Revegetation and nitrate leaching from Lake States northern hardwood forests following harvest

The sugar maple (Acer saccharum Marshall)-red oak (Quercus rubra L.) and su gar 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, leaching following clear-cut harves t (approximate to 5 g N m(-2) yr(-1)). Our objectives were to determine whe ther high rates of N leaching are sustained following harvest and whether e cosystem-specific patterns of biomass accumulation influence NO3- 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 199 6, we measured soil solution NO3- concentration (1-m depth) and calculated areal losses by a mater balance method. We used allometric equations to est imate woody biomass in clear-cut plots; herbaceous biomass was clipped. In the sugar maple-red oak ecosystem, NO3- leaching from 5-yr-old clear-cut pl ots (0.56 g N m(-2) yr(-1)),,, significantly greater than leaching from con trol plots (0.05 g N m(-2) yr(-1)). In contrast, NO3- leaching did not diff er 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 th ese clear-cut plots was significantly lower than that from clear-rut sugar maple-red oak plots. Five Sears 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 aft er harvest, the highest rates of NO3- loss occurred in the sugar maple-red oak ecosystem, in which aboveground biomass accumulation tvas least.