Prescribed Fire

Burned branch

Fire has been an integral part of Florida's natural environment for millennia. The peninsular shape of Florida places most of Florida within the influences of sea breezes; that combined with its subtropical climate makes thunderstorms a common summer occurrence. The thunderstorms in turn are ready producers of lightning, and this common fire starter has resulted in the adaptation of Florida's flora and fauna to adapt to frequent fires.

In fact, many of Florida's upland habitats are dependent upon fire to maintain their health and biodiversity. These include sandhills, pine flatwoods and shrubs, though other habitats such as prairie and saltmarsh also benefit from fire.

Fire serves a number of purposes in these habitats. First, it eliminates competitive vegetation that has not adapted to survive fires. Second, it converts fallen material such as branches, leaves, needles, and logs back into nutrients and minerals that the surviving plants can now easily absorb. It also clears out underbrush and opens the soil, thus allowing seeds to germinate and grow.

Finally, the vigorous regrowth of surviving plants and the stimulated germination of new seedlings provides a more nutritious food for the animals such as deer, gopher tortoises, and insects which feed on vegetation.

Native Americans recognized the value of fire and often utilized it to sustain desirable wildlife populations or edible plants. Early pioneers of Florida also recognized its value, but over time, as Florida's residents became less dependent on the local environment for survival, the use of fire as a habitat maintenance tool fell out of favor. In fact, recognition of fire as a tool changed to the perception that fire was an enemy to be suppressed whenever it occurred on natural lands.

The suppression of fire resulted in environmental changes both subtle and drastic. The lack of fire allowed fire-vulnerable vegetation (particularly oaks) to survive and in time dominate the former sandhill and pine flatwoods of Florida. The oaks because of their denser, light-blocking canopy and ground covering leaf litter reduced or eliminated the grasses, wildflowers, and forbs that once made up the bulk of the groundcover in fire-dependent habitat. This in turn changed the wildlife composition, and sandhill/flatwood species such as gopher tortoises, red cockaded woodpeckers, and kestrels declined in population.

Scrub Restoration Project sign

Equally important, the lack of fire allowed combustible fuels such as pine needles, branches, and downed trees to accumulate. Whereas naturally occurring, frequent wildfires burned quickly and low to the ground, when fire broke out in these suppressed areas the accumulated debris fueled fierce large fires, consuming both understory and overstory vegetation. The catastrophic fires of the East Coast of Florida in 1998 were an example of the devastation that can occur in a fire-dependent habitat when fire is excluded for long periods.

To restore these natural habitats and reduce the lands vulnerability to uncontrollable wildfires, Florida's public (and many private) land manager's have restored the use of fire as a habitat management tool. Today's land managers use prescribed fires on a frequent basis to maintain the health and biodiversity of many of our public lands.

Prescribed burning in Florida is regulated under Florida Statute 590.125. It defines "prescribed burning" as the controlled application of fire in accordance with a written prescription for vegetative fuels under specified environmental conditions while following appropriate precautionary measures that ensure that the fire is confined to a predetermined area to accomplish the planned fire or land-management objectives. It also establishes a definition for a certified prescribed burn manager with certification criteria being set by the Florida Division of Forestry. Citrus County is fortunate to have over 1/2 of its acreage in public ownership. Many of these sites are dedicated to conservation, and the use of prescribed fire is a necessary management tool. Sites such as the Withlacoochee State Forest, Crystal River State Park, Flying Eagle, Pott's Preserve, and Two-Mile Prairie are burned on a rotation of 3 to 5 years. Even smaller properties such as Fort Cooper State Park, The Homosassa Springs Wildlife State Park, and the Cross Florida Greenway use prescribed fire to restore habitats to their former natural state.

Newly acquired land such as the Annutliega Hammock and Lecanto Sandhill will require extensive prescribed burns and regular burn maintenance to bring them back to their natural state.

For this reason, the citizens of Citrus County must learn to recognize the value of prescribed burns and tolerate the occasional inconveniences associated with it. This webpage is created to better inform you of the actions, considerations, and factors that influence when, where, and what time prescribed burns are set.

Weather Influences

Woods

Wind, humidity, temperature, rainfall, and airmass stability are all-important considerations in prescribed burn scheduling. Winter is the common season for most burns because the winds are more consistent and stable, and humidity is low. One of the ideal periods is after the passage of a cold front, particularly if it brought rain.

