Prescribed Burn
Prescribed Burn
Prescribed burning in forestry
Prescribed burning in vegetation management
Prescribed burning in habitat management
Prescribed burns (sometimes also called controlled burns or prescribed fires) involve the controlled burning of vegetation by fires to achieve some desired management effect. They can be used to encourage a desired type of forest regeneration, to prevent the
invasion of prairies by shrubs and trees, to decrease the abundance of pathogens, to prevent catastrophic wildfires by reducing the accumulation of fuel, or to create or maintain habitat for certain species of animals. Prescribed burns can be very useful tools in vegetation and habitat management, but it is critical that this practice be based on a sound understanding of the ecological effects the result.
Prescribed burning in forestry
Prescribed burns are an important tool in some types of management systems in forestry. Most commonly, fire is utilized to reduce the amount of logging debris present after clear-cutting. This practice is generally undertaken to make the site more accessible to tree planters. The use of prescribed burning for this purpose means that the site does not have to be prepared using more expensive physical techniques such as scarification by heavy machinery.
Sometimes prescribed fire is also useful in developing better seedbeds for planting tree seedlings. Prescribed burns can also be used to encourage natural regeneration by particular types of trees that are economically desirable such as certain species of pines. When using fire for this purpose, it is important to plan for the survival of an adequate number of mature seed trees. If this is not accomplished, the burned site would have to be planted with seedlings grown in a greenhouse.
Prescribed burning makes available a flush of certain nutrients in ash, particularly, calcium, magnesium, potassium, and phosphorus. However, there may be little biomass of regenerating vegetation on the site immediately after a burn, and therefore there is little biological capability to take up soluble forms of nutrients. Hence, much of the nutrient content of the ash may be lost from the site during heavy rains. In addition, most of the organic nitrogen of the logging debris becomes oxidized during combustion to gaseous compounds such as nitric oxide, and the fixed nitrogen is therefore lost from the ecosystem.
The use of prescribed fire in forestry is most suitable for forest types that are naturally adapted to regeneration after wildfire, for example, most pine and boreal forests. The use of this industrial practice in other types of forests, particularly temperate rain forests, is more controversial.
Prescribed burning in vegetation management
Many natural ecosystems are maintained by wildfires. In the absence of this sort of disturbance, these ecosystems would gradually transform into another type through the process of succession. For example, most of the original tall-grass prairie of North America occurred in a climatic regime that was capable of supporting shrubs or oak-dominated forests. However, the extensive transformation of the prairie into these ecosystems was prevented by frequent ground fires that were lethal to woody plants but could be survived by most of the herbaceous species of the prairie. Today, tall-grass prairie has been almost entirely converted into agricultural usages, and this is one of North America’s most endangered types of natural ecosystem. The few remnants of tall-grass prairie that have been protected are managed using prescribed burns to prevent the incursions of shrubs that would otherwise degrade the integrity of this ecosystem.
Tall-grass prairies are maintained by relatively frequent fires. However, some types of forests may need fires on a much longer rotation to prevent their conversion into another type of forest community. For example, forests in California dominated by redwoods (Sequoia sempervirens) need occasional fires in order to reduce the abundance of more tolerant species of trees and thereby prevent these from eventually dominating the community. Fire is also useful in the redwood ecosystem in preventing an excessive buildup of fuels that could eventually allow a devastating crown fire to occur that would kill the mature redwood trees. In some cases, prescribed burning is used to satisfy the requirement of redwood forests for low-intensity fires.
Prescribed burns can also be used to prevent catastrophic wildfires in some other types of forests. In this usage, relatively light surface fires that do not scorch the tree canopy are used to reduce the biomass of living and dead ground vegetation and shrubs and thereby reduce the amount of fuel in the forest. When this practice is carried out in some types of pine forests, there is an additional benefit through enhancement of natural regeneration of the pine species which require a mineral seedbed with little competition from other species of plants.
Prescribed burning in habitat management
Prescribed fire has long been utilized to manage the habitat of certain species of animals. In North America, for example, the aboriginal nations that lived in the Great Plains often set prairie fires to improve the habitat for the large animals that they hunted as food. This was especially important to people living in regions of tall-grass prairie, which could otherwise revert to shrub- and tree-dominated ecosystems that were less suitable for their most important hunted animals such as buffalo (Bison bison).
Prescribed fires have also been used to enhance the habitat of some endangered species. For example, this practice is utilized in Michigan to develop stands of jack pine (Pinus banksiana) required as habitat by the endangered Kirtland’s warbler Dendroica kirtlandii). This bird does best in even-aged stands of jack pine aged seven to 25 years old and about 6.6 to 19.7 ft (2 to 6 m) tall. Wildlife managers ensure a continuous availability of this kind of habitat by planting stands of jack pine and by deliberately burning older stands.
Prescribed burns have been favored as a way to improve grazing of animals, improve human accessibility, control competing vegetation, help fire dependent species, and control diseases and pests. Opponents of prescribed burns state that it is a detriment to the environment and may harm some desired species of plants and trees.
KEY TERMS
Prescribed burn— The controlled burning of vegetation as a management practice to achieve some ecological benefit.
Resources
BOOKS
Babe, Robert E. Culture of Ecology: Reconciling Economics and Environment. Toronto, Canada: University of Toronto Press, 2006.
Kruger, Linda, E. Understanding Community-Forest Relations. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Service, 2003.
Tietenberg, Thomas, H. Environmental and Natural Resource Economics. Boston, MA: Pearson/Addison Wesley, 2006.
Bill Freedman