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A STUDY OF HEART-ROT IN WESTERN HEMLOCK. ou 
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 number 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 hemiock should be aimed principally at the destruc- 
tion by fire of all infectious cull material as well as all infected trees 
left standing. Guirdling 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. 
