A STUDY OF HEAET-EOT IN WESTERN HEMLOCK. 37 



The fungus enters mainly through branch stubs. Frost cracks 

 play a minor part as first-infection injuries. From the point of first 

 infection, apparently coincident with the largest sporophore, the. 

 decay extends up and down the heartwood until all the susceptible 

 heartwood is attacked. The extent of decay is found to increase 

 with age. A high degree of injury, large numbers of sporophores, 

 low vigor, and smaller crown sizes appear to develop more or less 

 parallel with the increase in decay. 



The environmental factors in the river-bottom type are more 

 favorable to the early and extensive development of decay. A large 

 percentage (97) of the total trees of the northern Idaho plats examined 

 were found to be infected. Of 10 trees less than 60 years old and 

 3.5 inches in diameter breast high, 9 were infected. 



The environmental factors in the southwestern-slope type are less 

 conducive to early decay. The maximum development of the fungus 

 is not reached until the stand is old. 



A large nimiber of sporophores are produced on both sites, the 

 river-bottom site on a comparison basis of age class showing the 

 greater number. The 48 trees over 160 years of age bore an average 

 of 3.7 sporophores per tree. 



Pathological cutting ages based upon data secured by thorough 

 pathological surveys and adjusted to the economic factors concerned, 

 if applied to all stands of hemlock, would aid greatly in checking the 

 spread of the disease and would determine the cutting age of the 

 stand before the increase in rot became too great for economic 

 logging. In the present study this could be applied to the slope 

 type only, since the trees of the river-bottom type are all below 

 merchantable size. 



A rigid sanitation clause inserted in all timber-sale contracts 

 involving western hemlock should be aimed principally at the destruc- 

 tion by fire of all infectious cull material as well as all infected trees 

 left standing. Girdling by the ax is not recommended. 



These two control methods, when adapted to the situations they 

 best serve, will pave the way to the sanitation of the western hemlock 

 stands as well as other types of forests in the Northwest. 



