Patterns of conifer tree regeneration following an autumn wildfire event in the western Oregon Cascade Range, USA

We investigated the effect of fire severity and environmental conditions on conifer tree regeneration 11 years after an autumn wildfire in the western Oregon Cascade Range. Conifer tree seedlings, including those of Pseudotsuga menziesii, established promptly and at high densities following fire, in contrast to long establishment periods documented for many other sites. P. menziesii, Tsuga heterophylla and Thuja plicata comprised 99.0% of the seedlings measured in the study. Pseudotsuga seedling density was greater on sites that had burned with moderate and high severity compared to low fire severity. Tsuga seedling density was greater on north aspects than on south aspects. Tsuga and Thuja seedling densities were correlated with pre-fire conspecific basal area. Coexistence of the three principal conifer species was more likely on sites that burned with moderate severity. We attribute the rapid initial establishment of Pseudotsuga observed in this study to the persistence of a canopy seed bank-a biological legacy not normally associated with Pseudotsuga forests. Environmental factors, fire severity and disturbance timing influence seedling establishment patterns, shaping future stand composition and development.