|2. Wildland Fire Overview|
This chapter outlines the
communicators should know
about wildland fire in order
to effectively communicate
this complex topic to various
audiences. A concise section
on the science of wildland
fire and its role in
ecosystems is included as
background information. You
can craft meaningful
Wildland fire is any non-structure fire that occurs in an area in which development is essentially non-existent, except for roads, railroads, power lines, and similar transportation facilities. Three distinct types of wildland fire have been defined by the National Wildfire Coordinating Group (NWCG):
When communicating about wildland fire management issues, it is important to be aware of the
Depending on the expertise of the audience, you may choose to limit the discussion to a simple overview of the fire triangle, or expand the discussion to include the technical details of flame structure and fuel chemistry. This section is intended to provide you with an overview of the scientific processes occurring with wildland fires.
The Fire Triangle
Three mechanisms of heat transfer exist: convection, radiation, and conduction. All three contribute in different ways to the combustion process, depending in part on the fuel distribution, the wind speed at the fire site, and the slope of the terrain.
Fuels char at relatively low temperatures, but once charred can continue to burn by glowing combustion. As fire spreads, there is constant ignition of new fuels through one of the three heat transfer mechanisms described earlier, and the fire continues to advance.
During the day, sunlight heats the ground and the warm air rises, allowing air currents to travel up sloped landscapes. At nightfall, the process is reversed. The ground cools and the air currents now travel down the slopes. Often fires will burn upslope during the day and down slope at night. Temperature acts upon the spread of wildland fires because the temperature of the fuel affects how quickly or slowly they will reach their ignition point and burn. Because fuels are also heated by solar radiation, fires in the shade will not burn as quickly as those in the direct path of sunlight.
Humidity is a measure of the amount of moisture in the air. This moisture dampens the fuel, slowing the spread of flames. Because humidity is greater at night, fires will often burn less intensely at that time under normal circumstances, and therefore will not travel a great distance.
The combination of wind, temperature, and humidity affects how fast wildland fires can spread. These combinations will change throughout the day and night, and the presence of fire will impact each factor, causing even greater variation.
An explanation of topography includes the shape of the landscape, its elevation, the slope direction and its exposure to sunlight, and the slope steepness (aspect).
The Complexity of the Fire Message
Wildland fire, as it moves, involves a changing situation. Fire itself changes its own environment,
Wildland fire is a natural process, and many ecosystems depend upon it. As we tell the story of fire to illustrate the science of wildland fire management, we also need to tell stories that promote coexistence with wildland fire. In discussing and addressing fire as a conservation issue, it is important to recognize and understand the different roles that fire plays in different ecosystems. The broad ecosystem categories of vegetation responses to fire below can be helpful in communicating general concepts to the public.
It is important for you and your audience to understand that fire regimes, like the entire natural world, are diverse and particular to their specific sites. Fire helps determine where different types of habitats exist around the world. Plants and animals have developed different responses to fire, with some dependent on fire and others sensitive to fire.
A fire regime is a set of recurring conditions of fire that characterizes a given ecosystem. The combination of fire frequency, intensity, severity, seasonality, size of burn, fire spread pattern, and pattern and distribution of burn circumscribe those conditions. Fire regimes can often be described as cycles because some parts of the histories usually get repeated, and the repetitions can be counted and measured, such as fire return interval.
An ecologically appropriate fire regime is one that maintains the viability of the ecosystem. An altered or undesirable fire regime is one that has been modified by human activities to the extent that the current fire regime negatively affects the viability of desired ecosystems and the sustainability of products and services that the ecosystem provides.
Although fire is one of the most important natural disturbances in many of the Earth's ecosystems, inevitably, conservation practitioners addressing fire issues find that they must also deal with other threats or issues that, because they affect fuels, alter fire regimes. We cannot effectively restore ecologically acceptable regimes unless we also understand and address the underlying causes of alteration. Some general sources are listed below; however, you may have a source unique to your particular area that you need to communicate to your audience.
Fire Regime Condition Class
Condition class attributes is an approach to defining and interpreting the importance of fire frequency in ecosystems. This concept is useful in helping wildland fire communicators convey to their audiences the science and management behind wildland fire.
Current "condition class" is defined in terms of departure from the historic fire regime, as determined
Three "condition classes" have been developed to categorize the current condition with respect to each of the five historic Fire Regime Groups.
A complete definition, background information, and the nationally consistent methodology for calculating and mapping FRCC are available at www.frcc.gov.
Map generated from LANDFIRE Rapid Assessment data.
