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

摘要

Large-scale wildfires (∼ 104-106 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 200000 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., ∼12 times prefire overstory densities (134 stems-ha-1). Because of the complex burn mosaic, ∼58% of stand-replacement area was ≤200 m from a live-tree edge (seed source), and ∼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.