Appendix B - Glossary of Terms Used in Wildfire Management

Ad valorem:: according to the current value, e.g. an ad valorem tax on goods.
Annual grass treatment:: This treatment involves either chemical or mechanical methods for reducing flashy fuels associated with annual grass infestations (cheatgrass). Casarone® or other pre-emergent herbicides can be applied at the proper rates near residential areas to reduce the fuel load from annual grasses. Mowing the annual grasses once they dry-out in the spring, preferably before going to seed, reduces the amount fine fuels during the summer fire season. Repeated mowing over several years should reduce the density of the annual grass as long as mowing occurs before seed set.
Basal Area:: The area of the cross section of a tree at a height of 4.5 feet above the ground. The basal area of all trees in a given land area describes the degree to which an area is occupied by trees and is generally expressed in square feet per acre (ft2/acre)
Biomass Utilization and Disposal:: Biomass utilization is an alternative to open pile burning or landfill disposal. It would result in the use of the natural resource for beneficial purposes such as firewood, wood chips, compost, and other products. If residents cannot find an alternative to burning, then proper burning procedures should be followed.
Classic Interface:: Structures abut native vegetation with a clear line of separation between structures and the wildland vegetation along roads and fences. The fuels do not extend into the developed areas.
Defensible space:: Defensible space is defined as a minimum 30-foot area around houses and other structures where vegetation has been significantly modified or removed. The purpose of creating defensible space is to reduce the risk of losing homes and other property improvements to a wildfire (Smith and Adams, 1991). Defensible space is especially important in communities with structures directly adjacent to wildland vegetation, as in the intermix or rural interface conditions, where wildfires can spread quickly through the wildland fuels, threatening homes and lives.
Fire hazard:: As used in this report, vegetative factors that affect the intensity and rate of spread of a fire as well as urban factors that can facilitate or inhibit public safety and the containment of a fire in an interface area.
Fire regime:: A term used by fire ecologists to describe the periodicity and intensity of fire as specific to a plant community.
Fire risk:: As used in this report, potential ignition sources and factors that facilitate ignition of wildfires in or near interface areas.
Firebreaks:: A firebreak is a strip of land cleared of brush and trees down to the mineral soil.
Fuelbreaks:: A fuelbreak is a strip of land, strategically placed, on which a cover of dense, heavy, or flammable vegetation has been permanently changed to one of lower fuel volume or reduced flammability. Primary fuelbreaks flank ridge tops and valley bottoms and are used to control large fires. The recommended minimum width is 300 feet. Secondary fuelbreaks are used to break down large forested areas along roads, drainage ridges, communities and other valuable resources to support fires suppression into areas of less than 1,000 acres. Fuelbreak construction may include removing, controlling and possible replacing highly flammable vegetation with more fire resistant species. Ridge top fuelbreaks should have continuous length and width, which requires long-range planning. Fuels are reduced, ladder fuel is removed, and the canopy closure is reduced in fuelbreak treatments.
Fuel Reduction Treatment:: This treatment involves strategically locating blocks of land near communities where flammable vegetation has been permanently changed to one of lower fuel volume or reduced flammability. Fuel reduction treatments may also involve replacement of highly flammable vegetation with less flammable or more fire resistant species.
Fuel Loading:: An ocular estimate of the tons per acre (t/ac) of combustible fuels present on a site. Parameters for this assessment are less than 1 t/ac for “light fuels,” 1-4 t/ac for “medium fuels,” and >4 t/ac for “heavy fuels.”
Greenstrips:: Greenstrips are irrigated or usually non-irrigated bands of open space on private or public land (at least a minimum of 300 feet wide) that serve as a buffer zone between wildlands and adjacent urban development to promote safer environments. These areas are usually seeded to establish vegetation that is relatively fire resistant or burns slowly and with shortened flame lengths. Seedings also decrease soil erosion and prevent invasion of noxious weeds and other aggressive plants such as cheatgrass and Russian knapweed.
High Hazard Day:: Also known as a “red flag day”, a combination of conditions such as low humidity (less than 15%), high winds (>25 mph), and low fuel moisture create a high probability of ignition and subsequent increased fire intensity. Various agencies have different trigger points to establish a “high hazard day”.
Interface Condition:: Describes the density and distribution of structures with respect to the surrounding wildland environment. The four Interface Conditions are Rural, Intermixed, Occluded, and Classic.
Intermix Interface:: Structures are scattered throughout the wildland, with no clear boundary between the wildland vegetation and the community.
Occluded Interface:: This condition is usually within towns and cities where there are small islands of wildland fuels such as parks or open space. There is a clear boundary between the community and the wildland vegetation.
Red Card Certification:: A fire qualifications management system used by many state and all federal wildland fire management agencies to ensure that individuals are qualified to fight wildland fires.
Rural Interface:: Clusters of structures such as ranches or summer homes are widely spaced, sometimes more than a mile apart. The rural homes are surrounded by the wildland vegetation, with no clear line of separation between the fuels and homes.
Shaded fuelbreaks:: A shaded fuelbreak is created by altering surface fuels and increasing the height of the base of the live crown and opening the canopy by removing trees. This type of fuelbreak spans a wide range of understory and overstory prescriptions and methods of creation through manual, mechanical and the use of prescribed fires. A fuelbreak network system could be used to protect critical watersheds while more remote areas might have narrower fuelbreaks that might serve as anchor points for prescribed fires. A fuelbreak strategy can be effective even if fuelbreaks are not connected.
Thermal belt:: Heat absorbed by the soil during the day radiates from the soil surface of the mountain at night and rises into the free air. The radiation of heat makes the air closest to the soil surface colder than the free air. The cold air near the ground then moves downward into the valley. This movement of cold air to the valley forces the warm air in the valley upward. During the night there is a continuous interchange of cold air from the mountain surface and warmer free air from the valley. This condition creates a ‘belt’ of warm air, low humidity, and higher wind speed, leading to a higher risk of ignition in the belt area than elsewhere on the mountain.