A central tenet for communicators is "relate to your audience." Historically, most terrestrial ecosystems in the United States were dependent to some extent upon fire. Addressing wildland fire using local examples has the potential to better help people relate. Seven major ecosystems are used as examples of how to concisely frame local descriptions.
Ecosystems, or ecological communities, are geographic areas
containing similar biological communities and abiotic conditions,
such as temperature, rainfall, and seasons. They are tied through
flows of energy. These ecosystems are often identified by the
dominant plant communities found in the region. The plant species
found in these biological regions are a function of many factors,
including climate, interactions among species, and disturbance
regimes such as fire. Fire occurs in nearly all terrestrial ecosystems,
Fire disturbance regimes can be characterized by the following:
The community structure and species composition at any given site are responses to various aspects
Organisms within these ecosystems have evolved to survive the disturbance patterns unique to an
area. Species adaptations to disturbances can be thought of as the evolution of physical and
behavioral traits which allow for reproduction and the continuance of a species. Many plant species
have important adaptations that allow them to survive, thrive, and even require fire for survival.
However, it is important to recognize that not all adaptations that protect plants are a response to
fire, but may be a response to other pressures, such as grazing or drought. Following is a summary
of plant species adaptations to fire.
These adaptations, in combination with the local fire regime at a specific site, play an important role in determining the composition of the plant community.
Impact on Animals
Over time, however, the impacts of human generated fire or suppression of fire can have major consequences for animals. For example, the movement of American bison to the eastern United States in the 1500s may have resulted from Native Americans burning in the east which opened more grazing for bison. Recent studies of ancient Aboriginal "fire-stick farming" practices in Australia beginning 50,000 years ago suggest fire impacts as the reason for extinction of certain large animals.
Overview of Fire Dependent Ecosystems
Midwest Tallgrass Prairie
Tallgrass prairie is primarily made up of grasses and forbs, with some shrubs and trees. Prairie plant communities are a result of fire and drought, although some community structure is in part from grazing by bison and elk. Drought acts both as a direct and indirect stress on the prairie ecosystem because it dries potential fuels and increases the chances that fire will occur. In pre-Colombian times, natural fire sources were primarily from lightning strikes, although there is evidence that deliberate fires started by Native Americans were also common. Fires in the prairie usually occurred in five- to ten-year cycles, with moderate regularity. Fire in tallgrass prairies acts to burn above-ground biomass, killing woody plants, allowing sunlight to reach the soil, and changing the soil pH and nutrient availability. Grassland fires can cover large areas in a short time as fire fronts are driven by prairie winds. However, because grass provides a low quality of fuel, grassland fires usually are not intense.
Productivity usually increases following a fire in the prairie. Growth is stimulated by the removal of
When fire is removed from a prairie ecosystem, woody shrubs and trees eventually replace grasses
Almost exclusively, burning is prescribed for the restoration and maintenance of prairie reserves. In
Southwestern California Chaparral
Chamise (greasewood) is a common plant in this ecosystem. Other important shrubs include manzanitas, Ceanothus, and scrub oaks. Natural fires occur in 15- to 25-year cycles, with high regularity. Plant growth in southern California chaparral occurs during the wet winter months. This vegetation dries during the dry summer months when winds blow from the inland deserts toward the Pacific Ocean. Fires usually occur during the late summer Santa Ana winds, which are strong (up to 60 mph) and dry. These winds tend to drive fire rapidly through the dry brush.
Plants in this ecosystem are adapted to the Mediterranean climate, local soils, and the fire regime.
Fire adaptations include vigorous stump sprouting after fires by many shrubs, including the
manzanitas, Ceanothus, and scrub oak. Chamise produces dormant seeds that require fire for
scarification; these seeds create a large seed bank during non-fire years. In addition, most chaparral
plants seed quickly, usually within three to five years after sprouting. Many of the shrubs, especially
chamise, promote fire by producing highly flammable dead branches after about 20 years. Another
chaparral plant, Ceanothus, has leaves that are coated with flammable resins. Fires occurring at
intervals greater than 20 years are often high intensity because of the large amount of fuel existing in shrub tops. Many nutrients are locked in the foliage of chaparral plants. Through burning, these
nutrients are recycled back into the soil.
