Limited conifer regeneration, but widespread regeneration of aspen seedlings following the Cameron Peak Fire, northwestern Colorado

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 surveyed tree regeneration at 34 sites across upper montane and subalpine forests that burned in the Cameron Peak Fire located in northern central Colorado. All sites were located in areas that: (a) burned at high or moderate severity and (b) were located >50 m and <1000 m away from a pre-fire patch of aspen. At each site, we recorded the coordinates, elevation, slope, aspect, and pre-fire tree-species composition. Tree regeneration was then surveyed in two perpendicular 2 x 50 m transects that intersected at the midpoint. 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 coarse woody debris. Further we found aspen seedlings often outnumbered conifer seedlings and occurred within the same local neighborhood as conifer seedlings.