A controlled burn, also called a prescribed burn (Rx burn), is a method used to intentionally start a fire to change the types of plants and decaying material in an area. The goal may be to manage forests, help ecosystems recover, clear land, or reduce the risk of large wildfires. Controlled burns are sometimes called hazard reduction burning, backfire, swailing, or a burn-off.
Controlled burns are often done during cooler months to remove fuel that could cause more dangerous fires. These burns can help some tree seeds grow by exposing soil minerals that improve seedling health. In grasslands, controlled burns encourage the growth of native grass species. Some seeds, like those from lodgepole pine, sequoia trees, and chaparral shrubs, are pyriscent, meaning fire heat causes their cones or husks to open and release seeds.
Fire is a natural part of forest and grassland ecosystems. For many years, indigenous people around the world used controlled burns to support plant and animal life and grow wild crops, such as fire-stick farming practiced by Aboriginal Australians. In North America and Australia, colonial laws forced indigenous people to leave lands they had managed with fire and stopped them from using traditional controlled burns. As wildfires became more frequent and severe in the 20th century, land managers began using controlled burns again and working with indigenous leaders to care for the land.
Uses
Controlled burning helps reduce fuels, improves wildlife habitats, controls competing plants, helps manage tree diseases and pests, and supports species that depend on fire. Scientists study how different fire characteristics, such as how often fires happen, how hot they are, how severe they are, how spread out the burned areas are, the size of the area affected, and the time of year when fires occur, can help achieve conservation goals. These studies may look at how fires in the past naturally happened and how to copy those patterns today.
Controlled fire can be used to prepare areas for planting when machines cannot reach because of rough terrain. After fuel treatments, some plants may grow more quickly in a few years because the soil gets more nutrients and there is more sunlight and space.
Many trees rely on fire to remove other plants and release their seeds. For example, giant sequoias and other fire-adapted trees depend on fire to reproduce. Their cones are heat-sensitive and only open after reaching a certain temperature. This helps giant sequoia seedlings grow because fire removes other plants that compete for resources. These trees benefit from moderate fires in older forests, but climate change is causing more frequent and intense fires in North America. Controlled burns can help manage fire cycles and reduce the risk of dangerous fires in forests with fire-adapted species, such as in Canada’s boreal forests.
Eucalyptus regnans, or mountain ash in Australia, has evolved to survive fires. When fires happen, these trees quickly replace damaged parts and release seeds stored in capsules. During wildfires, these capsules drop most of their seeds, and while the adult trees are destroyed, many seeds survive by using nutrients from the ash. These trees grow quickly and form new forests of the same age. Other trees, like poplars, can regrow after fires because their underground root systems are protected from fire.
In North America and Australia, native grasses are adapted to survive occasional low-intensity fires. Controlled burns in prairie areas mimic these fires, helping native plants grow while reducing non-native plants. These burns are done in early spring before plants start growing, when the soil is wetter and there is less fuel on the ground to keep the fire low-intensity.
Controlled burns reduce the amount of plants on the forest floor. This can lower the intensity of wildfires or stop them from spreading. Burning before wildfire season can protect homes, buildings, and reduce risks from dead trees, such as those left after pest infestations.
In some parts of the world, controlled burns are used in farming and are called "slash and burn." In more developed countries, this is part of a farming method called shifting cultivation. This technique clears land by burning crop remains and killing weeds. It is cheaper than using chemicals or plowing, but it produces smoke and pollution, which makes it less popular near homes.
Controlled fires are often used to manage the growth of woody plants in grasslands and shrublands, helping balance the number of trees and grasses.
In Northern India, especially in Punjab, Haryana, and Uttar Pradesh, uncontrolled burning of agricultural waste causes serious air quality problems in those areas and nearby regions.
In East Africa, bird numbers increased months after controlled burns were done.
In Australian savannas, controlled burns can reduce long-term greenhouse gas emissions. An example is the West Arnhem Fire Management Agreement, which uses controlled burns in Western Arnhem Land to reduce the impact of fires that would otherwise happen later in the dry season. This method, called "patch burning," creates a mix of burned and unburned areas, which helps reduce the size and intensity of large fires.
Procedure
Health and safety, protecting people, stopping fire from spreading, and reducing smoke effects are the most important factors when planning a controlled burn. The main reason for fuel treatment is to prevent loss of human lives and buildings. However, other factors can be adjusted to support biodiversity and change the age of a group of trees or the mix of plant species.
To reduce smoke effects, burning should happen during daylight hours when possible. In temperate climates, burning grasslands and prairies before native plants start growing for the season helps protect them, as non-native plants grow earlier in spring and are more likely to be affected by fire.
Back burning, also called a back fire, is a method where vegetation is lit so it burns against the wind. This creates a slower, easier-to-control fire. Controlled burns use back burning during planned events to form a "black line," a barrier where fire cannot spread. Back burning is also used to stop wildfires already happening. Firebreaks, such as rivers, roads, or cleared areas, serve as starting points for lines of fire.
Head fires, which burn with the wind, are used between two firebreaks because they spread faster and burn more intensely than back fires. Head fires are chosen when back fires move too slowly, either because the fuel is very moist or the wind is weak. To speed up back fires, flank fires can be used. These fires are lit at right angles to the wind and spread in the same direction.
