Impacts of beech bark disease and deer browsing on the old-growth forest.
Old-growth stands within the Tionesta Research Natural Area were sampled in 1977, 1990 and 2000. Sapling growth within 25 treefall gaps was sampled all three times. Canopy trees were measured using the point-centered quarter method, with 83 points sampled all three times. Gap regeneration increased significantly in density and basal area from 1977-1990. Beech (Fagus grandifolia) significantly increased its relative gap sapling density from 68% to 91% to 94% over the 3 y. Other species decreased in absolute numbers presumably due to deer browsing. Canopy tree density remained constant and basal area increased 1977-1990 but both decreased 1990-2000. Species relative density and basal area values did not change. Mortality rates almost doubled from 1977-1990 to 1990-2000, increasing especially for smaller canopy trees. Snag densities and formation rates also increased, though not significantly, from the first to the second time interval. Beech, in particular, showed large increases in mortality, probably due to the growing impact of beech bark disease, which reached the stand about 1990. The stand seems changing to a new state with less beech in the canopy and more in the understory. Which species will replace beech in the canopy is difficult to predict.