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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 regions, are large 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, however, in some ecosystems wildland fire is one of the major factors in determining community structure and composition.
Fire disturbance regimes can be characterized by:
See "Condition Class Attributes: Defining Fire Regimes" on page 11 for a discussion of the five fire regime groups.
The community structure and species composition at any given site are responses to various aspects of disturbance. Over time, disturbance regimes such as flood, drought, and fire have molded the composition, structure, and ecological processes of the world's ecosystems.
Organisms within these ecosystems have evolved to survive the disturbance regimes unique to an area. Species adaptations to disturbances can be thought of as the evolution of morphological 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 selective pressures, such as grazing or drought.
Many plants have evolved adaptations that protect them as a species from being extirpated by wildland fire, i.e., fire resistant adaptations. The most common example of fire protection is the thick bark on some species of trees in fire dominated ecosystems, such as ponderosa pine and bur oak. In addition, some species have protective coverings over critical plant parts; examples of these coverings are the needle and scale coverings over the buds on longleaf pine, and the below-ground meristem tissue (where growth occurs) in grasses.
Several adaptations relate plant growth to fire, i.e., growth-related adaptations. Some trees, such as ponderosa pine, actually increase their growth rate in the years following a fire; this response is visible in the annual rings in the cross section of trunks. Other growth-related adaptations include dormant buds that begin growing after limbs and branches are burned away, stimulation of suckering from the stumps of burned trees, and lignotubers (dormant below-ground buds in some legumes).
Several reproductive-oriented adaptations allow plants to take advantage of, or even require, wildland fire. Fire has been shown to trigger and/or increase seed release in some species, such as lodgepole and jack pines, and to stimulate flowering and fruiting in some shrubs and herbs. Some seeds remain dormant until the seedcoat is scarified, or cracked, which can result from intense heat or fire. Some pines have serotinous cones, in which the seeds are sealed in the cone by a waxy pitch that requires fire to remove the seals and free the seeds for germination.
Fire can also prepare seedbeds for germination by burning leaf litter. Some seeds require mineral soil for germination, and fire can release nutrients in the soil and make them available for sprouting plants. Likewise, fire can remove overstory plant material permitting sunlight to bathe the lower plant strata.
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. The immediate impact of wildland fire on animals is generally less intense, as both vertebrates and invertebrates have been shown to be fairly successful at avoiding being burned in fire. However, major changes in the plant communities following a fire have significant impacts on the animal communities that inhabit these ecosystems.
Over time, however, the impacts of human generated 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.
It is essential for communicators of wildland fire information to stress the importance of fire on the ecosystem health, and to inform audiences that wildland fire management practices used in one ecosystem will not necessarily benefit another. This section of the Guide provides a brief overview of seven fire-dependent ecosystems within the United States to illustrate how to frame stories when communicating with audiences about the role of fire.
Historically, tallgrass prairies covered parts of Nebraska, Illinois, Iowa, and Kansas. To the west, the tallgrass prairie graded into shortgrass prairie. To the east the tallgrass prairie included increasing numbers of trees, first as scattered oak savannahs and gallery forests, eventually becoming forests with prairie openings. These extended eastward into the Ohio Valley.
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 stress on the prairie ecosystem, and to make conditions more likely that fire will occur by drying potential fuels. 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 litter and preparation of the seedbed. In addition, perennials have greater seed production, germination, and establishment after a fire. The seeds of some forbs, such as prairie sunflower, scarify and leave dormancy following fire. Growth of native species such as big bluestem, little bluestem, and Indian grass all increase significantly following a fire. Fire promotes grasses at the expense of woody species; those woody species that do occur in savannahs are usually thick-barked species such as bur oak. Because of predominantly westerly winds across American prairies, trees are sometimes found on the eastern bank of streams and rivers that stop fires spread by these winds.
When fire is removed from a prairie ecosystem, woody shrubs and trees eventually replace grasses and forbs. Mowing is not a good replacement for fire in prairies because it does not reduce litter. Grazing is not a good replacement because it exerts a selective pressure on some grass species while leaving others untouched.
Almost exclusively, burning is prescribed for the restoration and maintenance of prairie reserves. In most managed prairies, prescribed fire is introduced on a two- to three-year cycle. The time of the year during which these fires are ignited is of primary importance. Plant recovery following a prairie fire is fastest in the spring and fall when soil moisture is high and plants are not producing seeds. If the area is burned when soil moisture is low, or when plants are starting to produce seeds, the recovery will take longer following the fire.
Chaparral is a general term that applies to various types of brushland found in Southern California, Arizona, New Mexico, and parts of the Rocky Mountains. True chaparral exists primarily in Southern California and describes areas that have a Mediterranean-like climate with hot, dry summers and mild, wet winters. The chaparral in this region is primarily fire-induced, and grows in soils that are shallow and unable to hold water. Generally, the terrain is steep and displays severe erosion. Variations in species cover throughout the area is attributed to the soil type and exposure, the altitude at which it grows, and the frequency of wildland fires.
