This variation is most likely due to a history of 

 complex, mixed-severity fire regimes in these 

 forests. Such fires would leave both 

 mistletoe-infected and noninfected trees to 

 provide seed for the next generation. 

 Depending on the spatial distribution of the 

 infected, mature trees, the regeneration 

 might: 1 ) remain free of infection, 2) have a 

 substantial lag time prior to infection, or 3) 

 become infected early in development. The 

 earlier a tree becomes infected by dwarf 

 mistletoe, the greater the impacts. 



Severity of mistletoe infection is most 

 commonly based on the Hawksworth dwarf 

 mistletoe rating (dmr), in which the live crown 

 of each tree is divided into thirds and rated 

 individually for presence and amount of 

 infection {Hawksworth 1977). The scores for 

 each third (0 = no infection; 1 = less than 50 

 percent of branches infected; 2 = greater than 

 or equal to 50 percent of branches infected) 

 are then added together. A Hawksworth dmr 

 of designates an uninfected tree, a dmr of 1 

 to 2 is considered a "light" infection, a dmr of 

 3 to 4 is considered a "moderate" infection, 

 and a dmr of 5 to 6 is considered a "severe" 

 infection. 



Due to the seeding habit of dwarf mistletoe, 

 spread and intensification are at their worst 

 ' when an infected overstory exists over 

 regeneration of the same tree species. 

 J Removal of the most severely infected trees 

 in these stands would be a way to salvage 

 recent and near-future mortality in severely 

 infected western larch, as well as to take the 

 first step in a silvicultural strategy to promote 

 vigorous, non- or lightly-infected western 

 larch regeneration in these stands. 



• I'tatheadedfir borer 



Wood borers are not generally considered 

 primary mortality factors of healthy, vigorous 

 trees. Instead, they very commonly attack 

 trees that have been weakened or recently 

 killed by other causes, such as fire, disease, 

 or bark beetle attack. However, the 

 flatheaded fir borer is capable of killing 

 seemingly healthy trees growing on dry sites 

 or affected by severe drought. Over the last 

 several years in northwest Montana, a 

 seemingly abnormal amount of mortality has 

 been observed in western larch, and a recent 

 '; report has implicated the flatheaded borer in 



much of the mortality {Gibson 2004). 

 Western larch is one of the hosts for 

 flatheaded fir borer, and drought and/or dwarf 

 mistletoe infection are considered 

 predisposing factors for attack. However, as 

 Gibson (2004) pointed out, as long as a 

 drought persists, there is little that can be 

 done to mitigate the damage by the 

 flatheaded fir borer. 



Doiigltvt-fir beetle 



Douglas-fir bark beetle is a native, common, 

 and potentially very damaging bark beetle of 

 Douglas-fir in the Northern Rocky Mountains 

 {Schmitz and Gibson 1996). Mortality due to 

 Douglas-fir bark beetle usually occurs in 

 small groups within dense, mature stands of 

 Douglas-fir, but during outbreaks of Douglas- 

 fir bark beetle, 100-tree groups are not 

 uncommon. The first indication of successful 

 attack by Douglas-fir bark beetle in the spring 

 and early summer is an accumulation of 

 reddish-orange frass, produced as beetles 

 bore into the inner bark of the tree, in bark 

 crevices up and down the stem, and at the 

 base of the tree. Due to wind and rain, the 

 frass may be dispersed over the course of the 

 summer, so close inspections are required 

 when examining trees with green foliage in 

 the late summer or fail for evidence of 

 attacks. Numerous long, clear, narrow pitch 

 streamers may be seen coming from well up 

 the bole of Douglas-fir bark beetle-attacked 

 trees, but these are not consistently present. 

 Attacks by bark beetles are generally 

 concentrated at the mid-bole of trees, so 

 evidence of current attacks, such as frass 

 and beetle galleries underneath the bark, are 

 not always readily visible at eye-level. 



The Douglas-fir bark beetle has one 

 generation per year, with broods 

 overwintering mostly as adults. Adult 

 emergence and flight occurs from late April to 

 early May, depending on temperature and 

 elevation. Dispersing adults seek out and 

 attack suitable hosts, mate, and lay eggs, 

 thereby producing the next generation of 

 beetles. Foliage of trees that were 

 successfully attacked in the spring can start 

 turning color by August of the same year, but, 

 depending on various factors, can remain 

 green till the following spring or early 

 summer. Therefore, Douglas-fir bark beetle 

 brood trees, or those containing overwintering 



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Forest Insect and Disease Report 



