In view of current stocking levels, we consider the above condition as beneficial 

 to management of the areas for timber production. Trees in suppressed and intermediate 

 crown classes represent surplus stocking (table 1) . Their presence provides undesirable 

 competition for potential crop trees. The disease is effecting a natural thinning in 

 these crown classes. This will reduce competition and enhance growth and dominance of 

 potential crop trees. Unfortunately, the rate of natural thinning is inadequate for 

 optimal growth release. 



The disease situation in potential crop trees is very different from that recorded 

 for suppressed and intermediate crown classes. No mortality or severe top-killing was 

 recorded. Disease damage was much greater in shaded, lower portions of crowns than in 

 upper crowns. Although periodic terminal leader kill has reduced total height, it has 

 not caused any major stem deformity. Such damage can be detected only by closeup, 

 detailed examination of upper stems. Leader kill occurring more than 6 years ago is 

 no longer discernible. Normal growth form has not been altered. 



The greatest differences between the fertilized and nonfertilized areas were in 

 mortality and percentage of potential crop trees. The slight reduction in stocking 

 level of the fertilized area can be explained by a higher mortality level (table 1). 

 Our sampling was not adequate to estimate the total variation in disease severity within 

 and between the unthinned areas. We believe the higher percentage of potential crop 

 trees in the fertilized area is a direct result of the fertilizer treatment. The addi- 

 tional nutrients enhanced growth of the seedlings and permitted a greater number to 

 express dominance earlier. The high density of dominants and codominants created 

 environmental conditions, within these crown classes, more favorable for infection and 

 disease development. The result was a higher disease index for potential crop trees 

 in the fertilized area. 



CONCLUSIONS AND RECOMMENDATIONS 



We conclude that the current level of Sivococcus blight in potential crop trees in 

 southeast Alaska is no cause for alarm. This conclusion is based on our data and know- 

 ledge of the suscept and the disease. We believe the disease to be native to the area. 

 Infections were found in western hemlock more than 300 years old. The disease is not 

 restricted to young regeneration, but it is more noticeable in this material. -No 

 direct disease control measures are recommended at this time (Smith and others 1972) . 

 Monitoring of the disease in southeast Alaska should continue. 



Sivococous strobilinus is reducing height growth of western hemlock by killing the 

 terminal leaders. However, competition is the major cause of growth reduction in areas 

 surveyed at Thomas Bay. The regeneration is over 15 years old and dominance has been 

 expressed. We recommend that Timber Management personnel thin these stands to stocking 

 levels established for the Alaska Region. This will not only enhance growth of selected 

 crop trees, but will create environments less favorable for development of Siroooccus 

 shoot blight. The mixture of western hemlock and Sitka spruce should be maintained in 

 a reasonable facsimile of their natural ratio. 



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