After fires in chaparral, forbs are usually profuse on the newly opened floor. After a year, the plant
Wildland fire control in the southern California chaparral ecosystem is very difficult because of the
existence of Santa Ana winds, the length of the summer season, and the heat and dryness present
Ponderosa Pine in the Southwest and Intermountain West
The characteristic surface cover in a ponderosa pine forest is a mix of grass, forbs, and shrubs. The
The life history of ponderosa pine is well adapted to high frequency, low intensity fires. These fires
burn litter and release soil nutrients, thus providing a good seedbed for ponderosa pine seeds. For
the first five years of their life cycle, ponderosa pine seedlings vigorously compete with grasses for
survival and are vulnerable to fire. Eventually, at about five or six years of age, the tree begins to
develop thick bark and deep roots and shed lower limbs. These factors increase its ability to
withstand fire and decrease the possibility of a fire climbing to the crown; crown fires can kill
ponderosa pines. Ponderosa needles on the ground facilitate the spread of low intensity ground fires
and reduce grasses that can intensify ground fires.
In ponderosa pine stands, fire is generally prescribed on five- to ten-year intervals to reduce fuel loads. Shorter burn intervals have insufficient fuel built up to maintain the fire, and longer periods may run the risk of causing tree-killing crown fires. Prescribed fires usually result in maintenance of stand composition.
Douglas fir is commonly found in association with ponderosa pine, but is able to survive without fire.
Lodgepole Pine Communities of the Rocky Mountains
At 40 to 50 years following a stand-replacing fire, herbaceous plants and lodgepole seedlings grow between snags and logs that were damaged by the fire. The forest tends to resist fire at this stage, in that the only fuels available are large logs that do not readily burn. From the age of 50 to 150 years, seedlings grow to a height of 50 feet, and the stands become so dense that little sunlight reaches the forest floor, therefore suppressing the growth of the understory. The sparseness of undergrowth also discourages the possibility of wildfire.
It is during the next successional stage of 150 to 300 years that the threat of wildland fire increases. Because of overcrowding, some of the lodgepole pines begin to die, which allows sunlight through, spurring vegetative growth. After 300 years, the original lodgepole pines die, making the forest highly susceptible to wildland fire. For example, the lodgepole pine stands in the Yellowstone area during the 1988 fires were 250–350 years old.
When fire does not occur, lodgepole pines are sometimes gradually replaced by Engleman spruce and
Wildland fire management in lodgepole pine communities can be problematic. Because there tend to be high intensity crown fires, allowing lightning ignited fires to burn can result in fires which are difficult to contain within management units. Prescribed fire is difficult to manage for the same reasons, and can endanger nearby human communities. Fire suppression, however, creates a fuel buildup that is difficult to manage, and suppression is not consistent with maintaining ecological communities.
Southern Pine Communities
Like many fire-adapted trees, longleaf pine requires mineral soil for seed germination, and thus ground fires prepare the seedbed by removing litter and releasing soil nutrients. The longleaf seedling grows slowly in the early years, devoting much energy to developing a thick root that is protected from fire, and to a dense protective layer of needles around the buds. Loblolly and shortleaf pines are less fire tolerant than longleaf pine, but the thick barks of these species also make them more fire tolerant than most other competitive tree species.
Jack Pine Communities of the Great Lakes Region
Jack pines are small trees, rarely exceeding 80 feet (about 24 meters) in height. They occur in poor soils, usually in open "pine barrens," and often form savannahs when grasses are present on the thin soils. Fires occur in jack pine stands approximately every 125 to 180 years. Jack pine is well-adapted to fire. Serotinous cones, which have a waxy outer coating to protect the seeds, remain on the tree rather than dropping to the forest floor. Seeds can remain viable on the tree for 20 years or longer. When a fire occurs, the thick cone protects the jack pine seed from the intense heat. Jack pine seeds have been known to still be viable after exposure to heat at 1000 degrees Fahrenheit. That heat, however, opens the scales of the cone and releases the seed onto the ground where the fire has removed much of the existing vegetation and litter. Jack pine seeds require contact with mineral soil to germinate, so fire serves to prepare the seedbed, reduce competition from other plants, and release the jack pine seed. In addition, the short stature of jack pines makes crown fires a high likelihood; these very crown fires are necessary to release the seeds from dormancy.
When fire is withheld from jack pine stands, they are replaced by other boreal tree species, such as balsam fir, white spruce, and the hardwoods that occur in this ecosystem. Prescribed fire is used in jack pine stands in central Michigan in order to maintain habitat for the rare Kirtland's warbler, which requires young jack pine stands for nesting.
