Biochar application in forest soils can influence tree growth and forest productivity through mediating plant-available nitrogen (N) pools. However, how soil N availability and related transformations respond to biochar addition in cold-temperate forest ecosystems is not well understood. Our study assessed the effect of a hardwood forest residue biochar on soils taken from an elevational gradient within a cold-temperate, north Idaho forest. Forest soils were incubated at 0%, 10% and 20% biochar amendments in a greenhouse for 120 days. We measured soil small organic N (amino compound) and inorganic N (ammonium and nitrate) pools, enzyme activities, small organic N turnover, N mineralization and nitrification rates. Biochar decreased small organic N and inorganic N concentrations in most elevations. Enzyme analysis shows biochar increased the activity of aminopeptidase, but decreased the activity of N-acetyl-β-d-glucosaminidase, β-glucosidase and acid phosphatase. Biochar did not influence small organic N turnover and N mineralization rates, but decreased nitrification rate. In conclusion, hardwood forest residue biochar application in cold-temperate forests has important impact on short-term soil N cycling.