Spread, Intensification, and Upward Advance of Dwarf Mistletoe in Thinned, Young Stands of Western Hemlock in Southeast Alaska

Abstract

Examinations of 206 young western hemlock trees growing beneath residual trees infected with hemlock dwarf mistletoe (Arceuthobium tsugense) in two thinned stands were made from 1981 to 1987 to evaluate disease spread and intensification. The percentage of trees infected increased over this period, as did the number of infections on 79% of the trees that were infected in 1981. However, few of the infected trees had three or more infections and only eight trees had 10 or more infections by 1987. The probability of a tree being infected was significantly greater if the tree was in the understory before logging rather than having become established in the understory after logging. There was no significant orientation by distance or direction of infected trees from the infected residual trees (.)