Soil nitrogen mineralization and enzymatic activities in fire and fire surrogate treatments in California

Abstract

Miesel, J. R., Boerner, R. E. J. and Skinner, C. N. 2011. Soil nitrogen mineralization and enzymatic activities in fire and fire surrogate treatments in California. Can. J. Soil Sci. 91: 935–946. Forest thinning and prescribed fire are management strategies used to reduce hazardous fuel loads and catastrophic wildfires in western mixed-conifer forests. We evaluated effects of thinning (Thin) and prescribed fire (Burn), alone and in combination (Thin+Burn), on N transformations and microbial enzyme activities relative to an untreated control (Control) at 1 and 3 yr following treatment in northern California. N mineralization and net nitrification were reduced by Thin and by Burn in year 1, and N mineralization was increased by Thin+Burn in year 3, relative to the Control. In general, all experimental treatments reduced soil enzyme activity. To identify overall treatment effects on the below-ground ecosystem, we combined these data with soil physicochemical data from this site to perform non-metric multidimensional scaling (NMS) ordination. NMS ordination showed that Burn and Thin+Burn produced the greatest overall effects on soil, and that overall differences in soil characteristics among treatments diminish over time. These results provide an important benchmark for monitoring ecosystem effects of large-scale wildfire hazard reduction strategies over the long term.