?" Additionally, many people believe that humans should "protect" forests by setting them aside and leaving them alone. A brief answer to this question is, humans need forests. Forests provide a large number of ecological services, such as cleaning the air and water, but they also provide a large number of material services. Wood and wood products are used in over 5000 commodities that humans use. Wood has been shown through scientific study to be the most sustainable and environmentally friendly building material currently available. Forests also provide livelihood to many people around the world. In Michigan alone, forests support 154,000 jobs and contribute $14 billion to the state's economy annually. Furthermore, despite Michigan's strong logging sector, our forests produce more than twice as much wood as is harvested by loggers each year.
It is important to understand that using forests and protecting forests go hand in hand. A landscape of managed forests is a landscape of healthy forests. The disturbance caused by well planned timber harvesting promotes the growth of high quality, healthy trees and creates forests that are diverse in both species and in age. Having various ages of forests on the landscape is critically important for wildlife. As an example, half of the migratory birds found in the Midwest use young forests (< 20 years old) habitat. This simple fact dispels the myth that old-growth is the most important forest type. To learn more about the importance of young forests, please visit the Ruffed Grouse Society's webpage.
This photo shows an aspen stand 1 year after harvest. This stand contains thousands of seedlings per acre and provides food and cover for a large number of birds and mammals. If left undisturbed, this aspen forest type will convert to a different forest type. Periodic disturbance, whether it be logging or wildfire, perpetuates aspen in the landscape.
Silviculture As previously mentioned, silviculture is "the art and science of controlling the establishment, growth, composition, health, and quality of forests...to meet the diverse needs and values of landowners and society on a sustainable basis" (Society of American Foresters 2015). Foresters use data gathered from a forest to determine which silvicultural system is appropriate. Silviculture encompasses many non-timber harvesting practices, such as using herbicide to control undesirable vegetation or thinning stands of young trees, but this section will focus on silviculture's role in harvesting trees for commercial use.
Even-aged vs. Uneven-aged Forests Before delving into the major silvicultural systems used in Michigan, it is important to explain the difference between even-aged and uneven-aged forests. If a forest begins growing after a catostophic disturbance, such as a wildfire, tornado, or clearcut, then the majority of the trees in that forest will be similar in age. This is called an even-aged forest. During the timber boom (1880-1920), most of the forests in the U.P. were cutover and burned; and therefore, many of the forests in the U.P. are even-aged. Forests that are periodically disturbed on a smaller scale will likely have trees of different ages growing together. For example, a windstorm topples individual or small groups of trees. This creates gaps in the forest canopy that fill in with young trees. This is called an uneven-aged forest. Some forests that begin as even-aged become uneven-aged overtime.
Silviculture System The silviculture system selected to manage a stand of trees within a forest must satisfy certain goals. The four major silvicutlural goals are:
Provide for natural regeneration of desired forest trees
Provide forest products for the good of the owner and society
Improve the quality of health of the forest
Satisfy the goals and objectives of the forest owner
Forests must be creativity when developing a silvicultural system to satisfy these goals, but a system can generally be placed into 1 of 3 categories. The following explanations for these systems were taken directly from Silvicultural Systems, written by Bill Cook in 2013.
Selection system: Creates uneven-aged forests This is, perhaps, the most commonly applied silvicultural system in Michigan, and is the most commonly misapplied. Individual trees are marked for removal in a commercial harvest. The remaining trees will benefit from the treatment, increasing the overall quality of the stand. The increase in light to the forest floor will encourage tree regeneration. Two common variations of the selection system exist; single tree selection and group selection.
Marked trees may be distributed evenly throughout the stand resulting in a uniform density of trees. This is the more classic version of the selection system. Single tree selection tends to create an ecological environment that favors sugar maple, or other shade tolerant species, and enhance the quality of sawtimber. Good quality sugar maple sawtimber typically garners the highest monetary value of all Michigan species.
Group selection removes both single trees and groups of trees, resulting in a more variable stand density. The gaps created by harvesting groups of trees encourage greater tree species diversity. Gaps are often created around or next to certain tree species, such as white pine, hemlock, or yellow birch, to favor regeneration of those species. Group selection resembles natural disturbance of these forest types.
A variant of the selection system is called "crop tree selection" in which harvest is designed to maximize growth on preferred trees within a stand. It is often applied to even-aged pole-size stands in which all trees are approximately the same size. Certain "crop trees" are identified, based on their species, quality and spacing. Important crown competitors are removed to provide growing space for the designated crop trees.
Selecting trees for removal generally follows a priority list:
High risk trees
Highly defective trees
Trees with poor form
Priorities might vary with the particular stand and specific desired outcomes. The eventual outcome produces an all-aged or multi-aged stand structure of increasing quality and health.
While the selection system will achieve marvelous results under the right circumstances, forest owners should be aware of similar practices incorrectly called "selective" cutting. The practice of "high-grading" is the removal of the high monetary value trees and leaving the rest without regard for future stand conditions. This is generally regarded as poor forestry because repeated applications inevitably lead to poor-quality stands. Another example is diameter-limit cutting, in which all trees above a certain diameter are cut. This is another form of high-grading that also leads to poor quality stands. Partial cutting is sometimes done in inappropriate forest types, such as aspen, where it leads to degradation of stand quality and results in poor regeneration. Selection system silviculture requires the greatest amount of knowledge and experience. Working with a consulting forester is highly recommended.
A northern hardwood stand in the western U.P. marked by a forester for a single tree selection harvest.
Shelterwood system: Creates even-aged forests This even-aged system involves the harvest of all mature trees in a two or three stage process over several years. Additionally, some stands might be commercially thinned one or more times before they reach maturity. If regeneration is not present, then a portion of canopy trees are harvested to increase the amount of light to the forest floor and encourage regeneration. A ground treatment might be required to expose mineral soil or remove undesirable competing vegetation. The next cut, or first cut if regeneration is already present, removes most of the overstory and provides light to increase the growth rates on understory regeneration. Partial shade modifies the micro-environment to avoid excessive heat and dry conditions. Remaining mature trees are those that are windfirm and of good quality that will rapidly increase in size and monetary value. When the next generation of trees reaches an appropriate size, maybe 6-8 feet high, then the residual overstory is removed. In Michigan, shelterwood silviculture is most often applied to oak stands but can be applicable to other forest types as well.
Clearcut system: Creates even-aged forests Clearcutting is the complete, or nearly complete, removal of a mature stand and is a legitimate system when appropriately applied. Forest types that require full sunlight and warm soil temperatures for regeneration and subsequent growth require this sort of disturbance. In nature, catastrophic events such as wildfire and windstorm provide the necessary ecological regeneration conditions. Classic example forest types are aspen and jack pine.
Seed-tree silviculture is a variation of clearcutting. A small number of trees can be left on-site to provide a seed source. This is sometimes done with white pine, red pine, or oak. Leaving a few trees may also provide benefits for visual quality and certain species of wildlife (such as raptor roosts and snags for cavity nesters). Residual trees must be windfirm and have the ability to adjust to rapidly increased exposure to the sun.
Silvicultural clearcutting (as opposed to other clearcutting) harvests trees at the right time, before over-maturity, to guarantee the optimum amount of vigorous regeneration. The new stand is even-aged and requires few additional practices until the next harvest. The key to the appropriate application of clearcutting is the timing in order to produce the next forest stand.
A stand in the western U.P. clearcut to regenerate aspen