Tree dynamics in an old-growth, deciduous forest

Abstract

In 1926, all trees (⩾ 10.2 cm dbh) were measured, tagged and mapped in a 20.6 ha, old-growth oak forest within the extensively farmed Tipton Till Plain of Indiana. All trees (⩾ 10.0 cm dbh) within the central 8.5 ha of this forest were measured, tagged and mapped again in 1976. Stand density and basal area increased by 93.9 and 30.8%, respectively, to 320 stems ha −1 and 31.0 m 2 ha −1. Density of Ulmus americana and Acer saccharum increased most; the largest density decreases were of Quercus rubra and Fraxinus americana. Basal area increases were greatest for Q. rubra, A. saccharum, and Q. alba. The most important species in 1926 were (in order of decreasing importance value, IV) [IV = (relative density + relative basal area)/2] Q. rubra, F. americana, Q. alba, Q. macrocarpa and U. americana. In 1976, Q. rubra, U. americana, A. saccharum, Q. alba and F. americana were the most important. Nearly half (46.9%) of those trees measured in 1926 had died by 1976; however, mortality varied by species, size-class and size-class within a species. Species with low mortality (⩽ 25%) included A. saccharum, Aesculus glabra, Carya spp. (except C. cordiformis), Celtis occidentalis and Quercus spp. (except Q. rubra). Species with high mortality (⩾ 75%) included Fagus grandifolia, Ulmus americana, U. rubra, and Fraxinus nigra. The majority of ingrowth trees within a 5 m radius gap of dead dominant or codominant trees were U. americana (30% of total), followed by A. saccharum (20%). No species had greater than 50% of its ingrowth within a 5 m radius of the dead trees. Diameter growth of surviving trees varied greatly among species, size-class and size-class within a species. Q. rubra and F. americana had greatest average diameter increases after 50 years (21.8 and 18.4 cm dbh, respectively). Mortality was relatively low and diameter growth high in the 50.0–69.9 cm diameter class for all species combined. The rotated-sigmoid curve, rather than the negative exponential, appears to best describe the size-class distributions of all species in 1976. An analysis of the size-class distribution of all species suggests that early and mid-seral species such as Gleditsia triacanthos, Juglans nigra, and Quercus spp. are gradually being replaced by more tolerant, late seral and climax species such as Acer saccharum, Aesculus glabra, Carya ovata and others. Despite the old-growth appearance of this forest much structural and compositional changes have been taking place.