Two decades of change in vegetation in Adirondack spruce-fir, northern hardwood and pine-dominated forests1

In 2004 we remeasured trees in 42 permanent vegetation plots that had been established in Adirondack spruce-fir, northern hardwood, and pine-dominated stands in 1984. Over the 20-yr interval, live basal area (BA) in red spruce and/or balsam fir-dominated plots decreased by 15%. Blowdown was a major cause of balsam fir, but not red spruce mortality in two plots. Excluding the two blowdown plots, balsam fir live BA increased by 17%, while red spruce live BA decreased by 42% (P < 0.05). There was no significant change in the overall live BA of northern hardwood plots. However, excluding beech, the pooled northern hardwoods showed a significant decrease (P ≤ 0.05) in live BA over the 20-yr interval. In contrast to the spruce-fir and northern hardwood plots, the live BA of pine-dominated plots increased by 19% over the 20-yr interval (P ≤ 0.01). Changes in sapling densities in the spruce/fir plots were not significant, though fir in the 2–9.9 cm dbh class reached densities of > 3000 stems ha−1 in four plots where they filled large gaps. There was a trend toward increased red spruce sapling density (P ≤ 0.10) in the upper northern hardwood zone (600–950 m). Sugar maple sapling density and BA decreased significantly (P ≤ 0.05) in the northern hardwood plots during the twenty-year interval.