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

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.

Landscape influences on stream fish assemblages across spatial scales in a northern Great Plains ecoregion

We examined the relationship between multiple spatial scales of fish assemblage structure and land cover in streams of a northern Great Plains ecoregion. We used regional richness measurements, an index of biotic integrity (IBI), and nonmetric multidimensional scaling (NMS) ordination to characterize fish assemblages. These metrics were related to regional catchment landscape at two spatial scales (overall catchment, overall riparian) and then to a set of local subcatchments from within these catchments at three scales (overall subcatchment, overall riparian buffer, and reach). Relationships between catchment fish richness, IBI scores, and landscape predictors were strongest at the riparian scale, with the strongest single predictor being riparian forest (r2 = 0.63, P < 0.01). NMS ordination analysis showed clear similarities between fish species assemblages in agriculturally dominated catchments and assemblages found in smaller headwater streams. At the same time, forested catchments and catchments with larger areas exhibited similar fish species assemblages. Our results indicate that both local and regional stream fish assemblages are structured by broader-scale landscape characteristics, with land cover providing a better indication of overall available habitat volume than catchment area or stream order.