The relationship of Douglas-fir dwarf mistletoe (Arceuthobium douglasii) to stand conditions and plant associations in the southern Cascade Mountains, Oregon
Filip, Gregory M.
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Douglas-fir dwarf mistletoe (Arceuthobium douglasii) is a parasitic plant widely distributed on Douglas-fir (Pseudotsuga menziesii) in southwestern Oregon. This study examined the relationship of frequency of occurrence and severity of Douglas-fir dwarf mistletoe with stand conditions and plant associations in the southern Cascade Mountains in Oregon. Data were collected from a subsample of existing permanent plots. Fifteen stand variables and the level of dwarf mistletoe infection in all live Douglas-fir were measured at each plot. Douglas-fir dwarf mistletoe occurred most frequently in the white fir (Abies concolor) series. It occurred least in the Douglas-fir series. It occurred in plots at significantly higher elevations, with lower mean annual temperatures and lower mean annual and dry season precipitation than plots where it was absent. Occurrence of Douglas-fir dwarf mistletoe was also significantly associated with steeper slopes, andesite and basalt soil parent materials, lower basal area, and lower percentage of Douglas-fir in the stand. The average plot Dwarf Mistletoe Rating did not differ significantly among climax series. Average plot Dwarf Mistletoe Rating did increase significantly as total basal area decreased and age of the oldest canopy layer increased. Our study suggests that climax series could be used as indicators of the relative frequency of Douglas-fir dwarf mistletoe in the southern Cascade Mountains in Oregon