OOS 23-6 - Nature of the beast: What climate change means for the ecology and management in low-frequency, high-severity fire regimes

Warming climate is a dominant driver behind changes to forest fire regimes and associated management challenges in an era of rapid change. To date, most climate adaptation literature has focused on frequent-fire forests, where challenges are often associated with reckoning with the effects of past fire suppression/exclusion interacting with increased fire potential under warming temperatures. However, infrequent (fire rotations spanning centuries) and stand-replacing fire regimes (large patches of high-severity fire with >90% basal area mortality) comprise a significant amount of global forest area, yet have received relatively little attention in the climate adaptation arena. In this talk we first review why adaptation options differ between frequent- and infrequent-fire systems. We then explore commonalities and uncertainties in climate adaptation options within the infrequent and stand-replacing fire regimes of the Pacific Northwest and Northern Rocky Mountains. Within both regions, we observed two types of fires with distinct adaptation implications: large-footprint fires driven by top-down factors (e.g. wind) that result in a narrower range of proportion burned as stand-replacing, and generally smaller-footprint fires driven more by bottom-up influences (e.g., fuel and topography) with a broader range of proportion of stand-replacing area. These differences in fire event type and effects can inform both pre- and post-fire adaptation strategies, with specific management options and risks differing by anticipated fire size and drivers. For example, fuel treatments appear largely ineffective during wind-driven events but may be beneficial prior to smaller fires, depending on management objectives. But given fuel treatments fundamentally alter the character of these forests (unlike frequent-fire systems), and the impossibility of knowing where a fuel treatment will interact with a smaller future fire, when does fuel treatment implementation make sense? We end by considering this and other questions as we examine implications for adaptation given uncertainties in future fire event size with climate change. This framework can be useful for pre- and post-fire management and policy in infrequent-fire forests broadly.