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Increasing fire severity and warmer, drier postfire conditions are making forests in the western United States (West) vulnerable to ecological transformation. Yet, the relative importance of and interactions between these drivers of forest change remain unresolved, particularly over upcoming decades. Here, we assess how the interactive impacts of changing climate and wildfire activity influenced conifer regeneration after 334 wildfires, using a dataset of postfire conifer regeneration from 10,230 field plots. Our findings highlight declining regeneration capacity across the West over the past four decades for the eight dominant conifer species studied. Postfire regeneration is sensitive to high-severity fire, which limits seed availability, and postfire climate, which influences seedling establishment. In the near-term, projected differences in recruitment probability between low- and high-severity fire scenarios were larger than projected climate change impacts for most species, suggesting that reductions in fire severity, and resultant impacts on seed availability, could partially offset expected climate-driven declines in postfire regeneration. Across 40 to 42% of the study area, we project postfire conifer regeneration to be likely following low-severity but not high-severity fire under future climate scenarios (2031 to 2050). However, increasingly warm, dry climate conditions are projected to eventually outweigh the influence of fire severity and seed availability. The percent of the study area considered unlikely to experience conifer regeneration, regardless of fire severity, increased from 5% in 1981 to 2000 to 26 to 31% by mid-century, highlighting a limited time window over which management actions that reduce fire severity may effectively support postfire conifer regeneration. [ABSTRACT FROM AUTHOR]

Context: Landscape and local factors govern tree regeneration across heterogeneous post-fire forest environments. But their relative influence is unclear—limiting the degree that managers can consider landscape context when delegating resources to help stand-replacing patches restock successfully. Objectives: We investigated how landscape and local factors shape tree regeneration across heterogeneous post-fire forest environments. Our research questions were: What is the relative influence of landscape and local factors on tree species presence (RQ1) and stocking density (RQ2) at stand-replacing patches? Do thresholds occur when landscape factors are influential (RQ3)? Methods: We sampled landscape and local variables at 71 plots near Jackson, Wyoming, United States. We used Random Forests to investigate how local and landscape variables affect post-fire tree recovery. Relative influence was determined using mean decrease in accuracy. Partial dependence plots were used to visualize whether thresholds occurred for variables with mean decrease in accuracy > 15%. Results: Landscape factors like seed source area were associated with subalpine fir presence and stocking density. But different thresholds occurred. Specifically, subalpine fir presence required 10% seed source area, while stocking density required 40%. Northeast aspects surrounded by > 10% seed source area were most likely to support subalpine fir presence. Conversely, local factors like soil nutrients were associated with lodgepole pine presence, highlighting effects of different regeneration strategies. Conclusions: Landscape factors bolster spatial resilience and help stand-replacing patches restock naturally. But landscape factors do not support tree regeneration equally across heterogeneous post-fire forest environments. Consequently, considering stand-replacing patches in their landscape context will be critical for future spatial action planning. [ABSTRACT FROM AUTHOR]