At the Harvard Forest Long-term Ecological Research Site Chronic Nitrogen Amendment Study, a red pine and a mixed deciduous stand showed immediate changes in soil respiration following nitrogen additions (low N: 5 g N m⁻² per year; high N: 15 g N m⁻² per year) during the initial year (1988) of the study. In the hardwood stand, soil respiration rates increased after N additions in the first year (control: 482.0 g C m⁻² per year; high N: 596.5 g C m⁻² per year). This increase is attributed to increased productivity in the hardwood stand compared to the pine stand; N additions are hypothesized to have increased either root or microbial activity, or perhaps both. In the second year, however, respiration in the fertilized hardwood plots was not different from the control plot. In the pine stand, annual soil respiration was 21 and 25% lower, respectively, in low N and high N plots than the control (429.9 g C m⁻² per year), with further reductions in the second year.