Growth decline in red spruce and balsam fir relative to natural processes

Average annual growth of 3,001 red spruce (Picea rubens Sarg.) trees on plots randomly located across northern New England and upstate New York shows a regionally consistent decline starting soon after 1960. Depending on location, basal-area increment in 1980 was 13 to 40% less than in the peak growth year around 1960. The growth decline occurs in all size and age classes and is independent of elevation. Balsam fir (Abies balsamea (L.) Mill.) also shows a growth decline, but the start varies by tree age. The growth decline in both species is explainable at least in part by natural growth processes, complicating the task of evaluating the effects of atmospheric deposition.