Alaska's Boreal Forest and Tundra
While the boreal forest has large vegetation (e.g., spruce and birch trees) and nutrient-laden soil, the tundra is a low landscape comprised of scrubby and herbaceous vegetation, often only a few inches high. Much of the tundra soil and its nutrients are locked in permafrost. Often the soil is shallow; in some places it is no deeper than the shallow root structure of the tundra vegetation.
On the south-facing slopes of the boreal forest are spruce, birch, and aspen. North-facing slopes contain mostly black spruce and birch. Both of these slopes exhibit a unique succession; the successional stages are greatly impacted by wildland fire.
Following a fire, cottongrass, fireweed, and other herbaceous plants invade. Shrubs and berries move in after a few years only to be replaced by more mature trees such as willow, aspen, and birch. Eventually the spruce gets established and dominates, usually until the next fire. The heavy accumulation of litter makes these forests most susceptible to fire.
Fires in the boreal forest and tundra typically burn in a patchwork, leaving a mosaic across the landscape. Time of year, moisture present, wind speed and direction at the time of the fire, and biomass accumulation since the last fire, etc., all add to the rendering of the mosaic.
Because of Alaska's cool year-round temperatures, vegetation decays at a very slow rate, thereby releasing nutrients at a very slow rate. Following a fire in the boreal forest or tundra, large amounts of nutrients are released. Plants exploit this opportunity, especially the early successional plants. In turn, wildlife exploit the lush growth. Consequently, Alaska's plant and animal communities are highly dependent on fire.
Atlantic Coastal Pine Barrens
Rainfall averages about 48 inches per year, but the soil is sandy, extremely porous, and drains very
Historically, fire is the major disturbance factor influencing vegetation composition in the ecoregion. In its natural state, the landscape is swept by frequent fires, giving the advantage to species able to survive, such as pitch pine, scrub oak, heath shrubs, and bracken fern.
Eastern Deciduous Forests (Source: www.nearctica.com)
The Eastern Deciduous Forest is defined by the dominance of deciduous trees in the ecosystem.
Deciduous trees are almost all angiosperms such as oaks, maples, beech, hickories, and birches that
The Eastern Deciduous Forest develops under a particular set of climatic conditions. Winters are cold,
The species composition of the Eastern Deciduous Forest has changed over time. From 3,500 to 1,500 years ago, oaks were the dominate species. As the amount of burning increased from 1,500 to 240 years ago, chestnuts became the dominate species. In the past 200 years, the amount of burning has decreased and oaks again are becoming the dominate species.
None of the previously described ecosystems exist as a blanket across the areas specified in their description. This is particularly true of the Eastern Deciduous Forest. Notice, for instance, that the Southern Pine Communities occur within much of the same geographic range as the Eastern Deciduous Forest. This area includes many different combinations of climate and geology from the central lowlands below the Great Lakes, across the Appalachian Mountains, and onto the coastal plain. One result is a general transition, from North to South, of species like beech and maple to more oak and pine, and, generally, more fire-adapted systems with progressively shorter fire return intervals. In the coastal plain, where much of the Southern Pine Community exists, evergreen species, including hardwoods, become much more common as well. Another aspect of this region's diversity, especially in the Appalachians, is a mixture of different communities on different slopes and elevations. As a result, fire-adapted oak and pine communities occupy some areas, while mixed hardwoods and fire-sensitive conifers occur on sites which burn less frequently.
The definition of Fire Effects is the physical, biological, and ecological impacts of fire on the
environment. Both individual species and an integration of species and ecosystem responses to fire
are influences by fire season, fire behavior and characteristics, fuels, air quality, soils and watershed
plants, and wildlife. Variation in fire effects may occur within ecosystems because of differences in
site characteristics, fuel conditions, and weather prior to, during, and after fire. A fire may have
different effects upon the same site if it occurs in different seasons or within the same season but
different fuel. Fires affect animals mainly through effects on their habitat, which can be either
beneficial or harmful.
In addition, cultural resources including artifacts, structures, and
traditionally significant gathering places from both prehistoric and
historic eras can also be affected by wildfire. Therefore, you may
Understanding fire regimes, fire behavior and fire effects, and the differing needs of multiple species must be communicated to your audiences. Resource materials are available to guide you in developing messages on the ecological, physical and cultural impacts of fire:
Department of Agriculture, Forest Service, Rocky Mountain Research Station "Rainbow Series" on Effects of Wildland Fire on Ecosystems. This five-volume series covers air, soil and water, fauna, flora and fuels, and cultural resources (RMRS-GTR-42): www.fs.fed.us/rm/publications/.
National Wildlife Coordinating Group's (NWCG) publication Fire
Effects Guide (NFES #2394):