Fire severity and tree seedling establishment in Abies magnifica forests, southern Cascades, Oregon

To determine the relationship between fire severity and tree seedling establishment, we investigated landscape pattern and composition, fire history, and tree seedling establishment on recent natural burns in Shasta red fir (Abies magnifica var. shastensis) forests of Crater Lake National Park in the southern Oregon Cascade Range. Fire severity classes, defined by basal area mortality, were mapped on three burned sites (29-197 ha). Variation in fire severity contributed to a landscape mosaic of patches with varying size, shape, forest stand structure, and tree species' composition. Post-fire tree regeneration was numerically dominated by red fir in all fire severity classes, but seedling establishment and growth varied among severity classes. Density of red fir seedlings was highest in low- and moderate-severity patches, and lower in high-severity patches and unburned areas. Height growth of red fir seedlings increases with fire severity. Variations in fire severity in red fir forests appear to be a major influence on post-fire stand structure and species composition, successional pathways, and resulting landscape patterns. Our results suggest that drought may be an important mortality agent controlling red fir regeneration on these burned sites. Red fir seedling establishment occurs in pulses, usually 3-4 yr after fire.