The dendroecology and climatic impacts for old-growth white pine and hemlock on the extreme slopes of the Berkshire Hills, Massachusetts, USA

Dendrochronological techniques were used to investigate the dynamics of an old-growth forest on the extreme slope (65%) at Ice Glen Natural Area in so uthwestern Massachusetts. The site represented a rare opportunity to study the disturbance history, successional development, and responses to climati c variation of an old-growth hemlock (Tsuga canadensis (L.) Carr) - white p ine (Pinus strobus L.) - northern hardwood forest in the northeastern Unite d States. Hemlock is the oldest species in the forest, with maximum tree ag es of 305-321 years. The maximum ages for white pine and several hardwood s pecies are 170-200 years. There was continuous recruitment of hemlock trees from 1677 to 1948. All of the existing white pine was recruited in the per iod between 1800 and 1880, forming an unevenly aged population within an un evenly aged, old-growth hemlock canopy. This was associated with large incr eases in the Master tree-ring chronologies, indicative of major stand-wide disturbances, for both hemlock and white pine. Nearly all of the hardwood s pecies were also recruited between 1800 and 1880. After 1900, there was a d ramatic decline in recruitment for all species, including hemlock, probably as a result of intensive deer browsing. White pine and hemlock tree-ring g rowth during the 20th century was positively correlated with the annual Pal mer drought severity index (r = 0.61 and 0.39, respectively). This included reduced growth during periods of low Palmer drought severity index values, the drought years of 1895-1922, and dramatic increases during periods of h igh Palmer drought severity index values in the 1970s and 1990s. Significan t positive and negative correlations of certain monthly Palmer drought seve rity index values with 20th century tree-ring chronologies also exist for w hite pine and hemlock using response function analysis. The results of this study suggest that old-growth forests on extreme sites in the eastern Unit ed States may be particularly sensitive to direct and indirect allogenic fa ctors and climatic variations and represent an important resource for study ing long-term ecological and climatic history.