TEMPORAL AND SPATIAL SHIFT WITHIN THE NECTRIA PATHOGEN COMPLEX-ASSOCIATED WITH BEECH BARK DISEASE OF FAGUS-GRANDIFOLIA

Beech bark disease occurs when either Nectria galligena Bres., or Nect ria coccinea var. faginata Lohman, Watson, and Ayers kills bark that i s or has been infested and altered by the beech scale, Cryptococcus fa gisuga (Lind.). Introduced to Nova Scotia around 1890, this insect now occurs as far southwest as Ohio, West Virginia, Virginia, and North C arolina. I determined the relative occurrence of the two pathogens in forests affected for varying times and the temporal changes in their r elative occurrence in recently affected stands of the Monongahela Nati onal Forest, West Virginia (MNF). Stands in the Canadian Maritimes, Ne w England, New York, and Pennsylvania were sampled in 1985-1986; and i n the Catskill Park, New York in 1988 and 1991. Stands on the MNF were sampled in 1982, 1983, 1984, 1986, 1988, and 1991. The following tren ds were indicated: N. galligena dominated recently affected stands in Pennsylvania and West Virginia, and N. coccinea var. faginata dominate d long-affected stands in Canada, New England, and New York. On the MN F, only N. galligena was isolated in 1982; by 1988, N. coccinea var. f aginata was isolated from 8 of 16 stands and from all 16 stands in 199 1. Stands where N. galligena persisted had higher proportions of tree species highly susceptible to N. galligena than stands dominated quick ly by N. coccinea var. faginata. Once present, however, N. coccinea va r. faginata eventually will replace N. galligena as the dominant patho gen.