Silviculture

Summary

Silviculture is a branch of forestry. The term is based on silva, the Latin root for "woodland." Silviculturists are concerned with the protection, restoration, and management of forest resources, often for timber production but also for wildlife habitats, recreation, and other uses. Silviculturists are involved in harvesting the forest for its timber value or to reduce wildfire risk and in reestablishing the forest in ways that ensure that it is sustainable. Controlling tree growth, managing the composition of tree stands, protecting trees from pathogens, and ensuring the quality of trees are some of the activities that make up the field of silviculture.

Definition and Basic Principles

Silviculture is the art and science of establishing and caring for forests to meet the needs and management objectives of landowners and society. Although timber production sustainability is often the most important objective of silviculture, other benefits of a well-managed forest are preservation of wildlife habitats, water conservation, and aesthetics. Silviculture relies on ecology and natural processes, including fire, to control forest composition and growth. However, too much interference in the forests by silviculturists can negatively affect the forest ecosystem.

Silviculture is practiced during all stages of the life of a tree stand to meet the dual goals of sustaining forest growth and satisfying market demands and landowner objectives. A silviculturist's forest management decisions concern not only the present forest and timber crop but also future forest quality and growth. Silviculturists use many methods, such as selectively cutting trees while retaining some of the high-grade tree growth for the future. Other practices include cutting of all trees except the ones with the best genetics for producing seeds to regenerate the forest and cutting out all undesirable trees in a stand to allow for natural regeneration of a desirable species whenever possible. In both cases, the harvesting methods allow for better growth because the new trees are in full sunlight rather than being blocked by the overstory.

Background and History

Society has been removing trees to satisfy its needs since ancient times. Many early settlers thought little about the value of the forests and clearcut them to allow for agriculture, development, and wood production with little thought of the future, as the supply of trees appeared to be limitless. The practice of silviculture, however, became a necessity in Europe by the 1600s to restore the timber used in everyday life for fuel and building materials. The production of timber also became important to the economy of many societies in the eighteenth to twentieth centuries, and silviculture came to concentrate on ensuring that there would be future growth available for harvesting.

Early silviculture involved practical experience, but during the 1700s, Henri-Louis Duhamel du Monceau, a French botanist, was instrumental in applying scientific methods to forest regeneration, including experimenting with plant physiology. In the mid-1800s, Martin Faustmann, a German forester, published the Faustmann formula for capital evaluation, which became the basis for modern forest valuation. By the end of the 1800s, silviculturists had developed a theory of tolerance, and forest experimental stations had been established to gain a better understanding of the relationship between forests, organisms within the forest, and soil conditions. In the twenty-first century, agencies such as the US Forest Service (USFS) are concerned not only with timber production and harvesting but also ecology and environmental sustainability.

How It Works

The practice of silviculture is systematic and involves many different operations, including preparing the site, cultivating, regenerating, thinning, harvesting, clearcutting, pruning, fertilizing, and prescribed burning. Before any silviculture applications are implemented, however, silviculturists must conduct surveys of the forest to develop silviculture plans that specify not only the goals and objectives of silviculture activities but also the means of achieving them. These plans are known as silvicultural prescriptions. Often, global positioning systems (GPSs) and geographic information systems (GIS) mapping are used, and survey data are entered into databases for analysis of forest resources, such as wildlife habitats and watersheds. Two types of plans that a silviculturist might develop include regeneration and thinning plans.

Regeneration Plans. Trees are lost through harvesting, wind, fire, insects, and disease. Silviculture activities include implementing methods for regenerating tree stands. Among the methods are tree seeding, coppice, clearcutting, shelterwood, selection cutting, and variable retention. When trees are grown from seed, the seeds are collected from parent trees in the forest that are located close to the planting site. Before planting takes place, data are analyzed to ensure that the biophysical environment of the planting site will allow the tree seedlings to survive. Coppice techniques, in which trees are cut and then regenerated from sprouts and suckers, can result in even-aged tree stands, although the initial cutting can reserve some of the original trees to develop a two-aged stand. Clearcutting is used to generate new, even-aged, or two-aged forest stands either through natural seeding or replanting methods. Shelterwood regeneration results in new, even-aged stands, as silviculturists reserve mature trees and then manage new tree growth that develops in the undergrowth and is sheltered by the reserve trees. Selection cutting involves the removal of older trees, which enhances the growth and health of the remaining trees, while variable retention involves retaining of some trees in a harvested stand until the stand undergoes the next harvest in order to maintain specific tree species on a site.

