Dendroecology and successional status of two contrasting old-growth oak forests in the Blue Ridge Mountains, U.S.A.

Dendroecological techniques were used to investigate the dynamics and successional development spanning three centuries of two virgin, old-growth forests dominated by Quercus rubra L. (mesic site) and Quercus prinus L. (xeric site) on the Blue Ridge Mountains of west-central Virginia. In the Q. rubra stand, a large increase in recruitment of this species between 1820 and 1850 was associated with a sharp increase followed by a larger decrease in the master tree ring chronology. The decrease in growth between 1837 and 1844 coincided with a predicted southward displacement of the summertime position of the polar front from eastern Canada (E.R. Cook and P. Mayes. 1987. Decadal-scale patterns of climatic change over eastern North America inferred from tree rings. In Abrupt climatic change. Edited by W.H. Berger and L.D. Labeyrie. D. Reidel Publishing Company, Dordrecht, Holland. pp. 61-66). There was a virtual cessation of tree recruitment between 1850 and 1910, suggesting that the Q. rubra stand went through a 'midlife' stem exclusion stage. However, another period of peak recruitment between 1920 and 1940 coincided with chestnut blight (Endothia parasitica) and extreme drought 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 Q. rubra in this stand occurred between 1860 and 1950. There was also a trend of increasing growth in the oldest Q. 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 appears to represent an edaphic climax for this genus. The large increase of mixed-mesophytic species during the 1900s in the Q. rubra stand indicates its transitional nature in the absence of periodic fire.