Susceptibility of Brewer Spruce (Picea breweriana) to Dwarf Mistletoes (Arceuthobiumspp., Viscaceae)

Abstract

Abstract Brewer spruce is an endemic of the Klamath and Siskiyou Mountains in southwestern Oregon and northwestern California. Three species of dwarf mistletoes (Arceuthobium spp.) have been reported to parasitize Brewer spruce, but the susceptibility of this spruce to infection by these parasitic plants has received no attention since the late 1960s. The objective of this study is to improve estimates of the susceptibility of Brewer spruce to these parasitic plants in select areas currently supporting highly infected dominant and co-dominant trees. Three mixed conifer stands infested with one of the three dwarf mistletoes known to infect Brewer spruce (nine stands total) were sampled to evaluate the relative susceptibility of this conifer to each mistletoe species. At each of the nine study sites, 10 to 20 temporary circular plots with a 6-m radius (0.012 ha) were established around large, severely infected trees. The following data were collected for each live tree within a plot: species, diameter, and ...