Exposure and carbon risk for mature and old-growth forests from severe wildfire in the Pacific Northwest, U.S.A.

Mature and old-growth forests (MOG) provide essential ecosystem services, yet they face increasing threats. Currently, high-intensity, high-severity wildfires are the main driver for loss of MOG on federally managed forests across the United States. Quantifying MOG forests with greatest exposure to stand-replacing wildfires provides essential information for land managers. We integrated geospatial data from fire behavior simulations (fire intensity), fire refugia prediction (fire severity), forest type mapping, and carbon estimates to assess exposure of MOG forests to stand-replacing wildfires in national forests within the Northwest Forest Plan region of the Pacific Northwest. We show that ca. 75% of MOG exposure is in areas with historically frequent, low-severity fire, that fire refugia capacity may help mitigate exposure between 6 to 21% across forest types, and expected carbon emissions are greatest in the Klamath Mountains ecoregion. Our findings demonstrate the geography of exposure for MOG and aim to inform regional priorities for MOG stewardship.