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Aerial Fuels: All live and dead vegetation in the forest canopy or above surface fuels, including tree branches, twigs and cones, snags, moss, and high brush.
 
Backfire: A fire set along the inner edge of a fireline to consume the fuel in the path of a wildfire and/or change the direction of force of the fire’s convection column.
 
Brush: A collective term that refers to stands of vegetation dominated by shrubby, woody plants, or low growing trees, usually of a type undesirable for livestock or timber management.
 
Brush Fire: A fire burning in vegetation that is predominantly shrubs, brush and scrub growth.
 
Buffer Zones: An area of reduced vegetation that separates wildlands from vulnerable residential or business developments. This barrier is similar to a greenbelt in that it is usually used for another purpose such as agriculture, recreation areas, parks, or golf courses.

Conduction: Moves heat from one fuel particle to the next (heat transfer between solid objects), like when the stove burner heats a pan and its contents.
 
Contain a fire: A fuel break around the fire has been completed. This break may include natural barriers or manually and/or mechanically constructed line.
 
Control a fire: The complete extinguishment of a fire, including spot fires. Fireline has been strengthened so that flare-ups from within the perimeter of the fire will not break through this line.
 
Control Line: All built or natural fire barriers and treated fire edge used to control a fire.
 
Convection: The transfer of heat through the flow of liquids or gases, such as when hot air rises through a chimney.  Convection currents are often responsible for the pre-heating of higher shrub layers and tree canopies, thus carrying the fire upward.

Conversion Burning: Takes place when one vegetative community on a site is replaced by another because of fire.

Creeping Fire: Fire burning with a low flame and spreading slowly.
 
Crown Fire (Crowning): The movement of fire through the crowns of trees or shrubs more or less independently of the surface fire.
 
Curing: Drying and browning of herbaceous vegetation or slash.
 
Dead Fuels: Fuels with no living tissue in which moisture content is governed almost entirely by atmospheric moisture (relative humidity and precipitation), dry-bulb temperature, and solar radiation.
 
Defensible Space: An area either natural or manmade where material capable of causing a fire to spread has been treated, cleared, reduced, or changed to act as a barrier between an advancing wildland fire and the loss to life, property, or resources. In practice, "defensible space" is defined as an area a minimum of 30 feet around a structure that is cleared of flammable brush or vegetation.
 
Duff: The layer of decomposing organic materials lying below the litter layer of freshly fallen twigs, needles, and leaves and immediately above the mineral soil.

Extreme Fire Behavior: "Extreme" implies a level of fire behavior characteristics that ordinarily precludes methods of direct control action. One of more of the following is usually involved: high rate of spread, prolific crowning and/or spotting, presence of fire whirls, strong convection column. Predictability is difficult because such fires often exercise some degree of influence on their environment and behave erratically, sometimes dangerously.

Fine (Light) Fuels: Fast-drying fuels, generally with a comparatively high surface area-to-volume ratio, which are less than 1/4-inch in diameter and have a timelag of one hour or less. These fuels readily ignite and are rapidly consumed by fire when dry.
 
Fingers of a Fire: The long narrow extensions of a fire projecting from the main body.


 

Fire: Manifestation of a series of chemical reactions.  Rapid release of the heat stored in (living and dead) plants by photosynthesis.

Fire Adaptation: When species have evolved with special traits contributing to successful abilities to survive fires (ex. serotinous cones, fire resistant bark)

Fire Behavior: The manner in which a fire reacts to the influences of fuel, weather and topography.
 
Fire Break: A natural or constructed barrier used to stop or check fires that may occur, or to provide a control line from which to work.

Fire Cycle: Length of time for an area equal to the entire area of interest to burn; size of the area of interest must be clearly specified.

Fire Dependence: A concept that applies to species of plants that rely on the effects of fire to make the environment more hospitable for their regeneration and growth.


Fire Duration: The length of time that combustion occurs at a given point. Fire duration relates closely to downward heating and fire effects below the fuel surface as well as heating of tree boles above the surface.


Fire Ecology: A branch of ecology that studies the relationship of fire with living organisms and their environment.


Fire Exclusion: The policy of suppressing all wildland fires in an area.


Fire Frequency = Fire Occurrence: Number of fires per unit time in a specified area.


Fire History: A concept that describes how often fires occur in a geographical area.


Fire Intensity: A general term relating to the heat energy released by a fire.


Fire Interval: Time (in years) between two successive fires in a designated area (i.e., the interval between two successive fire occurrences); the size of the area must be clearly specified.


Fire Management: Refers to all the management activities required for the protection of burnable valuables from fire and for the use of fire to meet specified management goals and objectives.

Fire Perimeter: The entire outer edge or boundary of a fire.


Fire Regime: Describes the patterns of fire occurrence, size, and severity - and sometimes, vegetation and fire effects as well - in a given area or ecosystem. A fire regime is a generalization based on fire histories at individual sites. 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.


