Quantifying impacts of forest fire on soil carbon in a young, intensively managed tree farm in the western Oregon Cascades

Abstract

AbstractForest soils of the Pacific Northwest contain immense amounts of carbon (C). Increasing acreage burned by severe wildfire in the western Oregon Cascades threatens belowground C stocks. The objective of this research was to quantify the changes in soil C stocks, nitrogen (N) stocks, and relevant chemical and physical parameters after a severe wildfire in a young, intensively managed Pseudotsuga menziesii (Douglas‐fir) tree farm in the western Oregon Cascades. This longitudinal study was originally established to detect soil C changes after a harvest; therefore, it offers insight into long‐term soil C dynamics after compounding disturbances. Forest floor and 0–30 cm depth soil samples were collected for comparison before and after the fire and were then split into size fractions to assess the fire's effect on different grain sizes and forest floor compositions. Overall, soil C was approximately 40 Mg C ha−1 lower after the fire, equivalent to approximately 30% of soil C stocks. Of these decreases, two‐thirds were in the forest floor and one‐third were in the mineral soil. C stock losses were driven by changes in mass in every composite level. C concentration was unchanged in most levels while N concentration increased in certain levels. Losses extended further belowground than most previously studied soil C decreases from severe wildfire. The effects of wildfire on soil C stocks in industrial tree farms should be further explored to determine long‐term trajectories of soil C and N.