Disturbance history and climate response in an old-growth hemlock-white pine forest, central Pennsylvania

Radial growth patterns are examined in relation to the historical development, disturbance history, and climate responses of an old-growth hemlock forest located in central Pennsylvania. Hemlock recruited continuously from the mid 1700s through 1890 with a sharp pulse of regeneration between 1860 and 1870, while white pine formed an even-aged cohort in a narrow interval between 1865 and 1870. No recruitment of any species occurred in the 20^th century, likely because of deer browsing. Isolated pulses in radial growth occurred in almost every decade of the chronology, indicating a high frequency of small-scale disturbances. Major stand-wide pulses in hemlock radial growth occurred around 1810 and 1850. The 1850 event corresponds with the date of two intense windstorms and was the only disturbance event large enough to recruit white pine. Long-term effects of climate were apparent in the 20^th century in which periods of low radial growth occurred in the cool, dry periods of 1910-1930 and 1965-1970. Correlations and response function analysis revealed that hemlock radial growth was limited by drought in winter and early fall, and by low March temperatures.