A controlled or prescribed burn (RX), also known as hazard reduction burning, backfire, swailing, back-burning, or a burn-off, is a fire set intentionally for purposes of forest management, fire suppression, farming, prairie restoration or greenhouse gas abatement. A controlled burn may also refer to the intentional burning of slash and fuels through burn piles. Fire is a natural part of both forest and grassland ecology and controlled fire can be a tool for foresters.
Hazard reduction or controlled burning is conducted during the cooler months to reduce fuel buildup and decrease the likelihood of serious hotter fires. Controlled burning stimulates the germination of some desirable forest trees, and reveals soil mineral layers which increases seedling vitality, thus renewing the forest. Some cones, such as those of lodgepole pine, sequoia and many chaparral shrubs are pyriscent, meaning heat from fire opens cones to disperse seeds.
In industrialized countries, controlled burning is usually overseen by fire control authorities for regulations and permits.
There are two basic causes of wildfires. One is natural, mainly through lightning, and the other is human activity. Controlled burns have a long history in wildland management. Pre-agricultural societies used fire to regulate both plant and animal life. Fire history studies have documented periodic wildland fires ignited by indigenous peoples in North America and Australia. Native Americans frequently used fire to manage natural environments in a way that benefited humans and wildlife, starting low-intensity fires that released nutrients for plants, reduced competition, and consumed excess flammable material that otherwise would eventually fuel high-intensity, catastrophic fires.
Fires, both naturally caused and prescribed, were once part of natural landscapes in many areas. In the US these practices ended in the early 20th century, when federal fire policies were enacted with the goals of suppressing all fires.