Glossary
Bud kill (or crown kill, %) is the portion of the tree’s buds killed during the fire.
Bulk density (ρb, kg m-3) of a fuel component is the mass of the fuel divided by the volume of space within it resides (Keane 2015).
Canopy base height (CBH, m) is defined as the vertical distance between the ground surface and the base of the canopy where there is sufficient canopy fuel to propagate fire vertically (Scott & Reinhardt, 2001).
Canopy bulk density (CBD, kg m-3) is the mass of available canopy fuel per unit canopy volume (Scott & Reinhardt, 2001). CBD is a stand property that can be calculated using the canopy fuel load and the canopy depth (Scott 2012).
Canopy closure (%) is a point measure of site occupancy by vegetation.
Canopy cover (CC, %) is the vertically projected cover of tree crown perimeters onto the ground (Scott, 2012). CC did not equal canopy closure
Canopy depth (CD, m) is the vertical distance between stand height and the crown base height.
Canopy fuel load (t ha-1) is the oven-dry mass of available canopy fuel per unit ground area (Scott, 2012). It is usually assumed that only the foliage and a small branchwood (0-3 mm live and 0-6mm dead) are available for combustion (Scott & Reinhardt, 2001).
Canopy fuels are composed by large trees and shrubs with most of the fine biomass growing above the upper surface fuel limit (Pyne 1996). are referred to as
Charred twig diameter of shrubs (mm) refers to the diameter of the smallest twig remaining on the shrub-like woody skeleton.
Coarse fuels are composed of wood material higher than 25 mm of diamter (branches, stems and logs)
Combustibility refers to the ease with which the fuel burns, releasing enough energy to consume itself and ignite surrounding fuel.
Combustion rate (g s-1) can be quantified as the mass weight loss during combustion.
Crown scorch (%) is the portion of the tree’s foliage killed during a fire
Dead fuel moisture (DFMC, %) refers to the ratio of water mass over the dry mass of dead plant material. Moisture exchanges in dead fuels are mainly controlled by physical processes and clearly depend on atmospheric conditions.
Downed dead woody debris of fallen stems, branches and logs on the forest floor. They are often separated into fine woody debris (FWD) and coarse woody debris (CWD) depending if the diameter of the woody fuel particle is less or equal and higher than 8 cm, respectively (Keane, 2015).
Duff refers to to the F and H decomposed material below the litter and above the mineral soil. Due to differences in fuel properties (moisture, mineral content,…) duff can be separated in the upper and lower duff corresponding to the F and H layers respectively.
Ecosystem carbon losses (kgC ha-1), in fire science, refers to the amount of organic carbon that is release into the atmosphere or mobilized into the aquatic systems
Fine fuels are composed of leaves and branches with a diameter lower than 25 mm (1 and 10 h fuel)
Fire intensity is the energy released during various phases of combustion (flaming, glowing, smoldering) and it is useful to describe the propagation of a fire and predict fire effects. However, sometimes fire intensity is used incorrectly to describe fire effects (Keeley, 2009): The same fire intensity can produce different fire severity, depending on the residence time and the ecosystem type.
Fire severity relates to the amount of organic matter consumed by fire, and it is often misused to describe a broad range of impacts caused by fire (Keeley 2009).
Fireline intensity (kW m-1) describes the energy flux from the fire per unit of front length, regardless of its depth (Scott 2012).
Flame height (FH, m) is measured vertically at a single point.
Flame length (FL, m) is the distance from the base of the flame zone to the tip of continuous flaming (Scott, 2012). FL is a better descriptor of fire intensity under windy conditions or on slopes than flame height
Flame zone depth (FD, m) is measured as the flame width parallel to the fire spread direction
Flaming front rate of spread (ROS, m s-1) is the linear rate of advance of a fire front into unburned fuel in the direction perpendicular to the fire front (Scott, 2012). It is one of the variables used to describe fire behavior, and of great interest for anticipating impacts and managing potential interventions.
Flammability refers to the ability of a fuel to burn and encompasses three variables: ignitability, combustibility and sustainability (Trabaud 1976).
Forest floor consumption estimates the changes in forest floor layers caused by fire.
Fuel bed is a general term referring to the complex arrangement of fuel types in a given area. Although it can include the different layers of a fuel complex, it is frequently used to describe the surface fuel.
Fuel complex refers to thequantity, and arrangement of the fuels
Fuel load (W, Kg m-2) is the amount of living and dead mass expressed as the dry weight of fuel per surface area.
Fuel Loading Models is a set of fuelbed inputs needed by a particular fire behavior or fire effects model (Scott & Burgan 2005).
Fuel structure refers to the spatial configuration of the fuel complex, and includes an array of different variables that are mostly used in fire behavior modeling.
Grass curing is a measure of “greenness” and the degree of curing is defined as the percentage of the aboveground herbaceous material that is dead (Flavelle 2008).
Grass ignitability or the angle at which a fine fuel particle breaks that estimate the DFMC of fine fuel particles.
Ground fuels are organic material beneath the soil surface, such as peat, duff (i.e., decomposed soil organic layers), roots or decomposing wood
Heat capacity (kJ g-1 ºC-1) is a specific property of each substance related to the amount of heat that is needed to change one degree of temperature per mass unit.
