Structure, radial growth dynamics and recent climatic variations of a 320-year-old Pinus rigida rock outcrop community.

Abstract

The composition, structure and dendroecology of a 320-year-old Pinus rigida rock outcrop community was studied in the Shawangunk Mountains of southeastern New York. This represents one of the oldest known examples of this forest type and it is located on one of the most extreme sites in the northeastern United States. P. rigida represented 88% of all sampled trees, which typically grew on individual soil islands with soil depths of 8-35 cm surrounded by exposed bedrock. The forest was uneven-aged and P. rigida exhibited continuous recruitment into the tree size classes since the late 1600s, suggesting that it represents a physiographic climax for this species. However, a limited amount of Nyssa sylvatica and Quercus prinus recruitment started after 1830. Peak recruitment of P. rigida trees in 1720-1760 and 1860-1890 coincided with parabolic-shaped releases in their radial growth, possibly in response to disturbances. Tree ring growth was typically <0.4 mm/year since the 1850s and <0.3 mm/year during a prolonged and severe drought in the 1960s. However, large increases in precipitation and temperature from 1970 to 1993 were correlated with a dramatic post-drought growth response producing the highest ring width index values throughout the life of 260 to 280-year-old trees. Thus, we attribute certain moderate growth releases (>50%) lasting 10-15 years to climate, rather than disturbance. Tree growth and recruitment at the study site were influenced by a complex interaction of climate, soil and disturbance factors. Coupling of species recruitment, tree ring and climatic data in this study provided an improved technique for understanding forest growth and dynamics.