In Ontario, Canada, controlled burns are managed by the Ministry of Natural Resources. Only trained personnel can plan and start controlled burns within the province or when the Ministry is involved. The team conducting the burn includes roles such as Burn Boss, Communications, Suppression, and Ignition. Planning begins with submitting an application to a local fire office. After approval, a burn plan must be submitted weeks before the event.
On the day of the burn, team members meet with the Burn Boss to discuss strategies for starting and controlling the fire, health and safety rules, fuel moisture levels, and weather conditions. Local fire authorities are informed by phone, while others prepare drip torches with fuel, fill suppression packs with water, and set up barriers to keep people away. Drip torches are canisters with fuel and a wick used to start fire lines. Safe zones are established where fire cannot cross due to natural or human-made barriers like water or tilled soil.
During ignition, the Burn Boss shares details about the fire’s progress with the Communications Officer, who records this information. The Communications Officer also reports wind speed and direction, helping the Burn Boss adjust fire lines and smoke direction. After ignition in a section, the suppression team uses tools to extinguish remaining smoldering material. Equipment like RTVs with water tanks and hoses is used for suppression. Once all smoldering is controlled, the Burn Boss ends the burn and informs local fire authorities.
Slash from forestry work is burned using different methods. Broadcast burning spreads slash over a wide area, while pile burning gathers it into piles, sometimes called bonfires. High temperatures from pile burning can damage soil physically, chemically, or make it sterile. Broadcast burning uses lower temperatures and causes less soil damage, though soil treatment after burning may still be needed. In lop and scatter burning, slash is left to compact naturally or with machinery, creating a lower-intensity fire if not packed too tightly.
Reducing ground fuels before they form a path for fire to spread upward can lower the risk of deadly fires. Studies show that thinning forests reduces fire intensity and flame length compared to untouched or fire-proofed areas.
Aerial ignition is a controlled burn method where fire-starting devices are dropped from aircraft.
History
Wildfires have two main causes: natural events, such as lightning, and human actions. Controlled burns, which are intentional fires used to manage land, have been practiced for a long time. Humans have used fire to clear land since ancient times. Studies show that before European colonization, indigenous groups in North America and Australia regularly used fire to manage forests and grasslands. These fires helped release nutrients for plants, reduced competition for crops, and removed flammable materials that could cause large, dangerous fires.
In the early 20th century, U.S. federal policies aimed to stop all fires. However, since 1995, the U.S. Forest Service has gradually reintroduced controlled burns into its management plans. Fire suppression, or stopping fires from spreading, has changed ecosystems in North America. Habitats that depend on fire, like oak savannas, are now endangered. In the Eastern U.S., trees that are sensitive to fire, such as red maples, are increasing, while fire-resistant species like oaks are declining.
For the Anishinaabeg Nation near the Great Lakes, fire is seen as a living force that transforms landscapes through destruction and regrowth. People are responsible for caring for the land and its ecosystems. Fire helps reveal hidden plant seeds and has been used to manage land. Before colonization, fire was common in Ontario, but colonial laws limited indigenous practices. Later, fires caused by railroads and agriculture were used to clear land, which was seen as taming the wilderness for cities. A conservation movement led by Edmund Zavitz in Ontario later banned all fires, both natural and intentional.
In the 1970s, Parks Canada started small controlled burns, but wildfires still outpace the area intentionally burned. In the late 1980s, Ontario’s Ministry of Natural Resources began using prescribed burns, leading to formal programs and training. In British Columbia, restrictions on controlled burns increased wildfire intensity. After a severe wildfire season in 2017, Indigenous leaders and officials recommended returning to traditional prescribed burns. The provincial government agreed to use controlled burns as a management tool.
In Oregon, farmers needed permits to burn fields starting in 1981. Rules became stricter in 1988 after a deadly car crash caused by smoke from field burning near Albany. This led to more oversight and proposals to ban field burning. Controlled burns can sometimes get out of control, as seen in the 2020 Calf Canyon/Hermits Peak Fire in New Mexico, which began from two separate controlled burns managed by the U.S. Forest Service.
The U.S. policy on controlled burns has evolved over time. After colonization, fire suppression laws were used to stop Indigenous practices, despite scientific support for prescribed burns. This harmed ecosystems to benefit logging industries. By the 1970s, the National Park Service began authorizing controlled burns. The 1988 Yellowstone fires increased public debate about fire management. Media coverage exaggerated the fires’ impact, leading politicians to prioritize fire suppression over protecting natural areas.
Today, policymakers still debate wildfire management. Senators in Oregon and Idaho have pushed to reduce funding for fire suppression after severe fires in 2017. Climate change has worsened drought conditions, leading to more wildfires. Since 1988, many states, including California, have improved controlled burn programs by training more personnel and making it easier for landowners to use them.
In the European Union, farmers burn crop stubble after harvest for plant health, but this is regulated. In northern Great Britain, a practice called muirburn is used to manage grouse moors, creating habitats for red grouse. However, burning peatlands releases carbon and harms ecosystems, despite government restrictions.
The Maasai people in Africa use traditional burning in savannas before the rainy season to create grazing land and prevent large fires. However, this practice has decreased due to unpredictable rainfall, accidental fires, and government policies. Indigenous Australians have long used controlled burns, like cool burning, but these practices were suppressed during colonization. Recent land rights returns and policy changes have increased prescribed burning in Australia.