STRUCTURE, RADIAL GROWTH DYNAMICS AND RECENT CLIMATIC VARIATIONS OF A320-YEAR-OLD PINUS-RIGIDA ROCK OUTCROP COMMUNITY

The composition, structure and dendroecology of a 320-year-old Pinus r igida rock outcrop community was studied in the Shawangunk Mountains o f southeastern New York. This represents one of the oldest known examp les of this forest type and it is located on one of the most extreme s ites in the northeastern United States. P. rigida represented 88% of a ll 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 tr ee size classes since the late 1600s, suggesting that it represents a physiographic climax for this species. However, a limited amount of Ny ssa sylvatica and Quercus prinus recruitment started after 1830. Peak recruitment of P. rigida trees in 1720-1760 and 1860-1890 coincided wi th parabolic-shaped releases in their radial growth, possibly in respo nse to disturbances. Tree ring growth was typically < 0.4 mm/year sinc e 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 d isturbance. Tree growth and recruitment at the study site were influen ced 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 a nd dynamics.