Fire-Past Tense
In 1988, fires raged through Yellowstone National Park in Wyoming. Scores of fire fighters from the U.S. Forest Service, state forestry agencies, and even the U.S. Army battled blazes. The fires burned close to a million acres in and around the park. This is more than half the total land area of Yellowstone Park, although the damage was not as severe as this figure indicates, since the fire burned in a mosaic pattern and left much of the "burned" area untouched or only lightly burned.
How do fires as catastrophic as this get started? How could forest managers prevent these fires? Are fires bad or good for the forest? The answers to these questions require a basic understanding of fire behavior.
The Fire Triangle
Fire is a chemical reaction that requires three main ingredients:
- fuel (carbon)
- oxygen
- heat
These three ingredients make up the fire triangle. If any one is not present, a fire will not burn.
Fuel generally is available in ample quantities in the forest. Fuel must contain carbon. It comes from living or dead plant materials (organic matter). Trees and branches lying on the ground are a major source of fuel in a forest. Such fuel can accumulate gradually as trees in the stand die. Fuel also can build up in large amounts after catastrophic events, such as insect infestations or disease. Trees and branches left on the ground after a logging operation can become fuel too. In Yellowstone an insect infestation (pine bark beetle) in the early 1980s killed many trees, providing a buildup of fuel.
Oxygen is present in the air. As oxygen is used up by fire, it is replenished quickly by wind.
Heat is needed to start and maintain a fire. Heat can be supplied by nature through lightning. People also supply a heat source through misuse of matches, campfires, trash fires, and cigarettes. Logging equipment, trains, and automobile exhaust systems also can supply a heat source for fire. Once fire has started, it provides its own heat source as it spreads.
Three Faces of a Fire
There are three types of forest fires: surface, crown, and ground.
Surface fires burn twigs, needles, leaves, branches, and underbrush on the forest floor. They rarely kill large trees directly, but they do kill seedlings and young saplings. Surface fires are the most common type of forest fire in the eastern and southern United States, especially in hardwood forests.
Crown fires are the most spectacular. They occur when high winds and dry materials make conditions right for rapid fire spread. Surface fires move into the tree crowns, often by climbing a fuel "ladder." These fires can spread rapidly from crown to crown, and surface fires often follow right behind them. Crown fires produce tremendous heat, often causing extensive damage to trees. Crown fires usually occur in conifer forests (e.g., pine, spruce, and Douglas fir) and are most common in the western United States.
Ground fires, although not as visible as crown fires or surface fires, can damage the soil. Ground fires burn in soils high in organic matter (e.g., peat, leaves, tree roots) and can burn beneath the litter layer. They burn very slowly but generate a large amount of heat, usually killing all the trees in their path. Ground fires are common in the northern forests of Minnesota, especially in peat soils.
Fire Control
Once a fire starts, fire fighters control it by "breaking" one leg of the fire triangle. This means that one of the necessary ingredients for maintaining fire-fuel, oxygen, or
heat—must be eliminated.
To break the fuel leg, a fire fighter might:
- build a fire line by removing all fuel down to the bare soil in a band in front of the advancing fire. This can be done by hand with tools known as scalpers, or with bulldozers and other heavy equipment.
- light a backfire. A backfire is a fire deliberately set by fire fighters that burns all the fuel backward toward the fire. This stops the advancing fire by eliminating fuel in its path.
To break the oxygen leg, a fire fighter might:
- cover burning fuel with soil, using hand tools or bulldozers.
To break the heat leg, a fire fighter might:
- soak high-value buildings with water or with a
water/foam mixture. Water absorbs heat and prevents the fuel from heating up to the temperature at which it will burn.
- dump fire retardant on the fire from an airplane. A retardant will cool down the fuel.
- in the case of ground fires, inject water into the ground to cool the fuel.
- separate fuels and break them apart to diffuse the heat.
- cut down and break apart tall, burning, dead trees to remove a source of airborne sparks.
Fire Prevention
Foresters have one other important method of breaking the fire triangle. They "attack" the fire before it starts with fire prevention measures.
Fire Prevention Rules for Woodland Owners
- Maintain a cleared firebreak around your woodland. Make sure the firebreak is cleared to bare mineral soil. Although the firebreak may not stop a fire, it provides a good starting place for fire suppression crews to build larger lines.
- If your woodland is larger than 20 acres, construct some trails or roads to provide better access to all areas and to break it into smaller units.
- Thin and prune pine and spruce-fir stands. If you don't, these trees can form a fuel ladder that lets surface fires climb into tree crowns. Adding buffer strips of hardwoods to stands is also helpful, since fire does not carry as well in hardwoods.
