Nitrogen (N) limitation was tested against other possible limiting factors (e.g. calcium, magnesium and or phosphorus limitation, aluminum toxicity) at a base-poor site receiving high rates of N deposition (approximately 12 kg ha^-1 yr^-1). Our objective was to quantify changes in understory productivity following additions of dolomite (9 Mg ha^-1), ammonium nitrate (25 kg N ha^-1 yr^-1) and phosphate (100 kg P ha^-1), and to compare the specific response of Acer saccharum, Dryopteris intermedia, Erythronium americanum, and Oxalis acetosella to the dolomite and ammonium nitrate treatments. We hypothesized that the greatest increases in understory productivity would occur with the dolomite + N treatment, but that the four study species would respond differently to the treatments. Specifically, Erythronium americanum would increase the most with the N treatment, while A. saccharum and O. acetosella would increase most with the dolomite + N treatments. The dolomite addition occurred in November of 2003 and N and P additions occurred in May of 2004. Over the following two summers we observed these trends: no significant differences between the treatments in total understory biomass, however summer-green herb density increased approximately three-fold with the dolomite + N treatment and was the only trend associated with the summer-greens that was different from zero. On average, tree seedlings increased by 33,000 stems ha^-1 with the dolomite + N treatment while on the control and N treatments, densities decreased by 4,000 and 44,000 stems ha^-1, respectively. Of the four study species, A. saccharum increased the most in relative growth rate on the dolomite + N treatment. Increases in A. saccharum growth rate were significantly and positively correlated with calcium, magnesium and pH in the Oe horizon, while increases in E. americanum growth rate were significantly and positively correlated with exchangeable aluminum and organic matter in the B horizon. On the dolomite + N treatment, A. saccharum increased in whole-plant Mg:Al by a factor of seven relative to the control, and E. americanum increased in aluminum by a factor of two to three relative to the control across all other treatments. In sum these data show that generalizations regarding nitrogen saturation of this understory plant community are uncertain as species are responding differently to environmental gradients, and that once Ca or Mg needs are met, additional N inputs appear to facilitate increased production.