Three decade record of contiguous-US national forest wildfires indicates increased density of ignitions near roads

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From 1992 to 2024, in all 8 contiguous-US Forest Service regions combined, wildfire-ignition density was lowest in designated wilderness areas (1.75 fires/1000 hectares), followed closely by Inventoried Roadless Areas (1.97 fires/1000 ha). The highest wildfire-ignition density was in lands within 50 m of roads (7.99 fires/1000 ha), and the second highest wildfire-ignition density was in other national forest lands outside of the 50-m road buffers but not in wilderness or roadless areas (3.50 fires/1000 ha). For human-caused, natural, and undetermined fires, wildfire-ignition density decreased as distance to road increased, irrespective of designation categories such as “wilderness” or “roadless.” In lands between 0 and 250 m from roads, 6 fires ignited per 1000 ha, whereas fewer than 2 fires ignited per 1000 ha at a distance class of over 2000 m from roads. Mean fire size varied by where the fire started: it was greatest in wilderness areas (239 ha), followed by Inventoried Roadless Areas (135 ha), roaded national forest lands outside of Inventoried Roadless Areas, wilderness, and the 50-m buffer (62 ha), and lands within the 50-m road buffer (49 ha). We found, however, that the largest 2% of fires had similar mean sizes and ignition densities regardless of where they started.