Fire-Resistant Species: Species with morphological characteristics that give it a lower probability of being injured or killed by fire than a FIRE-SENSITIVE species, which has a "relatively high" probability of being injured or killed by fire.


Fire Severity: Degree to which a site has been altered or disrupted by fire; also used to describe the product of fire intensity and residence time.


Fire Storm: Violent convection caused by a large continuous area of intense fire. Often characterized by destructively violent surface indrafts, near and beyond the perimeter, and sometimes by tornado-like whirls.

Fire Triangle: Instructional aid in which the sides of a triangle are used to represent the three factors (oxygen, heat, fuel) necessary for combustion and flame production; removal of any of the three factors causes flame production to cease.

Fire Whirl: Spinning vortex column of ascending hot air and gases rising from a fire and carrying aloft smoke, debris, and flame. Fire whirls range in size from less than one foot to more than 500 feet in diameter. Large fire whirls have the intensity of a small tornado.


Flammability: Relative ease with which a substance ignites and sustains combustion.


Flame: Gas-phase phenomenon of fire.


Flame Height: The average maximum vertical extension of flames at the leading edge of the fire front. Occasional flashes that rise above the general level of flames are not considered. This distance is less than the flame length if flames are tilted due to wind or slope.

Flame Length: The distance between the flame tip and the midpoint of the flame depth at the base of the flame (generally the ground surface); an indicator of fire intensity.

Flare-up: Any sudden acceleration of fire spread or intensification of a fire. Unlike a blow-up, a flare-up lasts a relatively short time and does not radically change control plans.

Flash Fuels: Fuels such as grass, leaves, draped pine needles, fern, tree moss and some kinds of slash, that ignite readily and are consumed rapidly when dry. Also called fine fuels.

Fuel: Combustible material. Includes, vegetation, such as grass, leaves, ground litter, plants, shrubs and trees, that feed a fire. (See Surface Fuels.)

Fuel Bed: An array of fuels usually constructed with specific loading, depth and particle size to meet experimental requirements; also, commonly used to describe the fuel composition in natural settings.

Fuel Continuity: A qualitative description of the distribution of fuel both horizontally and vertically. Continuous fuels readily support fire spread. The larger the fuel discontinuity, the greater the fire intensity required for fire spread.


Fuel Loading: The amount of fuel present expressed quantitatively in terms of weight of fuel per unit area.

Fuel Moisture: Percent or fraction of oven dry weight of fuel. It is the most important fuel property controlling flammability. In living plants it is physiologically bound. Its daily fluctuations vary considerably by species but are usually above 80 to 100%. As plants mature, moisture content decreases. When herbaceous plants cure, their moisture content responds as dead fuel moisture content, which fluctuates according to changes in temperature, humidity, and precipitation.


Fuel Reduction: Manipulation, including combustion, or removal of fuels to reduce the likelihood of ignition and/or to lessen potential damage and resistance to control.

Fuel Type: An identifiable association of fuel elements of a distinctive plant species, form, size, arrangement, or other characteristics that will cause a predictable rate of fire spread or difficulty of control under specified weather conditions.

Ground Fire: Fire that burns in the organic material below the litter layer, mostly by smoldering combustion. Fires in duff, peat, dead moss and lichens, and punky wood are typically ground fires.


Ground Fuel: All combustible materials below the surface litter, including duff, tree or shrub roots, punchy wood, peat, and sawdust, that normally support a glowing combustion without flame.

Head Fire: A fire spreading or set to spread with the wind.


Head of a Fire: The side of the fire having the fastest rate of spread.

Heavy Fuels: Fuels of large diameter such as snags, logs, large limb wood, that ignite and are consumed more slowly than flash fuels.

Ladder Fuels:
Fuels which provide vertical continuity between strata, thereby allowing fire to carry from surface fuels into the crowns of trees or shrubs with relative ease. They help initiate and assure the continuation of crowning.

Large Fire: 1) For statistical purposes, a fire burning more than a specified area of land e.g., 300 acres. 2) A fire burning with a size and intensity such that its behavior is determined by interaction between its own convection column and weather conditions above the surface.

Light (Fine) Fuels: Fast-drying fuels, generally with a comparatively high surface area-to-volume ratio, which are less than 1/4-inch in diameter and have a timelag of one hour or less. These fuels readily ignite and are rapidly consumed by fire when dry.

Litter: Top layer of the forest, scrubland, or grassland floor, directly above the fermentation layer, composed of loose debris of dead sticks, branches, twigs, and recently fallen leaves or needles, little altered in structure by decomposition.

Live Fuels: Living plants, such as trees, grasses, and shrubs, in which the seasonal moisture content cycle is controlled largely by internal physiological mechanisms, rather than by external weather influences.

