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Table 2 Fire regime groups (FRG) used in characterizing unburned islands within fires in the Inland Pacific Northwest from 1984 to 2014. Adapted from Malesky et al. 2018

From: Characterizing persistent unburned islands within the Inland Northwest USA

Fire regime Frequency    Example cover type from
group (yr) Severity Severity description study area
I 0 to 35 Low or mixed Generally low-severity fires replacing less than 25% of the dominant overstory vegetation; can include mixed-severity fires that replace up to 75% of the overstory (typical of perennial grasslands) Ponderosa pine; dry mixed conifer forest
II 0 to 35 Replacement High-severity fires replacing greater than 5% of the dominant overstory vegetation (annual grasslands and some forests with frequent surface fires) Grassland
III 35 to 200 Mixed or low Generally mixed severity; can also include low-severity fires (many forests and shrublands) Big sagebrusha, lodgepole pineb
IV 35 to 200 Replacement High-severity fires (forests and shrublands) Big sagebrush, lodgepole pine
V ≥200 Replacement or any severity Generally, replacement severity; can include any severity type in this frequency range (some moist forests, tundra, and deserts) Very sparse big sagebrush steppe; spruce–fir forest
  1. a(Artemisia tridentata Nutt.)
  2. b(Pinus contorta Douglas ex Loudon)