Background <p>Giant sequoias are among the oldest and most massive trees in the world, and they are also among the most fire resilient. Historically, they experienced frequent, predominantly low- to moderate-severity fire that kept fuel loads low. However, over a century of fire exclusion has greatly increased fuel loads, which is interacting with the warming climate to increase wildfire activity and severity in the giant sequoia range. While the existing literature has documented mortality rates and explored the linkage between tree-level characteristics and delayed mortality, this study is the first to explore the role of forest structure in individual sequoia mortality. We sampled three giant sequoia groves that burned in the 2020 Castle Fire to explore the drivers of both individual large sequoia mortality and stand-level fire severity. For individual large sequoia mortality, we examined individual tree characteristics, topography, and the role of forest structure at two neighborhood sizes (7.5&#xa0;m and 15&#xa0;m surrounding the focal tree). We also explored how forest structure and topography influence stand-level basal area mortality.</p> Results <p>We surveyed 620 large sequoias (&gt; 1&#xa0;m diameter), 41% of which were dead. An additional 31 trees were likely to die or vulnerable to mortality as a result of elevated crown loss, mostly in high-severity areas. None of our forest structure variables were significant predictors of individual large sequoia mortality at either neighborhood scale. While no relationship was detected, we note that the majority of our individual large sequoias had surrounding tree densities that were well above target conditions for fire resilience. In terms of individual tree characteristics, we found that trees with smaller crown ratios were significantly more likely to die, likely because they had less photosynthetic tissue to lose, which could suggest that these trees are priorities for treatment. When considering stand-scale effects (plot data that was sampled on a grid across these groves), we found no significant predictors for the full model predicting 100% basal area loss (i.e., stand replacement). However, when focusing on the plots that did not experience stand replacement (e.g., 1–99% basal area mortality), increased tree density was associated with increased mortality. We were unable to test fire weather variables because all of our plots burned on the same 4 days which were characterized by fairly uniform and severe fire weather, which may have eclipsed the importance of some of the forest structure variables.</p> Conclusions <p>Even though severe fire weather conditions were dominant when our plots burned, and most had extremely high tree densities, our results still highlight the importance of tree density as a driver of severe fire effects at the stand-level. While we detected no relationship between individual large sequoia mortality and tree density immediately surrounding them, most of our study trees were surrounded by very high densities; it is possible that targeted treatments that reduce tree density closer to restoration goals still have the potential to help reduce large sequoia mortality. This is consistent with a continually growing body of research that suggests that reductions in tree density in post-settlement forests have the potential to reduce fire severity and preserve highly valued ecosystems like the giant sequoia.</p>