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Wildfire Risk

What is a Fire Regime?

A ‘fire regime‘ is the term given to the general pattern in which fires naturally occur in a particular ecosystem over an extended period of time. Scientists classify fire regimes using a combination of factors including frequency, intensity, size, pattern, season, and severity. Individual fires can vary greatly in severity, and the specific effects and risks caused by a fire will depend on the specifics of its fire regime. A classification system has been developed to describe the characteristics of a particular fire, determine which type of fire regime is common in a given ecosystem, and compare present fires with historical norms.

Wildfire - Trees Torching

Wildfire: Trees Torching (US Fish and Wildlife Service)

Four broadly accepted fire regime classifications are:

  • Understory fire regime: Little change to the structure of the ecosystem -- 80% or more of the dominant vegetation is able to survive the fire.
  • Stand-replacement regime: The most dramatic habitat modification - 80% or more of the dominant vegetation is killed as a result of fire. The structure of the above-ground vegetation is changed substantially.
  • Mixed-severity regime: Habitat modification varies depending on the severity of the fire and the susceptibility of the dominant vegetation to fire. Variation can also occur within a single fire.
  • Non-fire regime: Ecosystems where fire is not likely to occur.

Authored by Dan Weston, Intern, Institute for Natural Resources (2010)