Factors associated with crown damage following recurring mixed-severity wildfires and post-fire management in southwestern Oregon

摘要

Wildfires and post-fire logging and planting have a lasting influence on the quantity and arrangement of live and dead vegetation, which can, in turn, affect the behavior of future fires. In 2002, the Biscuit Fire re-burned 38,000 ha of mixed-conifer/evergreen hardwood forest in southwestern Oregon that had burned heterogeneously during the 1987 Silver Fire and then was subject, in part, to post-fire logging and planting. We measured vegetation cover and crown damage from at temporal sequence (1987, 2000, and 2002) of digital aerial photo-plots (plot size = 6.25 ha) within managed and unmanaged portions of the twice-burned landscape. We estimated the strength and nature of relationships between crown damage in the two fires while also accounting for the influence of several vegetation, topographic, weather, and management variables. On average, unmanaged plots within the reburn area had 58% of their live crown cover scorched or consumed by the Biscuit Fire (median = 64%). The level of re-burn crown damage was strongly related to the level of crown damage during the Silver Fire. Typically, the areas that burned severely in the Silver Fire succeeded to a mix of shrubs and tree regeneration (i.e. shrub-stratum vegetation), which then experienced high levels of Biscuit Fire damage. In contrast, the level of tree-stratum damage in the Biscuit Fire was largely independent of Silver Fire damage. Within plots that were salvage-logged then planted after the Silver Fire, on average 98% of the vegetation cover was damaged by the Biscuit Fire (median = 100%). Within the plots that experienced complete crown damage in the Silver Fire but were left unmanaged, on average 91% of the vegetation cover was damaged by the Biscuit Fire (median = 95%). Our findings suggest that in productive fire-prone landscapes, a post-fire mosaic of young regenerating vegetation can influence the pattern of crown damage in future wildfires.