Thinning Plans. Trees that are planted too close together are deprived of sun, water, and nutrients needed for growth. Therefore, a silviculturist must engage in planning for tree thinning to allow for sustainable growth. Thinning provides for tree stands that are more resistant to fire, wind, pests, and disease. Thinning techniques may serve commercial as well as noncommercial purposes and include crown, low, free, and selective thinning. In crown thinning, dominant trees are removed from a tree stand to encourage growth of codominant trees that may be more desirable. When employing the low thinning method, the silviculturist removes dominant trees from the understory to enhance growth in the overstory. Free and selective thinning techniques allow the silviculturist to remove less desirable trees in the understory or overstory, often to establish an even-aged tree stand made up of one species. Once the thinning is completed, however, a regeneration plan must be implemented.

Other Silviculture Practices. Before regeneration of a harvested site can take place, the planting site must be prepared through activities such as prescribed burning and trenching. A planted forest that consists of genetically enhanced seedlings will regenerate faster than a naturally seeded forest, and a planted forest will also receive more care by the silviculturist, including removal of naturally occurring competing plants, application of pesticides to combat insects and diseases, and fertilization to enhance growth. Many of these methods are intended to promote sustainable forestry.

Applications and Products

Silviculture involves maximizing multiple uses of the forest by private and public landowners in a manner that preserves and sustains the forest resources for the future. Silviculture is based on the natural science of silvics, which concerns the study of environmental factors, such as soil conditions, climate, competing plants, and other living organisms, and how they affect the vegetative biomass. From this study, the silviculturist applies scientific methods to ensure adequate growth of the trees used in multiple applications and products.

Timber Forest Products. Forests provide many marketable wood products, from lumber used in building and construction industries to timber that is made into wooden panels, barrels, and gift items. Commercial harvesting also supplies the timber needed by the pulp and paper industry. Often a silviculturist is involved in growing a specific species of tree because of its marketability, such as for furniture production. Silviculturists achieve this objective by using herbicides to control competing species and planting high-quality seedlings of the plant variety that is desired.

Nontimber Forest Products. Forests are managed through silviculture to produce more than timber. Examples include maple products, nutmeats, and shell products that have economic viability through the silviculture practice of single-species planting. Silviculturists also manage undergrowth vegetation in forests to produce products such as edible ferns and mushrooms. Trees produce important oils, including the cedar oil used in many cedar-based products such as insecticides. Timber branches and leaves are used in wreaths and garlands, dried and sold for decorating products, or woven together into baskets and screens.

Wood Energy. Forests are also harvested as a biomass for energy, including the production of firewood and charcoal. Silviculture practices for this application usually involve management for hardwood species through thinning, quality stand rehabilitation, and effective harvesting to mitigate the environmental effects of harvesting on soils, organic matter, and wildlife habitats. The growing market in wood energy production has resulted in the growth of the silviculture contracting industry.

Christmas Trees.Christmas trees are an important seasonal crop for both retail and wholesale economies. Silviculture is practiced by cultivating one species of tree, such as balsam fir. Single species are maintained through weeding of competitive species and shearing, fertilizing, and treating the Christmas trees with insecticides until they are harvested.

Restoration Ecology. Silviculturists accelerate recovery of ecosystems in areas that have been disturbed or destroyed by natural disasters or human beings. They ensure a sustainable and productive forest through reforestation methods and restore and expand wildlife habitats, even creating corridors that link existing and newly expanded habitats by planting the plant species that support specific animal habitats. Restoration ecology also involves the use of erosion control methods that are necessary after floods, fires, and human disturbances, such as mining, to ensure adequate soil for plant growth. These methods include planting fast-growing species that hold the soils in place.

Hydrology and Watershed Protection. Silvicultural activities, such as timber harvesting, can greatly affect watersheds, stream flow, and the underlying hydrology by causing pollution and disrupting existing hydrologic processes. The pollution is often caused by soil erosion created by logging and associated activities, such as road building, and is not easy to control, as it usually does not come from a single source. Because entire watersheds can be negatively affected by poorly managed timbering operations, state and federal laws have been adopted to ensure that silviculturists engage in timber harvest planning before cutting down trees.

Climate Control.Deforestation can affect climate, as trees soak up fossil fuel emissions. Therefore, silviculturists must understand how their activities affect climatic changes and, ultimately, the economies in many countries. Silviculture is being employed as a climate mitigation method by increasing the size of silviculture plantations, especially in areas where drought has become a serious problem. However, expanding the size of plantations to control climate is not always possible because of the need to develop land to meet growing global social needs.

