Fire Science

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Prescribed Fires | Fire Behavior | Fire FAQs  |

Since the beginning of time, fires have burned in the forests of Arkansas and Oklahoma, playing a vital role in keeping the land healthy. Fire reduces dead vegetation, replenishes nutrients in the soil, stimulates new growth, and maintains biological diversity. As civilization moved deeper into the forest, fire came to be seen as an enemy that destroyed lives, property and natural resources. As a result, the nation demanded that the Forest Service exclude fire from our environment, and we were mostly successful for decades.

Over time, it became apparent that our success had many unforeseen consequences. Without fire, our forests became overcrowded and vulnerable to attacks by insects and disease.

Today, we know that fire is essential to the health of our forest. Since conditions in many areas are conducive to large, severe wildland fires, and because so many people now live in or near forests, we need fires to burn in a more controlled way than is usually possible when they are caused by naturally occurring events such as lightning strikes. In order to restore fire to its natural role in the forest, we ignite prescribed fires in the spring and fall when conditions allow for slow, low intensity burning.

Forest Service fights fire by starting a few - Feature story

Glossary of fire terms commonly used.

Prescribed Fires

Our forests need fire. By igniting prescribed fires, we can maximize the chance that they will burn on our terms with acceptable effects. Or, we can wait until they burn on their own terms, with no control over the effects. The choice is ours.

Prescribed fire is used to approximate the natural vegetative disturbance of periodic fire occurrence. This vegetative management tool is used to maintain fire dependent ecosystems and restore those outside their natural balance. Generally, low intensity prescribed fire, is applied by trained experts to clear ground of dangerous fuels like dead wood and brush. This low-intensity fire is vital to the life cycles of fire-dependent range and forest lands.

Most prescribed fires are lit by crews using the drip torch, a hand-carried device that pours out a small stream of burning fuel. Other fires or burns are ignited by helicopters carrying a gelled fuel torch (helitorch) or a sphere dispenser machine that drops material to ignite the surface fuels in forest and range types.

Exactly how each unit is ignited depends on weather, the lay of the land, and the intensity of the fire needed to meet the goal of the burn.

 

Benefits:

• Reducing fuel build-up
• Dead wood, overcrowded, unhealthy trees, and thick layers of pine needles can all contribute to catastrophic wildfires including crown fires.
• Prepares the land for new growth
• When excess vegetation or needle layers are burned off, nitrogen and other nutrients are released into the soil and become available for new plants to grow.
• Helps certain plants/trees germinate
• Many native plant and forest communities have adapted to fire for their germination and growth. Seed contact with soil (such as that exposed by a fire) is necessary for some species to naturally regenerate.
• Naturally thins overcrowded forests
• Historically, natural fire thinned the forests. Thinned forests can recover faster and are more resistant to insect and disease attacks. Currently, many of the mature forests are overcrowded, resulting in a lack of vigor and health.
• Creates diversity needed by wildlife
• Fire provides diverse habitat for plants and animals. Grazing wildlife such as elk and deer benefit from new growth as shrubs produce edible leaves when re-sprouting after a fire. 

Learn more...
 

Fire Behavior

Fire behavior is influenced by three primary environmental factors. These are fuel, weather, and topography.

Fuel: The material that ignites and supports combustion. On the National Forests in Arkansas and Oklahoma, the fuel is primarily pine needles and hardwood leaf litter on the forest floor. The continuity, arrangement, and fuel bed depth all influence fire intensity. The moisture content of the fuels is the principle factor determining whether they are available for combustion. Small fuels (leaves, needles, grass) respond most quickly to changes in temperature and humidity. Large fuels (branches, logs) are most effected by periods of drought after which they can significantly increase fire severity.

Weather: Weather is typically the most critical factor influencing fire intensity and spread. Temperature, relative humidity, precipitation, and wind all effect the moisture content of the fuels, influencing availability. Additionally, wind provides the oxygen needed to sustain combustion, as well as most of the energy needed for fire spread. Weather is constantly changing, making it the most difficult of the environmental factors to predict. The National Forests in Arkansas and Oklahoma and its cooperators maintain a network of fire weather stations in and around the two states which help us to determine fire danger and potential fire behavior.

Topography: Topography refers to the landscape of a given area. Steep slopes offer greater potential for increased fire intensity than flat ground. Additionally, steep slopes make fire suppression more difficult by limiting strategies and tactics which can be utilized. South and southwest facing slopes typically will have lower fuel moisture regimes as a result of solar heating.
Topographic features which channel wind and heat energy such as chutes, saddles, and box canyons all are potentially dangerous situations for firefighters.
By understanding the relationships between fuels, weather, and topography, fire management professionals can utilize computer programs to "model" and predict fire behavior. With this knowledge, fire suppression tactics can be adjusted to best meet objectives while maximizing the safety of firefighters and the public.

Fire FAQs

Wildfires often begin unnoticed. They can spread quickly, igniting brush, trees and homes. Reduce your risk by preparing now, before wildfire strikes. Meet with your family to decide what to do and where to go if wildfires threaten your area.

Visit http://www.firewise.org/ for more information

Is my home at risk for wildfire?

The land use in your area and the type of vegetation around your home contributes to wildfire risk. Living in a woodland setting, in or near rural areas is also a risk factor.

What are the top causes of wildfires in Arkansas and Oklahoma?

People start most wildfires. In Arkansas and Oklahoma, arson is the number one cause of wildfires. Escaped debris burning, carelessly discarded smoking materials and lightning are also causes.

What should I do before wildfire threatens?

Design and landscape your home with wildfire safety in mind. Plan fire-resistant shrubs and trees. Create a defensible space around your home. Use fire-resistant roof and exterior construction. Or treat wood or combustible material used in roofs, siding, decking or trim with UL-approved fire retardant chemicals. Create a disaster plan. Make sure your house number is easy to read on your home.

What is defensible space?

It is at least 30 feet of lean, clean and green space surrounding your home. This space gives firefighters room to put out fires.

How do I create a defensible space?

Make your yard lean by pruning shrubs and tree branches within 15 feet of your chimney or stovepipe. Remove dead tree branches that extend over the roof. Make your yard clean by raking leaves and removing dead tree limbs and twigs. Stack firewood at least 100 feet away from your home. Make your yard green by removing flammable vegetation and replacing it with fire-resistant plants.

What types of plants are fire resistant?

Dogwood, viburnum, redbud, sycamore, magnolia, beauty berry, oaks, red maple, wild azalea, sweet gum, coontie, winged elm, black cherry, persimmon, wild plum, sugarberry, Florida soapberry, fringe tree, ferns, wild olive, blue beech, hop hornbeam and sparkleberry.

What type of roof construction is fire-resistant?

Class-A asphalt shingles, metal, cement and concrete products help resist fires. Added protection is a fire-resistant sub-roof.

What type of exterior construction is fire-resistant?

Fire-resistant wall materials are cement, plaster, stucco and concrete masonry. Windows that are double paned glass can also help a home be more resistant to heat and flames.