Basal area growth impacts of dwarf misletoe on western hemlock in an old-growth forest

Abstract

We investigated the effect of western hemlock dwarf mistletoe (Arceuthobium tsugense (Rosend.) G.N. Jones ssp. tsugense) on the 13-year basal area growth of large (>45.7 cm diameter at breast height) western hemlock (Tsuga heterophylla (Raf.) Sarg.) trees in an old-growth forest in southwestern Washington state. We controlled for spatial effects on tree growth by using twenty-seven 0.4-ha plots that had uninfected, lightly, moderately, and severely infected classes of trees present on each plot. Basal area growth was analyzed using analysis of covariance of a randomized block design that was a balanced design with four treatments (infection classes) and 27 replicates (blocks or 0.4-ha plots), with initial diameter as the covariate. Basal area growth was found to be significantly different among the infection classes (F_[3.77] = 10.09 and p < 0.0001). Growth of the light and moderate infection classes was not detectably different from growth of uninfected trees. However, severely infected trees grew from 16 to 46 percent (mean = 36 percent) less than uninfected trees of the same initial diameter over the period of study (1991-2004). The large trees in this stand did not show growth impacts until they were severely infected.

Citation

Shaw, David C.; Manuela, Huso; Bruner, Howard. 2008. Basal area growth impacts of dwarf misletoe on western hemlock in an old-growth forest. Canadian Journal of Forest Research. 38: 576-583