An individual fire event (indeed, any disturbance event) can be characterized by its (a) magnitude, (b) patchiness, (c) extent, and (d) timing. Across many years, fires also occur at an average (e) frequency, which varies from one vegetation type and location to another. Taken together, the combination of those five characteristics can be used to define a fire regime, or the longer-term, historical pattern of fire events across time in any given place. In general, there are three broad categories of fire regimes based on frequency and severity—understory (frequent, low-severity), stand-replacement (infrequent, high-severity), and mixed-severity (mixed frequency and severity). Most western conifer forests support a mixed-severity fire regime.