Eldorado National Forest

Fire & Aviation: Prescribed Fire

Fuels in your National Forest Fire has been a natural part of the Sierra Nevada ecosystem for a very long time. Throughout time wildfires ignited and burned naturally through the forest. Some were caused by lightning and some were intentionally started by Native Americans. These low intensity fires in the past kept the forest floor free from the natural annual build up of tree needles, dead grass, thick brush, and dead trees. As a result, fire has shaped vegetation patterns and wildlife distributions in the National Forests. The next time you are camping, hiking or driving in your National Forest notice how much limb wood, brush, and dense thickets of small trees cover the forest floor. This build up of fuel feeds wildfires.

Today, fires that are not caught when they are small quickly build in size and fire intensity into catastrophic wildfires. The USDA Forest Service uses prescribe burning as its way to put fire back into the ecosystem. As you read on you'll discover the value of prescribe burning in your National Forests.

Nature's way of recycling

Fallen trees and limbs left to rot on the Forest floor will decay at a very slow rate. In fact, large logs can take more than 100 years to decompose. This process is aided by the numerous species of bacteria, insects, and wildlife that live in the decomposing materials. All this rotting is one way that nature recycles nutrients back into the soil. Pine needles decompose very slowly. It takes more than a year for 10% of the pine needles to decay. As a result, year after year, pine needles continue to build up until they are eliminated by fire.

Faster recycling occurs during a fire. Gasses are released into the atmosphere in the form of smoke. In the burned area, nitrogen and other nutrients remain and are leached back into the soil as rain soaks the ground. This is nature's way of rapidly recycling nutrients.

Unfortunately, when there's too much fuel on the ground and it's burned in an intense wildfire these benefits are often missing. Intense fires tend to scorch the ground and kill the trees above.

Which is better, slow or fast recycling?

Slowly decomposing materials release nutrients steadily into the soil. This continuous release helps to maintain growth over a long period of time. Decomposition can last indefinitely as long as dead material on the forest floor continues to accumulate. In other areas of the world, a wildfire may happen once every 600 years. in these areas, only decomposition will supply needed nutrients between wildfires.

Wildfires cause fast nutrient recycling. An abundant supply of nutrients helps new seedlings, brush, and grasses to grow quickly and become established following a wildfire. This is nature's way of quick starting a forest. Most of the nutrients are quickly used up; however, more lasting effects occur when they are leached into the soil. It usually takes a few years for the supply of nutrients to return to normal levels.

The forest needs both slow recycling, from decomposition, and fast recycling from fires. However, fires ignited at the wrong time can quickly turn into catastrophic events.

Wildfires occurred every seven to 25 years in Sierra Nevada forests prior to the early 1900s. Around 1915 National Forest management policy viewed wildfires as destructive and began putting them all out as quickly as possible. Today we realize the important role fire plays in maintaining healthy National Forests.

Why not prescribe burn everywhere?

Some places are not easy to prescribe burn. These are locations where it may not be economical, feasible, or practical. Exact fire prescriptions are developed by fire managers before burning is allowed. These fire prescriptions are based on weather, moisture content of the fuels, and how the fire can be lighted (ignition patterns). There may only be 50 days in an entire year when an area meets the prescription.

Laws and regulations also determine when a prescribe fire may be ignited. Air quality regulations play an important role. It's not unusual for forest conditions to be in prescription and a no burn day due to poor air quality. Prescribe burning takes place when laws, regulations, and forest needs are all in balance. Prescribe burns also don't take place when there are safety, health, and esthetic concerns.

The Sierra Nevada ecosystem was developed with fire as one of the main sculptors of vegetation found there. Fire related processes need to continue to perpetuate this ecosystem. Please take time to learn more about ecosystem management in your National Forests.

USDA Forest Service - Eldorado National Forest
Last Modified: Friday, 28 January 2005 at 15:13:20 EST