Prescribed Burn: How To Do Controlled Fires Safely

Controlled burns are widely applied in forest management; the time and frequency of prescribed events depend on their purposes. There are various reasons why controlled burning is good, but it is also challenging for foresters. In particular, flame escapes are among the most significant disadvantages of this method.

However, deep expertise, weather analytics, and proper situation control help mitigate the risk, while satellite technologies assist in prescribed fire management and forest monitoring.

What Is A Prescribed Burn?

Controlled burn is an intentional setting of forest areas on fire for ‘prescribed’ treatment, hence the term derives. Since the whole process should be thoroughly scheduled and managed, it is also called planned or controlled burning. Applying the prescribed ignition method, foresters must consider:

• area specifics,
• weather conditions,
• public health issues,
• work safety,
• purpose,
• the most appropriate time.

The burnt materials are called fuels and typically include dead vegetation, plant parts affected by tree diseases, or wood remnants after timber harvesting.

Controlled Burning Techniques

The most common types of prescribed forest fires are categorized according to the area covered and fall into broadcast or pile burning. Controlled broadcast burns are conducted on the whole forest area (from a few ha to several thousand ha). Controlled pile burns suggest collecting fuels in stacks (piles) and burning them separately.

Depending on the correlation of spreading flames to wind and if it occurs up or down the slope, there are the following prescribed fire types:

• backing fires,
• head fires,
• trip-head fires,
• flanking fires,
• point-source fires,
• ring fires.

Backing Fires

Prescribed backing fire is ignited against the wind, so it moves slower, compared to other types. The relative ease of control explains the frequency of use. Because it spreads slower, the event takes longer and requires more understory fuels.

Prescribed backing fires are important in combination with other controlled burning techniques to secure safety zones that won’t ignite because all fuels have already been used there.

Head Fires

This type goes upslope or windward, so it spreads fast and produces intensive heat. Prescribed head fires have long flames. Due to its high intensity and fast speed, such controlled forest burn belongs to the most difficult types and demands extreme caution.

Strip-Heading Fires

Strip-heading prescribed burn bases on backing fire or firebreak with ignited strips located one by one. Controlled burn is arranged in the upwind direction from the backing fire zone or firebreak. The distance between the prescribed strips usually varies from 20 to 50 feet and is determined to ensure the timely dissipation of the flames.

Flanking Fires

A flanking prescribed burn in a forest is arranged in controlled lines, making flanks (i.e. parallel) to the wind. Thus, the flames move into the wind. The outer controlled flanks should have firebreaks for safety reasons, to avoid flame escapes. Prescribed flanking fires spread rather fast.

Point-Source Fires

Controlled burns in forests may be inflamed in a grid pattern to reduce the flame intensity and get better control due to unpredicted weather changes. The grid distances and ignition schedule vary depending on the desired flame intensity and allow adapting to changing fuel composition and weather conditions if necessary.

Ring Fires

Ring prescribed fire is set in the form of a circle, starting from the perimeter and moving toward the circle’s center. Controlled ring fire requires firebreaks or blackened zones, surrounding the territory, and deep personnel expertise, as the flames may escape to neighboring stands and agricultural fields. Prescribed ring fires produce relatively low smoke, so they are used when avoiding high smoke production is critical (e.g., nearby kindergartens, residential areas, schools, hospitals, airports, etc.).

How To Do A Controlled Burn

To achieve the best results, prescribed burns in forest management should be thoroughly planned and controlled. It is important to get all paperwork, permits, and licensing done in advance. Also, consider the following circumstances when the situation may get out of control:

• prescribed burn equipment is misused;
• flames spread too fast or too slow;
• smoke annoys the neighborhood;
• controlled burn schedule is developed poorly;
• firebreaks are insufficient;
• fire-managing personnel is not enough;
• controlled burn tools are missing;
• weather forecasts promise low humidity and strong gusts of wind;
• topographic specifics and fuel types are overlooked.

What Are The Best Prescribed Burn Weather Conditions?

Based on the experience of successful controlled burns implementation, the best weather conditions for prescribed burns are as follows:

Weather condition	Recommended value
Air temperature	40-60 degrees F
Relative humidity	40-55%
Surface wind speed	1-3 mph
Transport wind speed	6-18 mph
Precipitation	1 inch

When planning how to do a prescribed burn, it is important to understand the weather’s impact on the intensity and spread of controlled fire.

• Air temperature. The higher the temperature, the quicker combustion. Therefore, it is prohibited to conduct a prescribed burn during the period of droughts.
• Wind. Wind speed and direction must be stable to avoid flame escapes, and the transport wind speed (20 feet above the earth’s surface) must be strong enough to ensure proper smoke dispersion.
  Stability of air masses. Vertical airflows impact smoke transportation. When air masses are too stable, smoke dispersion and visibility are low. Conversely, unstable air masses promote quick smoke removal to the upper atmosphere.
• Relative humidity. Because air humidity correlates with moisture content in plants and affects their inflammation property, forest prescribed burns must not take place when air humidity is too high or too low. Fuels won’t burn sufficiently when the air is too humid and will ignite faster when they are too dry. Besides, wet vegetation produces a lot of smoke.
  
