Early-successional dynamics of single-aged mixed hardwood stands in a southern New England forest, USA

The pattern of stand development was studied in two mixed-species single-ag ed stands that originated after true clearcutting at the Great Mountain For est in northwestern Connecticut. One stand was located on a mesic swale-til l site and the other on a more xeric thin-till site. At the time of cutting all sprout growth and advanced regeneration was eradicated, except for 1-y ear-old red oak (Quercus rubra) seedlings. Twenty-eight years after the sta nds originated trees were stratified by shade tolerance such that the canop ies were dominated by the intolerant species (paper birch Betula papyrifera , gray birch B. populifolia, pin cherry Prunus pensylvanica) with mid-toler ant species (black birch B. lenta, black cherry P. serotina) becoming preva lent. The number of stems was decreasing but the basal area was steadily in creasing. The pattern in species-specific growth rates and crown position w ere common to both sites; but there: were also differences between the site s in the sizes of trees and positioning of the mid-tolerant trees in the ca nopy. At age 28 the more mesic swale-till site had fewer, taller trees, wit h pioneer species more typical of northern hardwood climates. On this site red oak was doing poorly, all gray birch and eastern white pine (Pinus stro bus) had died, black birch and black cherry were beginning to dominate the canopy of the stand, and a significant understory of beech (Fagus grandifol ia) had developed through the encroachment of root suckers from the stand e dge. Sugar maple (Acei saccharum), white ash (Fraxinus americana) and easte rn hemlock (Tsuga canadensis), all significant components of the swale-till site before clearcutting, were noticeably absent. On the thin-till site re d oak had not attained the canopy of the stand but was still a significant component of the mid-story with red maple (A. rubrum). However, black birch was self-thinning more rapidly on the thin-till site than that of the swal e-till suggesting that red oak and red maple might well dominate the canopy within another 20 years. In general, the diameter growth rate of the thin- till site currently lags behind the swale-till by approximately 10 years. ( C) 1999 Elsevier Science B.V. All rights reserved.