- Chip or break up slash left on the ground from logging so that it decays faster.
- Remember, education can be more powerful than a bulldozer in fighting forest fires. Spread the word about fire safety measures.
Fire Weather
Weather is the major factor affecting the fire triangle. In the Yellowstone fire, weather conditions contributed to the fire's ferocity.
High temperatures and dry air lower the amount of moisture in fuels, making them ignite and burn more easily. In the Yellowstone fire, fuels had a two percent moisture content, an extremely low reading.
Wind also contributes to fire. Strong winds help dry out forest fuels. After a fire has started, winds bring in new oxygen to replace that which the fire has used. The wind also helps a fire spread by pushing it. In Yellowstone, winds were gusting 50 to 70 miles per hour, with steady winds of 40 miles per hour.
Storms affect the likelihood of fire, too. Lightning can cause fires when it strikes trees or dry grass. Fewer fires occur in years with abundant rainfall than in dry years. During wet years, plants remain green and do not ignite or burn well. In 1988, Yellowstone was experiencing its worst drought in 120 years of recorded weather history.
Fire—Friend or Enemy?
Fire plays an important role in shaping the composition of forests. Fires that occurred more than a century ago affect the appearance of our forests and prairies today. Many of the aspen and jack pine forests today in the Lake States are the direct result of forest fires 20 to 100 years ago.
Fire that is not controlled or managed properly creates problems. Not only can it kill trees, but also it can damage them in other ways. Trees that survive a major fire may be scarred, creating an entry point for insects and diseases. When weakened by fire, trees are less able to fight off insect or disease attacks.
Still, fires perform several needed functions in forests, so foresters speak of "fire management" as well as "fire prevention." If we were to eliminate all fires from a forest, fuels would build up, and eventually a very disastrous fire could take place. This happened in Yellowstone in 1988.
Click here for Answers to Quiz
Foresters often set surface fires to help reduce the amount of fuel present and thus prevent major fires. In the southern United States, foresters set fires every two or three years to reduce unwanted understory vegetation in pine forests and to control tree diseases. Fires are set in recently logged areas to remove debris and prepare the site for replanting.
Fire helps some tree species reproduce. Jack pine, for example, has serotinous cones, which don't open and release their seeds until they are exposed to a heat source such as fire. Fire helps other seeds get started by killing competing vegetation and removing dry litter on the soil surface to expose moist mineral soil.
Fires also improve the habitat for some wildlife. Fires create forest openings and maintain shrubs for wildlife food and shelter.
The changes brought by fire are not always bad. The Yellowstone fires blackened land, killed trees, and destroyed certain animal habitats. But the forest is a renewable resource. These charred, blackened areas already are developing into meadows and regenerating their lodgepole pine and aspen stands. The habitats that were destroyed will be gradually replaced by new habitats for new animals. Yellowstone is undergoing a renewal, the birth of the next 100 years.
Career Considerations
A forest fire fighter is specially trained to suppress fires. Often, the fire fighter will be a forester or forest technician. The fire fighter can expect long days and long nights of work during fire season. Fighting a forest fire requires knowledge of fire behavior, endurance, alertness, good physical condition, and speed. A fire fighter digs fire line, chases hot spots, uses water packs or hoses, and wields a chainsaw in the battle against blazes. The work is hard, but very exciting. A two- or four-year forestry or forest technician degree is a good background for entering this field.
EnviroQuotes
"But the main thing is, folks just hate to see the park change. They think it's being ruined. People have a tendency to want things as they are, but in nature nothing stays as it
is. . . . Nature is hollering, 'I'm getting ready to start over!' We'd like to shout, 'No! Not now! We're not ready for you!' But that ain't the way it works, folks . . . ." John Krebs, a fire behavior analyst, on the 1988 Yellowstone fire in Journal of Forestry, December 1989.
Tree-vial Pursuit
More than $145 million was spent to suppress the Yellowstone area fires in 1988.
CHALLENGE!
You're J. Gold Flash, a homeowner in the hills of Santa Monica, California. Your six-year-old home is constructed of ponderosa pine logs with cedar shake roofing. You have carefully placed your home so that you are surrounded by towering pines on all sides. Your landscape is natural-you don't mow the grass or weeds, and you let pine needles and branches stay where they fall. Tree branches are not pruned, and several branches lay softly touching your roof. A two-year supply of firewood has been cut and is stacked neatly next to your home, ready to fuel your handcrafted stone fireplace. Because you value your privacy, you don't display your name or address at the end of your driveway. The driveway itself is single lane, narrow, and winding-the better to keep trespassers out.
