Determining whether forest landscapes can maintain their resilience to fire–that is, their ability to rebound and sustain their current composition and structure–in the face of rapid climate change and increasing fire activity is a pressing challenge throughout the American West. Many western forests are well adapted to fire, and even subalpine forests that experience infrequent, high- severity fires historically recovered long before they burned again. However, current rates of warming portend a mismatch between historical and future fire regimes. Our project quantified multiple dimensions of resilience for Northern Rocky Mountain forests and developed innovative, widely applicable scientific methods for operationalizing resilience concepts. We engaged fire, fuels and resource managers at the outset through “Dimensions of Resilience” workshops in February 2017. We jointly identified multiple desired characteristics to sustain throughout the 21st century and potential simulation landscapes. Informed by this input, we combined state-of-the-art projections of future climate and fire with extensive data on post-fire forest dynamics to model alternative future scenarios and evaluate forest resilience. We asked: (1) How and why might warming climate and changing fire regimes push forest stands over a tipping point? (2) Where and when might projected changes in climate and fire activity interact with management to enhance or erode landscape resilience? (3) How do stand and landscape indicators of resilience scale to the Northern Rockies ecoregion, and what geographical areas are most likely to be vulnerable or resilient to changing climate and fire regimes? We re-convened with stakeholders through “Learning about Resilient Futures” workshops in February 2020 to jointly interpret effects of changing climate, fire and management on forest landscape resilience. Objectives were achieved (15 papers published, 5 in progress; 3 MS theses; 3 PhD dissertations), and the in-person workshops fostered excellent communication between scientists and managers.
Under a hotter-drier climate, forest extent is projected to shrink substantially during the 21st century, and remaining forests will be younger and sparser than current forests. Postfire tree regeneration, which is critical for sustaining forest resilience, will decline if more frequent fires reduce local seed availability, larger burn patches exceed effective dispersal distances, and postfire climate conditions are not conducive to seedling establishment. Forests dominated by fire-sensitive tree species (e.g., Picea engelmannii, Abies lasiocarpa, Pinus contorta var. latifolia) are likely to show the greatest declines, whereas forests dominated by fire resisters (e.g., Pseudotsuga menziesii, Larix occidentalis) and reprouters (e.g., Populus tremuloides) will be more resilient. Declining fire rotations may pass a tipping point after which forest extent sharply declines. Climatically suitable areas for three forest-dependent vertebrates often did not intersect locations where simulated vegetation structure was also suitable; projections based on climate or vegetation alone are likely to misrepresent future habitat availability. Our results also suggested a peak in both high-severity fire and fire risk in the wildland-urban interface (WUI) during the mid-21st century, although annual area burned continued to increase. In the WUI, clustering developments and applying fuels treatments on 10 to 30% of the landscape every 10 years can reduce fire risk across multiple scales. In subalpine landscapes managed for wilderness values, fire suppression is unlikely to alter the trajectory of forest change because forest dynamics will be driven primarily by large fire years and increasingly arid conditions. "Bending the curve" of greenhouse gas emissions to stabilize atmospheric concentrations by mid-21st century will dampen the consequences of climate warming for forest landscapes.