Blazing forest: what's sparking the infernos?

This May, wildfires churned out columns of billowing smoke, signaling an early start to California's fire season. For firefighters, they were a burning reminder of last year, when forest fires torched a total of 3,000 square kilometers (750,000 acres) of land--an area bigger than Rhode Island!

Now, scientists fear that fires across the U.S. are becoming more destructive. "The fires happening today are much more severe than they were in the past. And they're burning more fuel," says Scott Stephens, a fire scientist at the University of California at Berkeley.

FIRE FACTOR

Why have recent chars been so damaging? One reason: too much fuel--such as dry twigs and leaves--that ignites when heated. Many forests, like California's Ponderosa pine stands, are adapted to burn naturally, on a small scale, every 10 to 15 years, says Stephens. These tiny torches clear debris and small trees.

But since 1910, firefighters have smothered these fires to protect nearby homes. "When fires are suppressed, we have fuel buildup," explains Nate Hesse, a California smokejumper (see "Flame Fighter," left). Once a fire does ignite, the dense forest makes for a hotter fire.

HOT AND BUGGY

Another culprit for the fires in the West: unusually low rainfall, or drought. The bone-dry weather has wicked moisture from trees, making them more flammable (able to burn quickly), says Hesse.

And thirsty trees in Southern California are falling victim to bark beetles. These critters clog the phloem, or tissue that carries water from a tree's roots to its branches. Without water, the tree dies.

Sometimes the dead trees stay standing, spelling trouble during a wildfire. Haines sweep up the dead trees and into the forest's canopy (top portion of trees). These treetop blazes, or crown fires, spread rapidly by jumping from canopy to canopy.

FLAME PROOF

To help prevent infernos. foresters are setting controlled fires in dense forests. That way there's less fuel to burn, says Hesse.

ANATOMY OF A WILDFIRE

Igniting a forest fire requires only three ingredients: extreme heat, oxygen, and fuel (material that releases energy when heated), such as dry twigs and leaves. Once the ingredients spark a blaze, an intense wildfire can travel at speeds of up to 14 kilometers (9 miles) per hour, torching everything in its path. How does a wildfire spread? Read on.

1. UP IN SMOKE

The first sign of a wildfire is a plume of smoke. The hot gases rise because they're less dense (amount of matter in a given volume) than surrounding air.

2. FRESH AIR

Cooler air from below sweeps in to replace the rising column of blistering-hot gases. As the cool wind swooshes in to fill the void, it brings more oxygen--a necessary ingredient for fire.

3. FIERY WIND

The fresh air doesn't stay cool for long. The fire's sizzling flames heat the incoming air through convection (movement of heat in a liquid or gas). And as fresh air continues to rush in and take the place of the rising smoke, the sweeping air can create strong winds.

4. UPHILL SCORCH

Forest fires sweep quickly up hills. That's because the rising smoke and warmth of the fire preheat a mountain's trees and other vegetation. By the time the flames jump to these spots, the fuel is already hot and brittle--perfect for getting torched.

5. FLAME FIGHTER

Firefighters called smoke. jumpers parachute into remote, blazing forests. Their job: stop fires before they get out of control.

6. JUMPING FLAMES

A fire's strong winds can blow embers (burning particles of wood) far away. That enables a fire to jump barriers, like rivers and creeks. When the glowing embers land, they can create smaller fires called spot fires.

Year   Wildfires   Acres Burned

2000    122,827     8,422,237
1990    122,763     5,452,874
1980    234,892     5,260,825
1970    121,736     3,278,565
1960    103,387     4,478,188

Source: National Interagency Fire Center:
www.nifc.gov/stats/wildlandfirestats.html

DID YOU KNOW?

* Smokejumpers are considered "firefighters from the sky." They parachute into hard-to-reach wildfires. To qualify for this strenuous job, the applicant must be able to do 7 pull-ups, 25 push-ups, 45 sit-ups, and have one year of wildfire-fighting experience.

* One of the worst wildfires in history was the Peshtigo fire in Wisconsin and Michigan in 1871. It destroyed more than 3,780,000 acres and killed more than 1,500 people.

* Many wildfires are started by lightning strikes. Up to 8 million lightning bolts strike Earth on a typical day!

CRITICAL THINKING:

* Some wildfires that are deliberately set (prescribed or controlled fires) turn into uncontrollable blazes. Research and stage a debate about the merits of prescribed fires.

CROSS-CURRICULAR CONNECTIONS:

ART: Create a wildfire-safety poster.

RESOURCES

* Grolier search term: Forest Fire

* Play a smokejumper at; www.smokeybear.com/kids/games_smoke.asp

* For curriculum and hands-on activity ideas, visit: www.firelab.org/fislhome.htm

DIRECTIONS: Fill in the blanks to complete the sentences.

1. Wildfires can be aggravated when conditions are dry, such as during periods of unusually low rainfall known as --.

2. Crown fires occur far above the ground when flames jump from one -- of a tree to another.

3. Foresters sometimes deliberately set -- in forests to avoid the accumulation of -- and --, which are fuels for forest fires.

4. Hot gases rise because they are less -- than surrounding air.

5. -- parachute into remote, blazing forests to fight fires.

Answer

1. drought 2. canopy 3. controlled fires, dry twigs, leaves 4. dense 5. smokejumpers

FIERY NUMBERS

In "Blazing Forests" (p. 12), you learned that wildfire management is no easy task. To understand the extent of wildfire destruction, experts keep track of the number of blazes and the total area burned each year in the U.S. Below is a chart showing the data for five select years. Use the information in the chart to answer the questions that follow. Use complete sentences.

1. According to the chart above, which year had the greatest number of wildfires? Which year had the fewest?

2. Which of the above years experienced the most fire damage?

3. How many more acres of land were burned in 2000 than in 1960?

4. What was the average number of acres burned in each fire of 1990?

5. In the year 2000, it cost government agencies approximately $1.4 billion to suppress fires. Using that estimate, about how much did it cost to suppress fire for each acre of land that year?

6. On a separate piece of paper, create a double bar graph. Use the above data to show the number of wildfires, along with the number of acres burned, for the selected years. Hint: Use two y-axes--one on each side of the graph. Have one represent the number of fires and the other represent acres burned.

Take It Further: Study the pattern on your graph. What other data might be collected to assess more accurately the extent of wildfire damages in the United States?

Answer

1. The greatest number of wildfires occurred in 1980. The fewest number of wildfires occurred in 1960.

2. The year 2000 experienced the most fire damage.

3. 3,944,049 more acres of land were burned in the year 2000 than in 1960.

4. The average number of acres burned in each fire of 1990 was approximately 44.41 acres.

5. It cost approximately $166 to suppress one acre of wildfire in 2000.