Background <p>Changing fire regimes and climate conditions have decreased postfire conifer regeneration densities in many ecosystems across Western North America. In the Southern Rocky Mountains, sparse postfire regeneration of conifers has often been accompanied by abundant regeneration of quaking aspen, much of which is from vegetative resprouting. While aspen also produces abundant lightweight seed that can disperse great distances, we know considerably less about the patterns and drivers of postfire establishment of aspen from seed. To understand the potential for severe fire to catalyze shifts to aspen-dominated forests, we studied conifer-dominated forests that burned at high severity and asked: (1) how does postfire regeneration of conifers and aspen vary across sites? (2) how are aspen and conifer seedlings distributed within sites? and (3) how do site and microsite conditions influence aspen seedling establishment? To answer these questions, we conducted field surveys at 32 sites within the burn scar of the Cameron Peak fire, northwestern Colorado.</p> Results <p>Two years following fire, we found widespread but highly variable establishment of aspen seedlings, despite the absence of aspen in the pre-fire stand. Aspen seedlings were more likely to occur at higher elevations, where they were often clustered within concave microsites with bryophyte substrates and near large CWD. Further, we found aspen seedlings often outnumbered conifer seedlings and occurred within the same local neighborhood as conifer seedlings.</p> Conclusions <p>Increased fire frequency, severity, and extent in Western North America may exceed the capacity of some formerly conifer-dominant forests to maintain historical distributions, while conditions following high-severity burns may allow for aspen seedling establishment and the expansion of aspen populations.</p>