Mean Fire Interval: Arithmetic average of all FIRE INTERVALS determined, in years, for a designated area during a specified time period; the size of the area and the time period must be specified.


Mixed-Severity Fire Regime: Fire regime in which fires either cause selective mortality in dominant vegetation, depending on different species’ susceptibility to fire, or vary between understory and stand replacement.


Mineral Soil: Soil layers below the predominantly organic horizons; soil with little combustible material.

Peak Fire Season: That period of the fire season during which fires are expected to ignite most readily, to burn with greater than average intensity, and to create damages at an unacceptable level.

Prescribed Fire:
Any fire ignited by management actions under certain, predetermined conditions to meet specific objectives related to hazardous fuels or habitat improvement. A written, approved prescribed fire plan must exist, and NEPA requirements must be met, prior to ignition.

Prescription: Measurable criteria that define conditions under which a prescribed fire may be ignited, guide selection of appropriate management responses, and indicate other required actions. Prescription criteria may include safety, economic, public health, environmental, geographic, administrative, social, or legal considerations.

Presettlement Fire Regime:
The time from about 1500 to the mid- to late-1800s, a period when Native American populations had already been heavily impacted by European presence and before extensive settlement by European Americans in most parts of North America, before extensive conversion of wildlands for agricultural and other purposes, and before fires were effectively suppressed in many areas.


Prevention: Activities directed at reducing the incidence of fires, including public education, law enforcement, personal contact, and reduction of fuel hazards.


Radiation: Transmits heat by rays, such as from the sun or a flame. Radiation accounts for most of the preheating of fuels surrounding a fire, allowing the fire to spread.

Serotinous: Pertaining to fruit or cones that remain on a tree without opening for 1 or more years. In some species (e.g., lodgepole pine), cones open and seeds are shed when heat is provided by fire or hot, dry conditions.


Slash: Debris left after logging, pruning, thinning or brush cutting; includes logs, chips, bark, branches, stumps and broken understory trees or brush.

Smoldering Fire: A fire burning without flame and barely spreading.

Snag: A standing dead tree or part of a dead tree from which at least the smaller branches have fallen.

Spot Fire: A fire ignited outside the perimeter of the main fire by flying sparks or embers.

Stand-Replacement Fire Regime: Fire regime in which fires kill or top-kill aboveground parts of the dominant vegetation, changing the aboveground structure substantially. Approximately 80% or more of the aboveground, dominant vegetation is either consumed or dies as a result of fires. Applies to forests, shrublands, and grasslands.


Succession: The gradual, somewhat predictable process of community change and replacement leading toward a climax community; the process of continuous colonization and extinction of populations at a particular site.


Surface Fire: Fire that burns in litter and other live and dead fuels at or near the surface of the ground, mostly by flaming combustion.


Surface Fire Regime: Fire regime in which fires are generally not lethal to the dominant vegetation and do not substantially change the structure of the dominant vegetation. Approximately 80% or more of the aboveground dominant vegetation survives fires. Applies to forest and woodland vegetation types.


Surface Fuels: Loose surface litter on the soil surface, normally consisting of fallen leaves or needles, twigs, bark, cones, and small branches that have not yet decayed enough to lose their identity; also grasses, forbs, low and medium shrubs, tree seedlings, heavier branchwood, downed logs, and stumps interspersed with or partially replacing the litter.

Top-Kill: Kills aboveground tissues of plant without killing underground parts from which the plant can produce new stems and leaves.


Total Heat Release:
The heat released by combustion during burnout of all fuels, expressed in BTU per square foot or kilocalories per square meter.


Wildland Fire: Any nonstructure fire, other than prescribed fire, that occurs in the wildland.

Wildland Urban Interface: The line, area or zone where structures and other human development meet or intermingle with undeveloped wildland or vegetative fuels.

Sources:

DeBano, L.F., Neary, D.G., & Ffolliot, P.F. (1998). Fire effects on ecosystems. New York: Wiley.

National Interagency Fire Center (2004). Glossary of wildland fire terms. Retrieved October 15, 2004 from http://www.nifc.gov/fireinfo/glossary.html

National Geographic Society. (2005). Wildworld glossary. Retrieved January 5, 2005 from http://www.nationalgeographic.com/wildworld/glossary.html

National Interagency Fire Center. (2005). Communicator’s guide: Wildland fire. Retrieved January 5, 2005 from http://www.nifc.gov/preved/comm_guide/wildfire/index2.html

U.S. Department of Agriculture, Forest Service. (2005). Fire effects information system glossary. Retrieved January  4, 2005 from http://www.fs.fed.us/database/feis/glossary.html

Western Fire ecology Center. (2005). Introduction to fire ecology. Retrieved January 5, 2005 from http://www.fire-ecology.org/education/doc1.htm

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Copyright 2004 San Diego State University Foundation