• Precipitation. Rainfalls support soil moisture, and the earth should be relatively wet to prevent root damage and undersurface organic matter ignition.

How Often Does Forestry Do Controlled Burning?

The interval may vary from one to fifty years. Typically, controlled forest fires are conducted every year, but a burn in a hardwood forest may be done even within shorter periods. The time frameworks between the prescribed events depend on the amount of fuel, vegetation time, climatic conditions, and topographic specifics.

Best Time To Do A Prescribed Burn In A Forest

Controlled forest burns usually take place in early spring before vegetation turns green – from February to mid-April or the middle of May. However, the time of the year depends on the purpose of controlled burning of forestland. Prescribed spring events help manage wildlife habitats or decrease combustive fuels. Prescribed summer events are necessary to release the seeds of fire-dependent species^{Chapter Introduction: Fire Ecology. blm.gov} (e.g., pines) that won’t drop until the cone resin melts.

As for timing during the day, the event must be completed before sunset. Start fire for a prescribed burn in the forest from 10 a.m. to noon.

Controlled Burning Benefits: Why Prescribed Fire Is Good

Controlled forest ignition is justified for various reasons, and the major benefits of prescribed fire on forests are as follows:

• induced reproduction of fire-dependent species;
• prepared forestlands for reforestation;
• reduced forest fires risks and intensity with a controlled burn;
• mitigated wildfire risks by eliminating flammable fuels;
• destroyed weeds to decrease competition, including parasitic plants^{Parasitic plants can amplify forest vulnerability to climate change. Pacific Northwest Research Station. US Forest Service. 2020};
• killed pests and pathogens to address tree diseases;
• favorable changes in forest cover after prescribed fire events;
• rejuvenated picturesque landscapes;
• released nutrients and improved soils;
• refreshed pastures for grazing.

Negative Effects Of Controlled Burning: Why Prescribed Fire Is Bad

Despite prescribed fires are generally beneficial to forest health, there are certain disadvantages of controlled burning:

• risks of flame escapes;
• health issues induced by smoke;
• released carbon dioxide from trees and forest soils;
• erosion and sedimentation due to a lack of soil cover;
• destroyed non-target plant species and wildlife.

Satellite Technologies To Assist In Prescribed Fires

Controlled ignition management is a challenging task due to potential risks and harm to people and nature. Because the right outcome of properly controlled events greatly depends on suitable meteorological conditions, accurate weather forecasts predetermine the prescribed fire success.

EOSDA Forest Monitoring is a helpful tool that provides the necessary data to support this need. Having at disposal reliable 14-day forecasts for selected AOIs, foresters and/or forest landowners can plan how to apply controlled burn to survive forest fires or improve vegetation health.

Weather prediction gets more complicated due to climate change. Nonetheless, EOSDA Forest Monitoring provides weather data archives, e.g., accumulated precipitation and temperature trends. Such information is useful to plan prescribed fires both in the nearest future and for years to come.

Temperature anomalies monitoring is another valuable feature on the platform. It allows for monitoring zones when the air temperature is extremely high (up to several hundred degrees). In most cases, such temperature leaps mean forest ignition. The areas with temperature anomalies are likely to indicate active or spreading fires.

This information is also very important while planning prescribed fire events as you can know if there are potentially dangerous areas on your AOI or near it. In case of a nearby spreading wildfire, you will be able to track its trajectory. By analyzing the forecasted wind direction and speed, it is possible to understand if your AOI is safe or if any prevention measures are needed.

EOSDA Forest Monitoring also includes other features to plan and do a prescribed burn, e.g. timely high-temperature alert system. You will get alerts once any sources of temperature anomalies are detected within the selected AOIs.
Besides, it is important to track the forest changes in order to understand if the expected results are gained. The platform helps analyze the area size before and after controlled burn events by historical and current NDVI index values.

More Prescribed Burns Mean Fewer Extreme Wildfires

When implemented with due precaution, controlled fire can do a lot of good. Apart from benefits for forest health, it is an effective practice to control and prevent forest ignition. By destroying combustible fuels in time, foresters mitigate the risks of potential wildfires by up to 72%^{Francisco Tutella. Fire operations-prescribed burning combo reduces wildfire severity up to 72%. Penn State University. 2021}, yet we should never forget why controlled burning is bad.

Proper situation management is possible with ongoing forestland observation, and EOSDA Forest Monitoring is a reliable assistant in this regard. Request a demo or learn more about our product features from the sales department at sales@eosda.com.