Conifer regeneration in stand-replacement portions of a large mixed-severity wildfire in the Klamath-Siskiyou Mountains

Large-scale wildfires (similar to 10(4)-10(6) ha) have the potential to eliminate seed sources over broad areas and thus may lead to qualitatively different regeneration dynamics than in small burns; however, regeneration after such events has received little study in temperate forests. Following a 200 000 ha mixed-severity wildfire in Oregon, USA, we quantified (1) conifer and broadleaf regeneration in stand-replacement patches 2 and 4 years postfire; and (2) the relative importance of isolation from seed sources (live trees) versus local site conditions in controlling regeneration. Patch-scale conifer regeneration density (72%-80% Douglas-fir (Pseudotsuga menziesii (Mirb). Franco)) varied widely, from 127 to 6494 stems.ha(-1). Median densities were 1721 and 1603 stems.ha(-1) 2 and 4 years postfire, respectively, i.e., similar to 12 times prefire overstory densities (134 stems.ha(-1)). Because of the complex burn mosaic, similar to 58% of stand-replacement area was <= 200 m from a live-tree edge (seed source), and similar to 81% was <= 400 m. Median conifer density exceeded 1000 stems.ha(-1) out to a distance of 400 m from an edge before declining farther away. The strongest controls on regeneration were distance to live trees and soil parent material, with skeletal coarse-grained soils supporting lower densities (133 stems.ha(-1)) than fine-grained soils (729-1492 stems.ha(-1)). Other site factors (e. g., topography, broadleaf cover) had little association with conifer regeneration. The mixed-severity fire pattern strongly influenced the regeneration process by providing seed sources throughout much of the burned landscape.