Understory plant community response to nitrogen and dolomite additions in a northern hardwood forest of the Catskill Mountains, New York

The purpose of this study was to assess current nutrient limitations in understory vegetation of a northern hardwood forest in the Catskill Mountains of New York receiving high rates of nitrogen deposition (9-12.5 kg N ha -1 yr-1). Four species of interest (Dryopteris intermedia, Oxalis acetosella, Erythronium americanum and Acer saccharum) were monitored in permanent plots for one year before and three years after application of ammonium nitrate (25 kg N ha-1 yr-1) and dolomite (5.5 tons ha-1 CaCO 3 and 4.1 tons ha-1 MgCO3). Two years following treatment application (2005), increases in pH and calcium and magnesium concentrations were observed in the soil organic horizons of dolomite plots. Three years following treatment application (2006), there were no significant treatment responses of Dryopteris intermedia biomass over time. However, Oxalis acetosella exhibited higher relative growth rates in the dolomite and dolomite plus nitrogen treatments as compared to the control, which corresponded to higher tissue concentrations of calcium and magnesium. Erythronium americanum exhibited increased growth following both dolomite and nitrogen additions, possibly resulting from increased magnesium nutrition. Finally, Acer saccharum exhibited higher germination and survival rates in the dolomite treatments during the first two years following treatment application (2004 and 2005), as compared to the control, which corresponded to higher foliar calcium and magnesium concentrations. Since some species within the understory responded positively to nitrogen addition, there is not enough evidence to conclude that this stratum of the forest is nitrogen saturated.;Keywords. understory, northern hardwood forest, nitrogen saturation, liming, nitrogen deposition, Dryopteris intermedia, Oxalis acetosella, Erythronium americanum, Acer saccharum...