Control of Invasive Plants. Throughout history, non-native plants have been introduced intentionally or by accident for purposes such as food, medicine, and aesthetics, sometimes with negative results, such as lost revenues. Once introduced, about one out of every ten of these non-native plants becomes difficult to control and can destroy ecosystems and habitats. Some of the ways that silviculture methods can be used to overcome these negative outcomes is to plant sterile hybrids of the invasive species and to reintroduce native species into an area.

Pest and Disease Control. Silviculturists act as plant doctors throughout the globe when they apply methods to protect plants from insect and disease hazards. Because insecticides may have side effects and do not remove the cause of the insect invasion, silviculturists use methods such as altering forest conditions, preventing injuries to trees, selective cutting to remove physiologically weakened trees, and accelerating regeneration in areas where there has been an outbreak of insect pests or diseases. When establishing a new tree stand, a silviculturist will introduce tree species that have been able to grow in the area before without devastation from pests and diseases.

Urban Forestry. Silviculture activities can be found around cities. Urban forestry is a type of silviculture that involves planning, cultivating, and maintaining trees and greenspaces in developed communities. Urban forestry can help meet many objectives, including improving public health and enhancing environmental education in urban settings.

Careers and Course Work

Basic coursework for a career in silviculture includes botany, biology, ecology, and forestry. Silviculture is a multidisciplinary field, and students must take courses in multiple fields. Students can concentrate their studies in specific areas, including botany, genetics, and zoology for those interested in stand development, plant composition, habitat management, and ecology. Soil engineering, geology, and hydrology are necessary if site preparation, forest growth, and water quality protection are of interest. Plant physiology, microbiology, and entomology courses are necessary if a student wants to work with insect pests and diseases. Finally, for students interested in timber production businesses, economics, statistics, sociology, planning, and business administration courses will be helpful.

Entry-level positions for silviculture workers do not usually require a college degree. These positions include tree planting, harvesting, stand thinning, and fire control laborers. Those involved in more complex silviculture practices—technicians, regeneration planners, surveyors, genetically enhanced plant producers, forest and ecosystem managers, and applicators of chemical herbicides and fertilizers—require training, certification, and usually college degrees. Many silviculturists hold master's degrees or doctorates, especially those involved in research and certified and licensed silviculturists who prepare silviculture prescriptions. The US Forest Service offers a nine-week graduate-level certification program called the National Advanced Silviculture Program (NASP).

Jobs are available with private timber companies and at all levels of government. Some silviculturists find work as consultants to private landowners. The future is bright for silviculture because of the many demands placed on the forests, their multiple uses, and the wood products they produce.

Social Context and Future Prospects

The growing demand for multiple-use forests and harvesting trees for wood products conflicts with the importance of preserving diverse forest ecosystems. Forests are complex, and silviculturists recognize that by using scientific methods of tree removal and management, forests can adapt to natural changes and those caused by humans. Advancements in technology allow silviculturists to use best management practices to harvest, regenerate, and tend forests to ensure their sustainability. These methods include advance regeneration before harvesting trees, maintaining soil quality and stability before and after tree harvest, genetically improving planting stock, improving the use of chemical fertilizers and herbicides, and protecting water quality by preventing the loss of nitrogen into streams and water bodies through the use of plant buffers.

Silviculturists must educate the public about the many facets of silviculture to destroy the myth that it simply promotes timber production. In the future, silviculture will continue to be useful to people for purposes such as reducing fire risks in areas where residential development coexists with forests and abating specific types of insect pestilence. Silviculturists can also manipulate the landscape to restore former plant communities or establish new plant materials that provide benefits such as habitats for endangered or threatened wildlife species. However, silviculturists must work with members of other disciplines throughout the world, including economists and social scientists, to ensure that the future needs and objectives related to silviculture are met and that private landowners and the timber industries are constantly receiving education concerning the benefits of silviculture in managing forests.

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Gonçalves, Ana C. Silviculture. IntechOpen, 2021. 

Latham, Robert P. Forensic Forestry: A Guidebook for Foresters on the Witness Stand. CRC Press, 2022.

Puettmann, Klaus, Christian Messier, and K. David Coates. A Critique of Silviculture: Managing for Complexity. Island Press, 2008.

"Silviculture." Global Forest Atlas, Yale School of the Environment, Internet Archive, web.archive.org/web/20210123042018/https://globalforestatlas.yale.edu/forest-use-logging/silviculture. Accessed 25 June 2024.

"Silviculture." US Forest Service, USDA, www.fs.usda.gov/forestmanagement/vegetation-management/silviculture/index.shtml. Accessed 25 June 2024.

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