Disturbance regimes of hemlock-dominated old- growth forests in northern New York, U.S.A.

Old-growth forests often have complex, uneven age structures reflecting both the long time elapsed since a major disturbance and the periodic formation of small canopy gaps. I established 12 plots of 0.1 ha in four areas of old growth to describe the stand-scale disturbance regime of forests dominated by eastern hemlock (Tsuga canadensis (L.) Carriere) in northern Adirondack Park, N.Y., U.S.A. I analyzed radial-increment patterns of cores from all canopy trees (398 trees in total) on each plot to determine the date of accession to canopy for each tree. Major growth releases indicated disturbance events that resulted in either gap origin (16% of events) or release from suppression (82% of events). The average decadal rate of disturbance for all plots and decades of the 130-year period from 1850 to 1979 is 4.8–5.4% of current exposed crown area. The average canopy-tree residence time is 184–211 years. The stand-scale disturbance regimes in these Adirondack forests are similar to those of hemlock–hardwood fo...