This paper summarizes the accumulation of nutrient capital during the natural afforestation of iron-smelting slag. The study site was the Beckley Furnace (North Caanan, Connecticut, U.S.A.) slag dump, which was abandoned around 1918. Currently, a Pinus strobus (white pine)-dominated forest occupies the site. Our primary objective was to determine the relationships among stand development and belowground nutrient pools to evaluate controls on the rates at which nitrogen, calcium, magnesium, and potassium accumulate in the developing forest. Along a developmental gradient of increasing stand basal area, we measured (1) aboveground biomass, (2) root biomass, (3) above-ground nutrient capital, (4) belowground nutrient capital, (5) soil weight, (6) soil organic carbon weight, (7) soil moisture, and (8) understory richness and density. Regression analysis suggests, as expected, that the addition of organic matter controls the accumulation of above- and belowground nutrients, soil water, and understory plant composition and distribution. The rather rapid rate of nitrogen accumulation suggests that allochthonous as well as autochthonous organic matter is an important source of nutrients for the developing forest soil and vegetation. Compared to those of other northeastern forests, soils in the most developed areas at the Beckley site have accumulated more than enough labile nutrient capital in 75 years to support a forest typical of the region. In the most developed stands, understory composition indicates mesic soil conditions, and that within the next 75 years or so the Beckley slag dump will be floristically very similar to the surrounding forest.