DENDROECOLOGY AND SUCCESSIONAL STATUS OF 2 CONTRASTING OLD-GROWTH OAKFORESTS IN THE BLUE-RIDGE MOUNTAINS, USA

Dendroecological techniques were used to investigate the dynamics and successional development spanning three centuries of two virgin, old-g rowth forests dominated by Quercus rubra L. (mesic site) and Quercus p rinus L. (xeric site) on the Blue Ridge Mountains of west-central Virg inia. In the e. rubra stand, a large increase in recruitment of this s pecies between 1820 and 1850 was associated with a sharp increase foll owed by a larger decrease in the master tree ring chronology. The decr ease in growth between 1837 and 1844 coincided with a predicted southw ard displacement of the summertime position of the polar front from ea stern Canada (E.R. Cook and P. Mayes. 1987. Decadal-scale patterns of climatic change over eastern North America inferred from tree rings. I n Abrupt climatic change. Edited by W.H. Berger and L.D. Labeyrie. D. Reidel Publishing Company, Dordrecht, Holland. pp. 61-65). There was a virtual cessation of tree recruitment between 1850 and 1910, suggesti ng that the Q. rubra stand went through a ''midlife'' stem exclusion s tage. However, another period of peak recruitment between 1920 and 194 0 coincided with chestnut blight (Endothia parasitica) and extreme dro ught in the region. Oak recruitment in the Q. prinus stand was fairly continuous and exhibited peaks from 1710 to 1730 and in the 1940s that were associated with releases in radial growth. An increase in e. rub ra in this stand occurred between 1860 and 1950. There was also a tren d of increasing growth in the oldest e. prinus trees from 1860 to the present, particularly between 1930 and 1960. The xeric Q. prinus stand had only a small component of potential oak replacement species and a ppears to represent an edaphic climax for this genus. The large increa se of mixed-mesophytic species during the 1900s in the e. rubra stand indicates its transitional nature in the absence of periodic fire.