A/V A/P P/C 



HABITAT TYPE 



Figure 2. --Relative intensity of mountain pine beetle tree killing and duarfmistletoe 

 infection on three habitat types. A/V = Abies lasiocarpa/Vaccinium scoparium; A/P = 

 Abies lasiocarpa/Pachistima myrsinites; and P/C = Pseudotsuga menziesii/Calamagrostis 

 rubes cens . 



Intensity indexes for both beetle infestation and dwarfmistletoe infection were 

 calculated as weighted indexes. The relative indexes derived simplify the comparisons 

 by transforming the data to comparable units. 



The higher elevation stands represented by the Abies lasiocarpa/Vaccinium scoparium 

 habitat type show the lowest index of mountain pine beetle infestation as illustrated in 

 figure 2. At the same time, these stands sustain the highest index of dwarfmistletoe 

 infection. Whether or not this inverse relationship has biological meaning is largely 

 unknown. However, the relationship is relevant if the ability of the mountain pine 

 beetle to produce sufficient brood to sustain an infestation is related significantly 

 to the thickness of the phloem layer. A small sample of 20 randomly selected trees 

 taken in a lodgepole pine stand on the Moose Creek Plateau, Targhee National Forest, 

 suggests that the thickness of the phloem in lodgepole pine trees is significantly 

 reduced in trees moderately to heavily infected by dwarfmistletoe. The results are 

 tabulated as follows: 



Level of dwarfmistletoe 



infection Radial thickness of phloem 



(Inches) 



No infection 0.170 ±0.0213 P = 0.95 



Medium to heavy infection 0.112 ±0.0218 P = 0.95 



A high proportion of the trees in the sampled area would not be suitable for sustain- 

 ing an infestation if we assume that a radial phloem thickness of about 0.12 inch is 

 needed. 



6 



