Wind breakage, sooty bark canker, and "barking" complemented by weak parasites and 

 stem-boring insects accounted for most of the aspen mortality on the sample plots, as 

 shown in the following tabulation: 



Size class 

 in. d.b.h. 



Wind breakage 

 Percent 



Sooty bark canker 

 Percent 



"Barking, " weak 

 parasites, pests, etc . 

 Percent 



0.1-6.0 

 6.1-12.0 

 12.1-18.0 



1 



8 

 25 



28 

 73 

 75 



71 

 19 

 



Combined 



35 



63 



Death resulting from wind breakage or windfall was infrequent in small trees but 

 rather common in the larger tree classes. 



Cenangium singulare, cause of sooty bark canker, was the single most injurious pathogen 

 found on dead trees (fig. 5), and it too was especially prevalent in the larger tree 

 classes. The third group was composed of trees that seemed to have died from a mixture 

 of the following: bark wounding by elk or moose; infestation by stem-boring insects 

 (probably species of Agrilus) (fig. 6); infection by bark fungi (including Cytospora 

 sp.); suppression; and occasionally, sunscald. Mortality caused by this mixed category 

 was especially prominent among the smaller trees. 



Figure 5. — Sooty bark canker, 

 caused by the fungus Cenangium 

 singulare in game-wounded por- 

 tion of the aspen trunk on the 

 left. The tree on the right 

 was also scarred by game, but 

 otherwise has remained healthy. 

 Note the advanced degree of 

 stand deterioration and the 

 absence of visible sprouts. 



7 



