Soil Nitrogen Transformations and Surface Runoff Chemistry In Post-Wildfire Restoration Treatments.

The 2000 Storrie Fire (Lassen NF, northern Sierra Nevada) presented an opportunity to evaluate the effects of post-wildfire management treatments on ecosystem processes and properties.  Our objective was to compare changes in ecosystem processes between untreated burned stands and a range of management treatments within an area burned by a high severity wildfire. Eight post-fire treatments were selected:  high severity wildfire with no treatment, low severity wildfire with no treatment, salvage (seedlings planted), plantation (salvage followed by intensively managed plantation), brush mastication, grapple pile (disturbance area between piles), fall burn of grapple piles (dry fuels), spring burn of grapple piles (wet fuels). Field measurements included: soil total CO2 efflux, net N transformation rates, soil total C and N, forest floor biomass, C and N, soil temperature, soil water content, bulk density, and overland flow chemistry. During the growing season, net N mineralization rates were related to treatment effects on the soil micro-climate. High mineralization rates were found in the burned grapple piles, which were well-correlated to both high soil temperatures and water content, though also likely attributable to a post-burn nutrient pulse. Similarity between other treatments in net N transformation rates suggest that the availability of N is moderated both by C quantity and quality for microbial metabolism as well as treatment effects on the soil micro-climate.    Overland flow values for NO3, PO4, and SO4 were near levels found in rainfall chemistry for the northern Sierra.  Better understanding of changes in ecosystem processes following post-fire treatments will help managers meet post-wildfire restoration goals.