In 1930-32 Carl Heimburger sampled soils at >100 locations in the Adirondack Mountains of New York. In 1984 we sampled soils at 48 sites located in spruce/fir, northern hardwood and pine-dominated stands and established permanent vegetation plots at those sites to track changes in vegetation and soil chemical properties. The 1932-1984 comparisons indicated that at a high proportion of the sites, pH and extractable Ca decreased. Calcium loss from the soil accelerated by acid deposition is thought by some to be a factor in red spruce and sugar maple decline diseases, hypotheses that can tested by comparing changes in vegetation and soil acid-base status. We remeasured trees in the permanent plots and sampled O horizons at 39 sites in 2004. Over the past 20 yr, live red spruce and sugar maple basal area (BA) decreased by 40% and 13% respectively (P<.05). The live BA of the spruce-fir and northern hardwood plots decreased (P<.05) while the BA of pine-dominated plots increased 18% (P<.05). The pH of O horizons in the spruce/fir plots increased (P<.05), did not change in the northern hardwood plots, and decreased in the pine plots (P<.05). Extractable Ca increased (P<.05) in the Oa horizons of spruce/fir plots, did not change in the northern hardwood plots and decreased (P<.05) in the O horizons of pine-dominated plots. We hypothesize that among the important factors governing the changes in soil chemistry are Ca release from dead red spruce wood which accumulated in the spruce/fir plots since the 1960's, and sequestration of Ca by rapidly growing trees in the pine-dominated stands.