Revegetation and Nitrate Leaching from Lake States Northern Hardwood Forests Following Harvest

The sugar maple ( Acer saccharum Marshall)–red oak ( Quercus rubra L.) and sugar maple–basswood ( Tilia americana L.) ecosystems are Lake States forests that differ in net nitrification (5 and 15 g N m −2 yr −1 , respectively), but experience equivalent rates of NO − 3 leaching following clear‐cut harvest (≈5 g N m −2 yr −1 ). Our objectives were to determine whether high rates of N leaching are sustained following harvest and whether ecosystem‐specific patterns of biomass accumulation influence NO − 3 loss. We studied two stands in each ecosystem and established four research plots in each stand; two plots were clear‐cut in 1991 and two were controls. In 1996, we measured soil solution NO − 3 concentration (1‐m depth) and calculated areal losses by a water balance method. We used allometric equations to estimate woody biomass in clearcut plots; herbaceous biomass was clipped. In the sugar maple–red oak ecosystem, NO − 3 leaching from 5‐yr‐old clear‐cut plots (0.56 g N m −2 yr −1 ) was significantly greater than leaching from control plots (0.05 g N m −2 yr −1 ). In contrast, NO − 3 leaching did not differ between control (0.41 g N m −2 yr −1 ) and 5‐yr‐old clear‐cut (0.02 g N m −2 yr −1 ) in the sugar maple–basswood ecosystem; however, loss from these clear‐cut plots was significantly lower than that from clear‐cut sugar maple–red oak plots. Five years after harvest, 7.1 Mg ha −1 of aboveground biomass accumulated in clear‐cut sugar maple–basswood plots, almost twice that of clear‐cut sugar maple–red oak plots (3.9 Mg ha −1 ). Five years after harvest, the highest rates of NO − 3 loss occurred in the sugar maple–red oak ecosystem, in which aboveground biomass accumulation was least.