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forest enemies left another chance, and they begin to increasei Then We 

 havo another period of heavy danage in the forest* 



Such outbreaks have probably been happening from tiaie to time since 

 thejB were any woods. VJe have the record of baric-beetle outbreak, engraved 

 inside a ^ismt tree; and accurately dated, by the tree-rings, as having 

 taken place four hundred years ago. 



Nor is all the evidence of past outbreaks confined to such insects as 

 baric-beetles which directly damage the stem of the tree by boring in,to it. 

 Evon the insects which feed on the leaves, Dr. Craighead says,' leaVe a, 

 permanent record in the tree-rings of the trunk. Severe destructio^n of the 

 top by certain insects causes a marked reduction in the width of the ann^ual 

 layers of growth put on by the tree. Dr. Craighead says that the l^ater rings 

 through the entire stem are narrower for several years. Then, if t^he tree 

 recovers, normal growth rings begin to be formed. So typical are the 

 patterns formed by the tree rings that they can be definitely distih^fuished 

 from all other known causes of retardation of growth. For instance, a 200 

 year old spruce examined by Dr. Craighead sliowed there had been an outbreak 

 of spr-dce bud worms beginning in 1807 and another unusually severe outbreak 

 of that insect in 1913. 



Such records prove that insect danage goes on even in the wild, un- 

 touched, virgin forest. In many cases, since man has gone into the forest 

 to cut wood he has upset the natural scheme of things in such a way as "bo 

 help the forests' insect enemies. 



For example, the original forests of our IJorthwest were a mixture of 

 white pine, spruce, and fir. Along came the lumberman interested at first 

 in white pine. A little later, he took the finer spruce. All the gaps made b; 

 taking out the white pine and spruce were filled up by fir. That made things 

 better for the spruce bud worm. The spruce bud wonn can only becaae abundant 

 when there is plenty of fir for it to breed on. When the fir came in where 

 the white pine and spruce had been cut out, the bud worm which destroys 

 both spruce and fir, multiplied fa$t and spread easily. Twenty-five years' 

 pulpwooQ supr)ly was destroyed in that region one year. 



Another illustration of how man has helped insects destroy woods is 

 the cause of the turpentine borer and the turpentine industry of the South, 

 The t-orpentine borer tunnels into the turpentine pines and weakens the wood, 

 so that the stems break over in the wind. But the turpentine borer has to 

 have an opening into the tree. It will not attack through the bark. In 

 fact. Dr. Craighead sa^'s that the turpentine borer used to be classed as a 

 rare species of insects. 



Then came man in his greed to get the biggest return in the shortest 

 possible time. In the Gulf States, South Carolina, ajid Georgia, a very de- 

 structive system of blazing or chipping; the pines to get turpentine was 

 practiced. That is, it became customary to cut such wide faces, that the 

 scars left didn't heal over promptly. That was an opportunity for that 

 rare insect. The borers could get in. Pretty soon the turpentine borer 



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