Long-Term Legacies of Wildfire
Collaborators:	Tom Giesen, Kermit Cromack (OSU)
Funding:	OSU Richardson Fellowship, USGS

Episodic stand-replacing wildfire is a significant disturbance in mesic and moist Douglas-fir forests of the Pacific Northwest, yet few studies report landscape-level effects of wildfire disturbance on soil carbon (C) and nitrogen (N) pools. This work examines 24 western Oregon Cascades forest stands with known fire histories to examine long-term impacts of stand replacing wildfire on forest floor Oe and Oa, and surface mineral soil (0-10 cm) C and N. Stands are divided into twelve burned ~ 150 years ago ("young") and 12 burned ~ 550 years ago ("old”).

Results from the first phase of this work indicate that forest floor pools of C and N are significantly greater in old than young stands, primarily due to differences in forest floor mass. Forest floor C and N concentrations and C:N ratios did not differ by time since fire, yet potential N mineralization rates are significantly higher in old sites, and nitrification (while negligibly small) is greater in young sites. Mineral soils did not exhibit any significant between young vs. old forests. These results suggest that long-return intervals between wildfires can have multi-century impacts on forest floor dynamics and N biogeochemistry in Pacific Northwest Douglas-fir forests, contributing to N limitation and low nitrification in the region.

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