Chronic Nitrogen Amendment Experiment at Harvard Forest since 1988

The purpose of this study is to increase our understanding of ecosystem nitrogen dynamics in response to elevated nitrogen inputs. With atmospheric nitrogen deposition in the Northeastern United States currently at 10 to 20 times above historic background levels, it is possible that excessive nitrogen inputs could saturate the retention capacity of a forest ecosystem. Potential effects of nitrogen saturation include increased nitrate leaching and simultaneous base cation losses, soil acidification, altered fluxes of trace gases and forest decline. Two adjacent stands were chosen for the study: an even-aged red pine (Pinus resinosa Ait.) stand planted in 1926 and a 50-year-old mixed hardwood stand that had regenerated naturally after clearcutting in approximately 1945. The hardwood stand is dominated by black and red oak (Quercus velutina Lam.; Q. rubra L.) with significant amounts of black birch (Betula lenta L.), red maple (Acer rubrum L.) and american beech (Fagus grandifolia Ehrh.). The dominant soil types are stony- to sandy-loams formed from glacial till, and are classified as Typic Dystrochrepts of the Canton or Montauk series. Four treated plots were established within each stand: control, low N, low N plus sulfur (N+S) and high N. Each plot measures 30 x 30 meters (0.09 ha) and is divided into thirty-six 5 x 5 m subplots.