Fire Spread

There are three general patterns of fire spread that are recognized.

example of creeping fire

Creeping ground fire at Grand Canyon National Park, Arizona

example of surface fire

Surface fire at Grand Canyon National Park, Arizona

example of crowning fire

Crown fire at Yellowstone National Park, Wyoming

Types of Fire Spread

Ground fires—which burn organic matter in the soil beneath surface litter and are sustained by glowing combustion.

Surface fires—which spread with a flaming front and burn leaf litter, fallen branches and other fuels located at ground level.

Crown fires—which burn through the top layer of foliage on a tree, known as the canopy or crown fires. Crown fires, the most intense type of fire and often the most difficult to contain, need strong winds, steep slopes and a heavy fuel load to continue burning.

Size and Intensity

Even though fire is a fairly common occurrence, very few fires become extremely large. In the United States, 2 to 3 percent of all fires account for more than 95 percent of the total area burned annually. The blackened plots left behind by these types of large fires contribute to the image of fire as a destroyer of the natural environment. In reality, the opposite is true. A carefully planned prescribed burning program can provide many benefits that enhance the health of an ecosystem.

For example, regular prescribed fires can reduce the amount of ground fuels, thereby lowering the potential for large wildfires. If future wildfires should occur, the fires would be less intense and easier to contain. Fuel reduction can help lessen the possibility of high intensity crown fires. However, in five to eight years enough litter can accumulate in a forest to return ground fuel quantity to the pre-fire level. Therefore, it is important that a regular, planned burning program is followed rather than a single fire event.

High intensity fires can cause as soil destruction, such as loss of nutrients and removal of debris needed to protect seedlings. In areas where such damage occurs, rehabilitation plans are made and actions are taken to reduce further damage and to try to restore the area.

Wildfires are suppressed in developed areas, where people or structures are threatened, or where high fuel levels create a potential for intense fire capable of spreading into areas with these conditions.

Benefits of Fire

Among the other benefits of prescribed burning are:

  • Insect pest control
  • Removal of exotic, or non-native, species that compete with native species for nutrients and other needs
  • Addition of nutrients for trees and other vegetation provided by ashes that remain after a fire
  • Removal of undergrowth, thereby allowing sunlight to reach the forest floor to encourage growth of native species
  • Encourage the growth of fire-dependent species
blue bird eggs in a nest inside a burnt tree

Burned trees can provide nesting sites for birds. Bryce Canyon National Park, Utah.

After a Fire

Furthermore, a burned tree is not wasted. It can provide nesting sites for birds, homes for small mammals and a base from which new plants can grow. When the dead tree begins to decay, it releases nutrients into the soil, enhancing growth of surrounding flora.

The benefits or harm derived from fire can vary greatly from one plant community to another. In the United States, all ecosystems have been affected to some degree by fire.