The temporal variation in species recruitment was examined in relation to annual dendrochronological data to determine the historical development and disturbance history of an old-growth bottomland hemlock-hardwood forest in the Cook Forest State Park in Northwestern Pennsylvania. This 15 ha forest, located at the headwaters of a stream, contains a mixture of Tsuga canadensis (hemlock), Fagus grandifolia (beech), Quercus rubra (northern red oak), Pinus strobus (white pine), and Acer rubrum (red maple). The present age structure indicates that a cohort of Quercus alba (white oak) established between 1680 and 1710, and that the oldest hemlocks became established in the early 1700s. A period of almost 100 years followed in which there was virtually no recruitment. Tree recruitment resumed about 1800 and consisted primarily of hemlock and beech until 1855. A period of episodic recruitment associated with a concomitant radial growth increase, indicative of a major disturbance, began in many of the oldest trees in the stand during the 1850s and persisted for 70 years. Approximately two-thirds of all trees aged in this study became established between 1855 and 1930. The presence of decayed, cut stumps of several different species scattered throughout the stand is evidence that selective logging occurred, probably during the middle to late 1800s. This activity greatly altered the structure and composition of the forest and created conditions favorable for the establishment of even-aged cohorts of relatively shade intolerant Q. rubra and P. strobus, not recorded in the stand prior to cutting, as well as cohorts of late-successional tree species. In response to canopy closure and a large increase in deer populations, few new trees were recruited since 1930. Therefore, this forest has experienced dramatic changes following Euro-American settlement of the region that continue to the present, despite the fact that it retains many old-growth characteristics. This study represented a rare opportunity to investigate the impacts of direct and indirect anthropogenic influences on an old-growth forest. The results are relevant for the restoration ecology of other eastern forests, because they point out that certain silvicultural techniques may differ broadly from natural disturbances and result in unique and uncharacteristically diverse assemblages of species.
All Science Journal Classification (ASJC) codes
- Ecology, Evolution, Behavior and Systematics
- Plant Science