Heat per unit of area (HPA, MJ m-2) is the amount of heat released per unit ground area during the relatively short duration of continuous flaming as the flaming front passes, without including post-frontal flaming and smoldering combustion (Scott, 2012).
Heat release (kJ g-1) is the energy release during a fire per unit of mass.
Heat transfer is the energy that moves from one to another point, heating it.
Herbaceous fuel load (kg m-2) refers to the mass of non-woody vascular plants, including ferns, grasses, and forbs. Small woody hemicryptophytes can also be included due to the small branches’ diameter. Herbaceous fuel complexes are characteristic of grasslands, steppes, savanna, open woodlands and rain-fed cereal crops. The availability of herbaceous fuel varies drastically throughout the annual life cycle—changing from living to dead fuel within a matter of a few weeks due to the high surface-to-volume (SAV) ratio of herbaceous particles and the phenology of most herbaceous species.
Ignitability indicates how easily a fuel burns when exposed to a heat source.
Ladder fuels Small trees or shrubs that constitute surface fuels but whose foliage extends between the upper limit of the surface fuel and canopy fuels (Menning & Stephens, 2007).
Litter, in fire science, corresponds to the recently fallen leaves and branches accumulated in the L or Oi horizon. Litter is usually considered a surface fuel due to the moisture dynamics and effect on fire behavior.
Live fuel moisture content (LFMC) refers to the ratio of water mass over the dry mass of living plants. Variations in moisture of fine living fuels are related not only to meteorological factors and soil water availability, but also to ecophysiological characteristics of plant species (Gabriel et al. 2021).
Organic forest floor can be separated into different layers according to its decomposition status. Three organic layers are usually considered (e.g. Klinka et al. 1981): The litter (L or Oi) layer, corresponding to recently fallen leaves and twigs (<1 year old); the fermentation (F or Oe) layer corresponding to fragmented and moderately decomposed leaves and fine branches; and the humus (H or Oa) layer, corresponding to highly decomposed organic material, in which it is difficult to recognize the original tissues and structures.
Packing ratio (cm3 cm-3) is the proportion of the total space occupied by the mass, and it is opposite to porosity.
Porosity, see packing ratio
Residence time (min) refers to the time the heating is above a temperature threshold at a given point
Resprouting ability refers to the capacity of plants to regenerate from protected meristems following substantial loss of aboveground biomass.
Shrub mortality (nº ha-1) refers to the number of shrub killed by fire per unit area. As with trees, a total absence of leaves indicates death in species that do not resprout, whereas the lack of resprouts must be assessed for at least three years following the fire to confirm mortality in resprouting species.
Shrub-like fuel load refers to the biomass of woody plants (i.e., chamaephyte, nano- and macrophanerohyte) that grow in shrublands or in the understory of the forest. It is composed of mostly fine fuels, with branches thinner than 75 cm in diameter, and can retain a substantial amount of standing dead fuel (leaves and branches). Some authors classify shrub fuel into leaves and woody components with a diameter of less than 6 mm, and into stems and branches of larger diameter (e.g., Brown et al. 1982; De Cáceres et al. 2019), due to their differing dynamics throughout the year or during prolonged droughts (Gabriel et al. 2023).
Soil fire severity is generally defined as the degree to which soil organic matter is consumed or mineralized as a consequence of fire, particularly within the forest floor and upper mineral soil horizons.
Soil hydrophobicity describes a condition where soil repels, rather than absorbs water, resulting in increased surface runoff.
Soil surface impact is defined as the degree of change caused by fire
Stand height (SH, m) is the average height of the largest or dominant trees in the stand.
Stem char height (m), defined as the maximum vertical height of blackened bark on a tree bole above ground level
Surface fuel bed depth (δ, m) refers to the average height of surface fuel in the combustion zone of a spreading fire front. It is a key descriptor of surface fuel models used to characterize straightforwardly the combined depth of the surface fuel layers, including dead and live woody fuel, herbaceous fuel and litter.
Surface fuels are the combustible material on the surface of the soil, such as recently fallen leaves, branches and logs, and the standing living or dead mass of herbs and woody plants between the ground and an arbitrary limit of 1.3 m or 3.0 m above
Suspended dead tree leaves in the branches of shrubs can significantly increase the dry fuel load in surface and ladder layers. However, its fuel load is difficult to estimate.
Sustainability (seg.) describes the stability of burning rate, that is, the extent to which a fuel continues to burnover time. It can be restricted to the flame duration or can also include the smoldering phase.
Temperature (ºC) is a physical quantity which describes the energy of a particle,
Time-lags. Dead fuel has traditionally been grouped in four diameter classes according to the amount of time necessary for a fuel particle to equilibrate its moisture to the 2/3 of the moisture content of the environment Fosberg et al., 1970): 1-h time-lag fuel with a diameter lower than 6 mm; 10-h time-lag fuel with a diameter between 6 m and 25 mm; and 100-h time-lag fuel with a diameter between 25 mm and 76 mm, and 1000-h time-lag with a diameter thicker than 76 mm.
Time-temperature integral (ºC min) refers to the time accumulated temperature above a temperature threshold, and can be a proxy of the heat accumulated energy in a given point.
Tree mortality (nº ha-1) refers to the number of trees killed by fire per unit area.