A 300-YEAR HISTORY OF DISTURBANCE AND CANOPY RECRUITMENT FOR COOCCURRING WHITE-PINE AND HEMLOCK ON THE ALLEGHENY PLATEAU, USA

1 Dendroecological techniques were used to examine the patterns of can opy recruitment in relation to disturbance history for two dominant, y et ecologically contrasting, tree species, Pinus strobus (white pine; disturbance dependent) and Tsuga canadensis (hemlock; late successiona l), in a 300-year-old primary forest. 2 Most tree recruitment in both species occurred between 1690 and 1810. All of the white pine, which d ominated recruitment during the first 40 years due to more rapid heigh t growth, recruited in this period. Low levels of hemlock recruitment continued until 1900. Most of the younger trees comprised several nort hern hardwood species. No trees were less than 50 years old and the fo rest was devoid of an understorey due to intense deer browsing. 3 Radi al growth chronologies were determined for 27 cores across all species and age classes. These exhibited 1-11 major and/or moderate releases (indicative of disturbance) in most decades between 1730 and 1990. Pea k releases were recorded in the 1950s when a series of severe windstor ms impacted the site. Species recruitment patterns were related to ear lier growth releases observed in the oldest cores. 4 White pine exhibi ted a degree of plasticity in initial radial growth (1-5 mm year(-1)) depending on the time of establishment, as well as the ability to surv ive through prolonged periods of depressed growth (< 0.5 mm year(-1)) followed by growth releases. Hemlock was less plastic in its initial g rowth rates but did have dramatic growth releases (up to 8.8 mm year(- 1)) in several older trees. Thus, both species exhibited some unexpect ed dendroecological as well as successional attributes. 5 The future o f this stand is uncertain due to the impacts of deer and insect outbre aks that plague the region, as well as fortuitous natural disturbances , e.g. wind and fire. Nonetheless, the dendroecological approach eluci dated disturbance history, stand development and mechanisms of coexist ence of two ecologically contrasting tree species, and should be used to further understanding of the complex ecology of other mixed-species forests and the successional role of various tree species.