Forest Insect Resegirch 



Effects of black-headed budworm feeding on second-grovrth 



In order to determine the nature and amount of budworm damage to second- 

 growth hemlock and spruce, detailed investigations were made on two areas 

 in the vicinity of Juneau. Defoliation on these areas differed fran the 

 us\:ial pattern in that there was no subsequent budworm feeding after the 

 fir*3t year. While budworm damage on these areas is fairly representative 

 of average conditions, it must be stressed that some stands of second-growth 

 suffered much greater destruction and, of course, many yoimg stands s\is- 

 tained little damage. 



Budworm damage to second-growth western hemlock 



In the fall of 1952, the black-headed budworm deposited an average of 2.3 

 eggs per normal twig-inch of foliage in the upper crowns of second-growth 

 hemlock trees. Using this measure as a guide to the relative abundance of 

 the budworm, larval defoliation and damage on a nearby stand of pure hemlock 

 second-growth was measured. 



The two and one-half -acre stand of hemlock second-growth originated from a 

 clearcutting in or about 1924. Reproduction came in thick and in 1954 there 

 were still 3220 hemlock and 100 spruce per acre in trees one inch DBH and 

 larger. The dominant hemlock averaged 27 feet in height and 4 inches in 

 diameter at breast height. The investigation of budworm damage, all of which 

 occTorred in 1953> was carried out on a one-tenth-acre plot within the stand 

 of second-growth hemlock. The trees on the plot were arbitrarily set down 

 in one of four crown classes in an attempt to show their relative size and 

 the relation of size to budworm damage. 



Damage data collected in 1954 on this plot show that budworm feeding in 

 1953 caused top kill in 25 percent of all hemlock stems. By crown class 

 the percentages were: doninant - 85 percent; codominant - 52 percent; 

 intermediate - 10 percent; overtopped - 1 percent. Length of this top kill 

 averaged 2 feet for doninant hemlock (range 0*0" to 6*6'*); 1 i'oot for co- 

 dominant hemlock (range 0*0*' to 4*8"); 1 inch for intermediate hemlock 

 (range 0*0" to 2*2"); and ,2" for overtopped hemlock (range 0*0" to 1*11"). 



Complete top defoliation occurred on 40 percent of a.11 hemlock stems. By 

 crown class the percentages were: doninant - 95 percent; codoninant - 91 

 percent; intermediate - 31 percent; overtopped - 6 percent. Length of 

 complete top defoliation averaged 6*8?' for dominant trees (range 0*0" to 

 14*0"); 3*10" for codominant trees (range 0*0" to 9*0"); 1*0" for inter- 

 mediate trees (range 0*0" to 8*0"); and 2" for overtopped trees (range 

 0*0" to 5*0"). 



The few Sitka spruce trees on the plot, most of which are overtopped trees, 

 showed no evidence of budworm damage. 



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