You've just heard on the radio that a nearby fire is burning out of control, and threatens your home and the homes in your neighborhood. The radio warns that you have approximately four hours to evacuate, and that you can safely spend three hours trying to save your home.
To save your home, what leg of the fire triangle should you concentrate on breaking? What specific action could you take? What could you have done six years ago when you were constructing your home to make it safer?
Minnesota State Fair
4-H Forest Resource Premium List rules are:
- The exhibit should not exceed 12" deep x 18" wide x 22" high.
- Exhibits should include a project title and your name.
See the booklet State Fair Premium Guidelines, available from your
local county extension agent, for information.
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Tips For Making A Three-Sided Display:
- It's a good idea to get your leader, parent, or other adult to help you.
- Use a material such as hardboard, particleboard, or plywood. Posterboard is not sturdy.
- Open displayed dimensions should not exceed 12 inches deep by 18 inches wide by 22 inches high.
- Use hinges to attach the sections to each other.
- Paint or cover the background with adhesive paper, if you'd like.
YEARNING TO LEARN . . .
Additional Activities
In the following activities, remember the basic rules of conservation. Do not damage or destroy the plants and animals you are studying. Leave all ecosystems unchanged. Have a positive impact on the forest.
Take part in a fire prevention campaign in your community or 4-H club. Wildfires burn not only forests and prairies, but also homes and other buildings. Prepare a plan for this campaign. Give a demonstration on fire prevention to your club using charts, posters, slides, or film.
Make your own charcoal, under a leader's or parent's guidance. In a barbecue grill or campfire bed, start a fire using wood chips two to three inches in diameter. When the fire is blazing hot, cover it with soil. After six hours or more, dig up the burned wood. The wood should be charcoal. Restart the charcoal, again under a leader's supervision, and cook some hot dogs or marshmallows! Be sure to fully extinguish the fire before you leave the area.
Burn some forest debris, under a leader's or parent's supervision. In a charcoal grill or campfire ring, try to ignite and burn:
- green pine needles (wet)
- dry, dead pine needles
- green leaves
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- brown, dead leaves
- peat
- rocks
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and other forest debris. Observe how different fuels burn, and whether all forest fuels can be easily ignited.
Make a poster to teach fire education or safety to the public. The poster should be colorful and should emphasize a fire safety issue. Your poster should concentrate on fire source and prevention, (e.g., using spark arresters on chainsaws in forested areas) or fuels (e.g., how to reduce burnable fuels in home/lake cabin yards).
Exhibits/Fair Projects
Prepare a display showing correct uses of fire to improve a forest. The display should contain at least three photographs or drawings of these activities, and should be displayed on a three-sided display board. Each picture should be appropriately captioned.
Prepare a display showing a low fire hazard forest area and a high fire hazard forest area (use photos or drawings). Show four methods of preventing or controlling fires and how each method affects a leg of the fire triangle. Use either a three dimensional display mounted on plywood or in a box, or a three-sided display panel.
Burn at least six different types of pine cones, under a parent's or leader's supervision, in a small grill or campfire ring. Extract the cones from the fire with tongs or a similar instrument before they burn completely. You are trying to simulate a ground fire, which moves quickly. Also, place six cones from the same species in the hot sun for three to five days. Mount the cones on plywood with proper species identification. Summarize what happened to each cone, and indicate whether you believe the cone is serotinous.
Make a poster to teach a concept of fire safety, as suggested in "Additional Activities" above. The poster should be approximately 18 inches by 36 inches.
Make a Wildlife/Wildfire game. Design and build a board game that tells participants where animals go during a fire. For example, bears and elk move out of the way of fires. Animals such as mice and ground squirrels burrow underground. Snakes survive if they can crawl into a hole. Fish stay in streams, which aren't heated by the fire. Animals such as porcupines don't burrow or run fast-they might not survive a fire. Be sure to have rules and a way to determine who wins the game.
Make a historical display of fire activity in your area. Using photos or evidence of fire such as burned bark (fire scars), diagram the history of fire in your town or surrounding area. Your local historical society and library can help you with the information.
Pick a tree species and show how fire helps or hurts the species. Make a display showing a forest before and after a fire. Show how this species is either eradicated or encouraged by fire. Show any special fire-related features of the species, such as thick bark (red pine) or serotinous cones (jack pine). Use a plywood board and three dimensional display or three-sided panel board.
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