Prescribed burns are held in other seasons as well, but Florida's weather is less predictable, so great caution is used by land managers. The timing of burns is critical as well, as the acreage, land condition, past and pending weather in making the decision to prescribe burn. Burns conducted in winter months are typically for fuel reduction, whereas burns conducted in the growing season mimics the more natural occurrence of fires during Florida’s dry/growing season.

Wind

The preferred windspeed for prescribed burns is 1 to 3 mph in-stand (measured at eye-level). However, windspeed to a height of 20 feet is also taken into consideration, particularly in open areas. The minimum 20-foot height windspeed for prescribed burning is 6 mph to a maximum of 20 mph. Higher windspeeds dissipate the heat of the burn, which reduces crown scorching.

Direction obviously guides the fire, but of even more importance is the duration of time that the wind blows in the same direction. This is why winter is a preferred prescribed burn season because past cold front winds are typically out of the west or northwest and can persist for several days. As the coldfront influence declines, the wind direction typically shifts clockwise, thus causing the fire to die naturally.

Relative Humidity

The amount of moisture in the air or humidity influences the intensity of a fire. Desired humidity typically is from 30 to 50%. Humidity below 30% presents potentially dangerous conditions because the fine fuel such as pine needles and grass respond readily to humidity levels. Humidity greater than 60% causes fires to burn incompletely leaving unburned islands within the target tract.

Temperature

Temperature is a major influence on fuel moisture content. Therefore, burns at temperatures of 60° or below are preferred. Instantaneous combustion for living tissue is around 145°, though the bark of large trees (particularly pine trees) provides additional protection. On occasions where the elimination of undesirable species such as encroaching hardwoods or invasive exotics is desired, burns with ambient temperatures as high as 90 to 95° are used.

Land Influences

The condition of the land to be burned must be carefully evaluated prior to conducting a burn. The land contours, habitat, road crossings, both paved and unpaved, water bodies, wildlife and the surrounding lands, both developed and undeveloped, all play roles in prescribed fire planning.

Habitat

Habitats that are fire dependent, i.e. those evolved to survive and thrive because of frequent burning, include sandhill, scrub, and pine flatwoods. Typically, the plants within these ecosystems share certain characteristics. These include storing the majority of their energy below ground in their roof system and protective measures such as thick bark of leaf bases that shied the living tissue from dire. They also produce litter that is readily combustible such as pine leaves, grass blades, and thin leaves. Another common trait is seed germination and seed dispersal that is often triggered by fire.

All Florida habitats are vulnerable to fire, and prescribed burns are a useful management tool within these areas as well. However, the plants within these habitats are not as readily adaptable to survive fires, so planning of these fires and the conditions they create (such as smoke) requires different approaches.

Land Contours

While Florida is viewed as flatland, it does have subtle rises and valleys that influence wind and vegetation growth. Water bodies such as creeks, ponds, and swamps also affect fire travel in speed and direction.

Road Crossings

Roads affect fire planning as well. First, since roads were created for transportation and smoke impedes visibility, careful planning must occur anytime prescribed burns are held near roadways. Internal dirt roads are usually closed or access limited, but that option is typically not available for paved public roadways. In these cases, education and precautionary actions such as signage or reducing speed are used.

Roads also influence vegetation (referred to as the edge effect) and can channel wind. In addition, since roads have minimal fuel for burning, they can serve as firebreaks, though fire (particularly with higher winds or fuel presence) can jump roads readily.

Animal Hole

Wildlife

Most wildlife can readily avoid fire either by staying ahead of the flames or taking shelter (holes, tree tops, dense thickets). However, nesting birds, young mammals, and amphibians can be vulnerable to fire, so these factors are also considered in the development of any prescribed burn plan.

Surrounding Property

Any prescribed burn has targeted boundaries, but the impacts of the fire (particularly smoke) extend well beyond the burn area boundaries. The greater the presence of development, the more limitations must be built into a burn plan. In some cases, these factors are so great that prescribed burning can no longer be used as a tool for land management.

In these cases more expensive management options must be utilized or in some cases the habitat is lost to succession as fire vulnerable hardwoods invade and dominate the area. This can lead to the loss or reduction of many critical species such as scrub jays, red cockaded woodpeckers and gopher tortoises.

For these reasons, careful land use planning must be exercised for property near public lands. Education also plays a critical role as Florida's population continues to grow.

Fuel Influence

Many fire-adapted species are also of high economic value. In particular, pine trees are a major component of the southern timber industry. The harvest of pine trees leaves behind pine tops and branches which will readily burn and burn for much longer periods than the normal needle litter.

