Fire intensity, fire severity and burn severity: a brief review and suggested usage

Abstract

Several recent papers have suggested replacing the terminology of fire intensity and fire severity. Part of the problem with fire intensity is that it is sometimes used incorrectly to describe fire effects, when in fact it is justifiably restricted to measures of energy output. Increasingly, the term has created confusion because some authors have restricted its usage to a single measure of energy output referred to as fireline intensity. This metric is most useful in understanding fire behavior in forests, but is too narrow to fully capture the multitude of ways fire energy affects ecosystems. Fire intensity represents the energy released during various phases of a fire, and different metrics such as reaction intensity, fireline intensity, temperature, heating duration and radiant energy are useful for different purposes. Fire severity, and the related term burn severity, have created considerable confusion because of recent changes in their usage. Some authors have justified this by contending that fire severity is defined broadly as ecosystem impacts from fire and thus is open to individual interpretation. However, empirical studies have defined fire severity operationally as the loss of or change in organic matter aboveground and belowground, although the precise metric varies with management needs. Confusion arises because fire or burn severity is sometimes defined so that it also includes ecosystem responses. Ecosystem responses include soil erosion, vegetation regeneration, restoration of community structure, faunal recolonization, and a plethora of related response variables. Although some ecosystem responses are correlated with measures of fire or burn severity, many important ecosystem processes have either not been demonstrated to be predicted by severity indices or have been shown in some vegetation types to be unrelated to severity. This is a critical issue because fire or burn severity are readily measurable parameters, both on the ground and with remote sensing, yet ecosystem responses are of most interest to resource managers.

Burn severity influence on post-fire vegetation cover resilience from Landsat MESMA fraction images time series in Mediterranean forest ecosystems

“…In high seeding tree communities of Mediterranean P. halepensis, different authors (Broncano et al, 2005;Kazanis and Arianoutsou, 2004;Trabaud, 2002) suggest recovery times starting from 15 years. Local attributes like climate, terrain characteristics, or vegetation type influence vegetation cover recovery time (Baeza et al, 2007;Keeley, 2009).…”

How Robust Are Burn Severity Indices When Applied in a New Region? Evaluation of Alternate Field-Based and Remote-Sensing Methods

“…Common measurements of fire severity quantify the consumption of organic materials, such as the loss of litter and duff, canopy fuel consumption (often measured by the height or percentage of scorch and char on trees), or twig diameter remaining on residual branches. Measurements may also include additional proxies for consumption, such as tree mortality and white ash deposition [17,18]. In forested ecosystems fire severity has often been classified solely by overstory tree mortality, while incorporating other variables secondarily.…”

Modelling natural disturbances in forest ecosystems: a review

“…In contrast, second order fire effects, such as post-fire vegetation response, may be independent of severity (e.g., Keeley, 2009). Many fire-adapted species have the ability to sprout from below-ground parts after a fire event.…”