INSECT LOSSES TO SUSTAINED YIELD 411 



In our overmature stands we find the proportion of thrifty "black- 

 jacks" attacked and killed just as high as the proportion of veterans 

 that are attacked and killed. In fact, just as often as not the swarming 

 broods will pass up old scraggy veterans to attack "blackjacks" and 

 poles. In numerous instances the insects will be found working year 

 after year in patches of pole timber, killing out a few trees each year, 

 and making no effort to leave the pole patch to attack decadent trees 

 within a limited distance, until the stand of poles has been almost 

 entirely eliminated. 



Marking in our stands of western yellow pine is governed first by 

 the necessity of leaving sufficient trees for seed and secondly the leaving 

 of as many thrifty trees as possible to form the nucleus of a second cut. 

 As has been previously pointed out the beetles of Dendroctonus species 

 are apt to pick out the most thrifty individuals and it is easily conceiv- 

 able that the killing of a small part of the reserved stand may remove 

 the possibility of natural reseeding over small areas within the stand, 

 either lengthening the period of regeneration, or reducing the degree 

 of stocking for the whole unit. The first, of course, lengthens the 

 rotation, and the second reduces the real growing stock and the final 

 return. I do not wish to convey the impression that to the losses of 

 seed trees through insect attack is due the lack of reproduction in 

 western yellow pine, but it must be perfectly clear that the subsequent 

 loss of trees which were left for seed purposes has a direct adverse 

 bearing on possible reproduction. In view of the difficulty of securing 

 reproduction in stands of this species, no reasonable effort should be 

 spared to give the cut-over areas as favorable an opportunity for re- 

 stocking as possible. 



The eflFect of varying and unexpected losses in the growing stock 

 needs but little discussion. Under any system of management, certain 

 departures from the working plan will be necessary on account of 

 unforseen contingencies, but in the degree to which these can be elimi- 

 nated, by that much is the administration of the plan simplified. The 

 death (and under a system of management we may assume the cutting) 

 of trees which become infested cannot be considered as an intermediate 

 return but as subtraction from the final return, and results in a decrease 

 of the real growing stock and the mean annual increment. Further, the 

 appearance of an epidemic infestation may require an entirely new 

 allocation of the cutting series or area, and defeat the objects of 

 management through the cutting of the timber into products which the 

 plan of management does not contemplate. 



We should, therefore, make every possible effort to eliminate as 

 fully as possible all infestation from our present stands, especially when 

 these are cut over, since the presence of insect infestation in the new 

 growth not only will represent a serious economic loss and expense for 

 protection, but will also present an unwarranted interference with 

 the plans for a sustained yield. 



