What is a controlled burn? Wildfire and forest health terms to know

The Republic | azcentral.com
Flames lick at the base of a tree in the Prescott National Forest. The Stubbs Fire was ignited by lightning but managed as a prescribed burn.

If you drive into the high country during the spring or fall months, you've probably seen a sign warning of smoke from a prescribed burn. It's a fire and it's burning somewhere nearby, but it's not a wildfire.

During a wildfire, you may hear about a Type 2 team or the level of containment. And afterward, you may read about efforts to thin unburned forests to prevent future fires. What do all these terms really mean?

Here are a few of the key phrases you should know:

Prescribed fire, or controlled burn

A fire managed by authorities to meet pre-set goals related to forest health, habitat improvement or the disposal of debris, vegetation or potential fuel. A plan that meets environmental and safety concerns is put in place before a fire is set. In some cases, authorities may decide to manage a fire started by lightning using a plan developed for the location.

RELATED:A wildfire becomes an ally in restoring forest health


A fire is contained when a fuel break surrounds the fire. A fuel break is generally a line built by fire managers but could be a natural barrier.


A fire is controlled when flames are extinguished and the fire line is strong enough to prevent any flare-ups from escaping.

Defensible space

An area where potential fuel for a fire has been removed, reduced or treated in a way to keep it from burning. Defensible space around a home, for example, is meant to keep fires from reaching the structure. Defensible space can also act as a barrier. The U.S. Forest Service generally defines defensible space as an area at least 30 feet around a structure where fuel or other vegetation has been removed.

Crown fire

A crown fire develops when flames move from the ground level up through a tree or shrub into the tops or crowns of the vegetation. Flames in a crown fire can move through a forest more quickly than flames burning on the ground. A crown fire occurs more readily when trees are growing too close to each other, creating a "ladder" for flames.

Forest thinning

When a forest has grown too dense, managers develop a plan to remove trees or other vegetation. Removing trees can help improve the health of the remaining trees and encourage the growth of more diverse vegetation at the ground level. A less-crowded forest also reduces the risk of catastrophic wildfires.


The Four Forests Restoration Initiative is a project led by the U.S. Forest Service to thin overgrown forests in four of Arizona's national forests: the Coconino, Kaibab, Tonto and Apache-Sitgreaves. The goals are to promote healthier forests with more diverse vegetation, restore natural wildfire cycles, protect communities in the forests and help local economies by providing materials for timber production.

Incident commands

When an agency begins its work on a wildfire, an incident management team is established. The type of team, its make-up and the equipment brought in depend on the fire's size, location, local conditions and other factors. The earliest teams are often made up of local firefighters. A Type 3 or Type 2 team would bring in resources from the state and national level. A Type 1 team is established for the worst fires and includes state and national resources, as well as specially trained units such as hotshot teams. Aircraft and other equipment are made available in greater numbers for the largest response teams.

Firefighting aircraft

Firefighting agencies employ different types of aircraft spending on the fire, its location, its intensity and local conditions. A lead plane will check conditions and report back with sites most in need of help. An air tanker is a fixed-wing aircraft used to drop suppressants. Helicopters are used to drop buckets of water or suppressants and can be used to move crews.