Evaluating a century of fire patterns in two Rocky Mountain wilderness areas using digital fire atlases

Changes in fire size, shape, and frequency under different fire-management strategies were evaluated using time series of fire perimeter data (fire atlases) and mapped potential vegetation types (PVTs) in the Gila – Aldo Leopold Wilderness Complex (GALWC) in New Mexico and the Selway–Bitterroot Wilderness Complex (SBWC) in Idaho and Montana. Relative to pre-Euro-American estimates, fire rotations in the GALWC were short during the recent wildfire-use period (1975–1993) and long during the pre-modern suppression period (1909–1946). In contrast, fire rotations in the SBWC were short during the pre-modern suppression period (1880–1934) and long during the modern suppression period (1935–1975). In general, fire-rotation periods were shorter in mid-elevation, shade-intolerant PVTs. Fire intervals in the GALWC and SBWC are currently longer than fire intervals prior to Euro-American settlement. Proactive fire and fuels management are needed to restore fire regimes in each wilderness complex to within natural ranges of variability and to reduce the risk of catastrophic wildfire in upper elevations of the GALWC and nearly the entire SBWC. Analyses of fire atlases provide baseline information for evaluating landscape patterns across broad landscapes.