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 community is dominated by annual grasses. Five years after a fire, chaparral shrubs once again dominate the ecosystem; for this reason, more frequent fires favor grasses over shrubs. Fire has not been successfully removed from this ecosystem, so how the community would respond to lack of fire is not well-known, although non-fire adapted trees and shrubs might replace the chamise, manzanita, and Ceanothus.
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 throughout the season. This ecosystem contains water-repellent soils, loose surface debris, and steep terrain, all adding to the high risk of unwanted wildland fire. Obstacles to using prescribed burning include the nearness of housing (urban-wildland interface) and the issue of smoke management. Burning also increases the amount of soil erosion, which is especially problematic in developed areas. Some work has been accomplished to replace the chaparral plant community with grasses, but this practice further threatens the existence of the species dependent on this ecosystem.
Ponderosa pine ecosystems occur as transitions between grasslands and deserts at lower elevations and higher level alpine communities. These ecosystems are found from the southwestern mountains as far north as Washington and Oregon, and east to the Dakotas, sometimes as nearly pure stands of ponderosa pine, and sometimes mixed with other species, such as Douglas fir. This forest community generally exists in areas with annual rainfall of 25 inches or less.
The characteristic surface cover in a ponderosa pine forest is a mix of grass, forbs, and shrubs. The natural fire regime has a cycle of five to 25 years, with moderate regularity. These fires tend to be low intensity ground fires that remove woody shrubs and favor grasses, creating open, park-like ponderosa stands.
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 groundfires.
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. Additionally, Douglas firs possess characteristics that enable them to withstand fire when it does occur. For example, this species is more resistant to fire than most other conifers. Additionally, the Douglas firs' abundantly produced seeds are lightweight and winged, allowing the wind to carry them to new locations where seedlings can be established. Douglas fir regenerates readily on sites that are prepared by fire. In fact, nearly all the natural stands of Douglas fir in the United States originated following fire. One of the main benefits of fire in these forest communities is the removal of fuel and consequent reduction of the chance of severe crown fires. Because Douglas fir exists in the presence of other types of trees, the life cycles of many species must be considered when timing a prescribed fire in this type of forest community.
Lodgepole pines are found throughout the Rocky Mountains of the western United States, generally in unmixed stands at higher elevations. Major fires occur at intervals of 200 to 300 years in this ecosystem, and these fire events are often high intensity crown fires that kill trees. Each successional stage of a lodgepole pine community displays different reactions to fire.
At 40 to 50 years following a stand-replacing fire, herbaceous plants and lodgepole seedlings grow between the snags and the logs that were damaged by the fire. The forest tends to resist fire at this stage, in that the only fuel 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 250Ä350 years old.
When fire does not occur, lodgepole pines are sometimes gradually replaced by Engleman spruce and subalpine fir, although the successional pathway is site dependent. Fire regimes in lodgepole pine communities can be very irregular, thus community dynamics are difficult to predict.
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, the results can be in vast acreages being burned, and 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 forests, consisting mainly of loblolly, shortleaf, or longleaf pines are found from Texas east to Florida, and north to Maryland. Various species of oaks are often present, especially when fire has not occurred recently. Shrubs can also be present, such as saw palmetto and bayberry; grasses are also common, such as little bluestem and wiregrass.
Lightning ignited fires in southern pine communities are common. More frequent fires favor longleaf pines, which are more fire adapted; less frequent fires tend to favor shortleaf and loblolly pines. Frequent fires also create pine savannahs when understory shrubs are burned away, favoring the establishment of grasses beneath the pines. In cases where fire does not occur for 25 years or more, such as when fire is removed from the system or on wet sites where fire seldom occurs, hardwoods such as oaks and hickories gradually replace the pines.
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.
A mixture of pines and other tree species is found in the forests of the Great Lake states. Red, white, and jack pine grow among paper birch and aspen. Grasses, forbs, and shrubs such as big bluestem, little bluestem, raspberry, blueberry, and huckleberry grow under the trees of these communities. The communities of the Great Lakes states have suffered many disturbances since European settlement, making it difficult to determine the "natural" state of these ecosystems.
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 is a vast landscape covered with boreal forest and tundra, all prone to wildland fire. The boreal forest is found in southern Alaska extending as far north as Fairbanks. Tundra is found in the higher elevation of this zone. Tundra extends from the Brooks Range north to the Arctic Ocean.
While the boreal forest has large vegetation (e.g., spruce and birch trees) and nutrient-ladened 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 mass 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 regimes.
Wildland fire occurs naturally and plays varying roles in nearly all terrestrial ecosystems. Because different types of ecosystems produce and accumulate fuel more quickly than others, the wildland fire frequency and intensity are determined by the type and the stage of development of the ecosystem in which it occurs. Depending on the fire regime, many species evolve adaptation to fire, making fire important for competition with other species, or even necessary for reproduction. Fire, in a natural or prescribed form, is important to the maintenance and health of most ecosystems.
Archibold, O.W. 1995. Ecology of World Vegetation. London; New York: Chapman & Hall.
Pyne, S.J., P.L. Andrews, and R.D. Laven. 1996. Introduction to Wildland Fire, 2nd Edition. New York: John Wiley & Sons, Inc.
Author: K. Jeffrey Danter