What Are Controlled Burns and Why Are They Necessary?

A controlled burn is a fire that is meticulously planned, ignited intentionally, and managed throughout. Also known as prescribed burns, these fires can benefit both people and the environment. Decades of fire suppression, however, have created a backlog of unburned ecosystems. This dangerous buildup of fuel will require careful management to avoid catastrophic fires. 

Controlled Burn Definition

Controlled or prescribed burns are thoroughly planned, intentionally set fires used to manage ecosystems where fire would naturally occur. According to the U.S. National Park Service, "a prescribed fire is a planned fire," and the planning that goes into prescribed burns is extensive.

Before burning, managers must account for the amount of flammable material or "fuel load" in an area, the safety of people and property in the surrounding regions, how weather conditions might affect the fire, and how likely a controlled burn is to meet a set of predetermined goals.

The frequency and intensity of prescribed burns are not arbitrary. Most controlled burns are intended to mimic low-intensity natural fires, which maximizes environmental benefits and minimizes risk. In forests, this means that the fire does not reach the canopy and causes little damage to trees. When fires are suppressed for long periods of time, organic matter builds up, which can prevent certain plants from growing and can fuel bigger fires. 

Both federal and private agencies prescribe fires. Often, these groups work together, employing teams of trained experts to plan, ignite, and oversee the fires. Congress may also get involved by allocating funds for controlled burns, setting targets for areas burned, and setting rules that protect air quality.

Are Controlled Burns Necessary?

Many ecological communities evolved with lightning-ignited fires occurring every few years. Because of this, many plants and animals are specially adapted to cope with fire and depend on burned areas for their survival.

In addition, a controlled burn may be designed to create habitat patches to promote diversity of native species or to help the recovery of threatened or endangered species. For example, seeds of the endangered longleaf pine only germinate on bare soil. In other cases, fires keep invasive plants in check and prevent them from out-competing native vegetation. According to the U.S. Fish and Wildlife Service, fire also creates open habitats for birds like the bobolink to feed and nest. Other animals, including moose, feed on young vegetation that regrows after an area has been burned. 

Fire is also a natural ecosystem cleaner. Over time, woody debris, dried leaves, and other dead plants collect on the ground. The more these flammable materials build up, the larger the next fire, whether prescribed or wild, can be. Prescribing fire for fuel reduction may also be prioritized near population centers in fire-prone areas. Strategic controlled burning could help lower the U.S.’s carbon emissions by 14 million metric tons per year, according to research published in Environmental Science & Technology. Because controlled burns target understory plants and debris, they remove a layer of fuel from the forest and protect large, carbon-rich trees from burning. Wildfires on the other hand burn hotter, kill more trees, and often release significantly more carbon. So, while it may seem counterintuitive, prescribed fires can curb greenhouse gas emissions and help slow climate change

How Do Prescribed Fires Work?

Leading up to a prescribed burn, experts follow a thorough planning process that accounts for the unique characteristics of the area. These plans vary depending on the federal or non-government agency prescribing the fire. For instance, the National Park Service requires fires to be administered according to the specific park’s fire management plan and to have a detailed procedure for each controlled burn. 

To prepare the land for fire, sometimes a fire is prescribed following ecological thinning, in which selected trees, often those that are small or sick, are felled to make a forest less dense. Removing these trees prevents the spread of pests and diseases and keeps fire from traveling up smaller trees to reach the canopy. 

Before burning, fire crews will also make fire breaks (gaps in vegetation or flammable material) to create barriers around the burn area. Then, after a weather check, crews ignite fires with drip torches. Throughout a controlled burn, fire crews will monitor the perimeter to ensure that the fire does not spread.

Broadcast Burning

Broadcast burning is a fire prescription technique that covers large areas with low-intensity fire. Broadcast burns are intended to mimic naturally occurring fires and are generally set to reduce the amount of material available for a wildfire or to restore a habitat.

The USDA reserves the term broadcast burning for areas with little or no canopy, such as prairies or shrublands; however, some groups use the term for ecosystems with and without a canopy. 

Understory Burning

Understory burning is similar to broadcast burning in that it consists of low-intensity fires over large areas. Understory burns are also used to reduce fuel loads on the forest floor in order to minimize the risk of devastating canopy fires.

Longleaf pine ecosystems in the Southeastern U.S. are often prescribed understory burns. The technique creates the patches of bare soil needed for longleaf pines to reproduce, and also prevents invasive grasses from spreading.

Pile Burning

Pile burning occurs in a concentrated area where wood and other flammable materials are stacked and burned. These fires are intended to reduce the fuel load in an area, generally after trees are selectively removed. Pile burns are prescribed in areas where large-scale fires are impractical or altogether impossible, such as national parks. 

Controlled Fires vs. Wildfires 

Unlike meticulously planned controlled burns, wildfires start naturally, accidentally, or by arson. According to the National Fire Protection Association, lightning strikes caused almost 25,000 fires between 2004 and 2008.

Despite often being naturally ignited, wildfires are not without significant human influence. In an area where fire has been absent, there can be a huge buildup of flammable materials, making the wildfire burn hotter and longer than if fires had never been suppressed. Under these circumstances, wildfires can quickly get out of control, devastating huge swaths of forest or grassland. From an ecological perspective, these out-of-control fires can kill large carbon-storing trees, leading to a huge loss of carbon storage.

Uncurbed wildfires also threaten people and property. In 2020, wildfires in California, Oregon, Washington, and Colorado caused an estimated $16.6 billion in property damage.

According to the Center for Climate and Energy Solutions, the climate crisis is raising the risk of dangerous wildfires by making many areas warmer and drier. These ideal fire conditions are extending the fire season in affected areas.

Fire Suppression in the US

Wildfires earned a bad reputation in the U.S. during the early 20th century. This was, in part, prompted by devastating fires that burned across Montana, Idaho, and Washington in 1910 — just five years after the founding of the U.S. Forest Service. These fires, known as the Big Blowup, burned an estimated 3 million acres of land in just two days and smoke from the fires traveled as far as New England. 

These and other tragic fires led land managers, conservationists, and the public to view fires as a danger to ecosystems and people. What followed was decades of policy that favored fire suppression and dramatically changed ecosystems. The country's stance on wildfires had ripples around the world and led many other countries to adopt fire suppression policies.

Air Quality Implications

Fires, whether natural, accidental, or prescribed, can have detrimental effects on air quality — though controlled burns release an estimated 20% of the smoke emitted by wildfires.

When an ecosystem burns, smoke and tiny particles are released into the atmosphere. Inhaling these substances can cause short- and long-term respiratory problems including asthma, chronic obstructive pulmonary disease (COPD), bronchitis, and pneumonia. Unfortunately, many areas with high fire risk are also seeing population growth, which increases the chances of people being affected by fires.