408 JOURNAL OF FORESTRY 



mistakable evdence that they were then infested with Dendroctonus 

 species, so that it is logical to assume that the standing dead timber 

 on the area is a record of past losses from insect infestations 



The summary for the work on this project shows over 5,000,000 feet 

 of merchantable dead timber after applying a cull per cent of approxi- 

 mately 40 per cent for the whole project, or a gross volume of over 

 8,500,000 feet in trees which have been killed so recently as to be still 

 merchantable. In addition a total of 20,437 dead snags are reported 

 whose death must also be ascribed to the same agency. The average 

 volume for all live trees on the project was found to be 656 board 

 feet, and assuming the same average gross volume for the snags gives 

 a figure of 13,500,000 which, when added to the gross volume of 

 merchantable dead, gives a grand total of 22,000,000 as the evident 

 loss by insects in this block alone. It is difficult to estimate the number 

 of years' losses represented by this figure, but it is believed that 25 

 years is a conservative figure. Many trees killed will not stand this 

 long, but on the other hand, some will exceed this period, so that the 

 two should offset each other. Yellow pine of the size and quality 

 found on the project is usually about 300 years old. The loss from 

 insects during the life of the stand can therefore be obtained approxi- 

 mately by multiplying the loss attributed to 25 years by 12, which gives 

 264,000,000. The volume of standing green found on the area was 

 292,000,000 feet, and the difference 28,000,000, assuming that the 

 present stand represents the average growing stock that has existed 

 on the area, may be charged off as losses resulting from fungi weak- 

 ened trees blowing over, trees destroyed by the mechanical action of 

 lightning, etc. In other words, during the life of the stand 90 per cent 

 of the trees by volume will be killed by insects and 10 per cent by 

 other causes. 



It will be noted that the foregoing figures indicate an average annual 

 loss of about one-third of one per cent per annum over a long period- 

 of years, which is considerably less than the figures for annual loss 

 now occurring in some of our stands. This brings us to the discussion 

 of the variation in the annual losses. It is a well recognized fact that 

 insects have always been with us, and that losses rise and fall of their 

 own accord without control operations. It is, therefore, of great im- 

 portance to the forester to determine, if possible, if these variations 

 have a periodicity, as such a determination would greatly aid in estab- 

 lishing the proper time for the institution of control measures. I am 

 not referring to such widespread destruction as occurred in the Black 



