Influence of Increasing Fires on Mixed Conifer Stand Dynamics in the U.S. Southwest

(1) Stand-replacing fires may threaten the continued stability of mixed conifer forests in the U.S. Southwest. Increasing fire frequency and severity have made post-fire forest recovery trajectories uncertain for many coniferous species, potentially leading to long-term shifts in forest structure and composition. (2) The purpose of this study was to examine post-fire stand dynamics over a 10-year period, using a network of permanent plots established prior to wildfire events across Arizona and New Mexico. We assessed changes in overstory composition, regeneration, and fuel loading across different fire severities. (3) High severity fire caused near-total overstory mortality, with little to no conifer regeneration and abundant sprouting hardwood regeneration. Lower severity fire was more favorable to fire-tolerant conifer species; however, mortality among mature trees was high, and fire-intolerant conifers were either diminished or extirpated completely. (4) In high severity fires, changes in overstory and understory structure and composition may be long-lasting. Additionally, increased fuel loads following high severity fire suggests a heightened risk of reburns, potentially perpetuating ecotype conversion. Our findings highlight the need for active management strategies, including reforestation and fuel reduction treatments, to support forest resilience for mixed conifer ecosystems in the US Southwest and similar forest types in other regions in the face of ongoing climate and fire regime changes.