Fuel also builds when fire is excluded from an area for extended periods. In addition to the accumulated leaf litter, fire-vulnerable species colonize the area, and this presence can allow fire to climb from the ground into the fire-vulnerable canopy of the otherwise resistant mature pines. Therefore, careful calculation of fuel volume is always involved in prescribed fire planning.

Firing Techniques

After all the influences have been identified and incorporated into the prescribed fire burn plan, the fire crew and burn manager have the ability to utilize various techniques to manipulate the progression of a burn. These include wind utilization, single or multiple burn points, circular firing and fire lane construction. A short description of the more common firing techniques is provided below:

  • Backing Fire – A fire spreading or set to spread into or against the wind or downhill.
  • Flanking Fire – A fire spreading or set to spread at right angles to the prevailing winds.
  • Heading Fire – A fire front spreading or set to spread with the wind or upslope.
  • Strip Heading Fire – A series of lines of fire upwind (or downslope) of a firebreak or backing fire that will burn with the wind toward the firebreak or backing fire.
  • Point Source Fires – A series of point fires often in a grid system to consume fuel ahead of the main fire line.
  • Aerial Ignition – The dropping of fire ignition devices to improve fire coverage or to introduce fires where natural or manmade obstacles inhibit fire’s ability to reach the area naturally.
  • Center and Circular (Ring) Firing – The establishment of a ring of fire starting with the downwind control line so the fire will converge around the center. This technique creates a hot fire and is typically used to eliminate logging debris or prepare a site for seeding.
  • Pile and Windrow Burning – Essentially a limited location fire intended to consume debris with a prolonged burn. Commonly used as a component of site development.

Smoke Management

Path

To most members of the public, the core of their interest in prescribed fire is smoke management. Smoke is an unavoidable component of prescribed fire, and it is often carried far from its point of origin. Like all smoke, prescribed fire smoke can trigger respiratory difficulties for people with certain medical conditions. In addition, it can obscure vision and create unsafe road conditions if thick or suppressed into pockets. Because of the transient nature of wind, smoke management is as much art as science, and even the most experienced burn manager can face unanticipated smoke dispersal when expected conditions do not appear or occur at the wrong time.

Smoke management guidelines have been developed utilizing ventilation rates and dispersal indexes. Smoke management systems all evolve around 5 steps:

  • Plotting the direction of the smoke plume
  • Identifying smoke sensitive areas
  • Identifying critical smoke sensitive areas
  • Determining the fuel type
  • Minimizing risk

Preparation for a Prescribed Burn

The first and foremost preparation for a Prescribed Burn is the careful and calculated development of a Prescribed Burning Plan. This plan is always in writing and is typically peer reviewed. Once the plan is developed and accepted, necessary pre-burn site work such as establishing control lines and plow lines is conducted. Pre-positioning of monitoring stations, public notification, mobilization or placing on call emergency crews for implementing burn modifications or safety teams (such as law enforcement to monitor roads) are all pre-arranged before a burn is started.

Executing a Burn

After everything listed above has occurred AND the desired conditions for a safe and productive prescribed burn are present, the burn boss authorizes the crews to begin. All involved in a prescribed burn are properly equipped, trained, and briefed on the burn plan and communication is a constant companion. The progress of the fire is monitored throughout the burn window and adjustments are made when necessary.

While the purpose of a prescribed burn is to aid management of the site being burned, the number one priority of any burn is Safety First.

Florida and Citrus County are very fortunate in having some of the most experienced Prescribed Burn specialists in the State. We also benefit from well-trained and equipped fire teams and strong intergovernmental coordination between local, state, and federal officials.

Evaluating a Burn

The work does not end with the completion of a prescribed burn. After a burn, the site is evaluated on a number of factors. These include completion of burn, consumption of fuel, crown scorch, post burn survival of desired species and effectiveness of smoke management planning. The information gathered from this evaluation becomes a part of prescribed burn databases that are utilized by burn managers and planners for future operations. The health and survival of our public lands is dependent on this important management tool.

Please remember the next time you hear or see a prescribed burn that the fire you are witnessing is the culmination of a carefully designed land management project that will help preserve Florida’s valuable natural resources.

This webpage was based on the National Wildlife Coordinating Group publication - A Guide for Prescribed Fire in Southern Forest (PMS 431-2/NFES 2108 - February 1989). It was developed in cooperation with and assistance from the dedicated public land managers of the Florida Division of Forestry, Florida Department of Environmental Protection, and Florida Fish and Wildlife Conservation Commission.

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