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AMERICAN FORESTRY 



mature and later turn into moths which in turn lay large 

 numbers of eggs. Thus it is that an epidemic starts. 



The moths in flying over the forest seek out and alight 

 on the tops of fir trees. The first year feeding is almost 

 exclusively on fir, spruce being almost free from injury. 

 The second season again finds the moths in flight, 

 some of which, however, remain and lay their eggs on 

 the spruce. This accounts for the fact that the greatest 

 injury is to the fir. Counts made on hundreds of thou- 

 sands of trees show that the relation between dead spruce 

 and dead fir is seldom greater than two to three. This 

 emphasizes the fact that the intensity of an outbreak 

 depends largely upon the amount of fir that is present in 



AREA OVER WHICH INSECT HAS SWEPT 



Spruce flat showing some typical budwortn killed trees. The 

 hairy moss which clings to the branches often gives the appear- 

 ance of foliage in photographs. 



a stand. This habit of the moths seeking fir that is 

 growing in the sunlight accounts for the fact that spruce 

 and fir found in mixture with hardwoods is fairly im- 

 mune from budworm attack. It also accounts for the 

 fact that spruce and fir coming up under the protection 

 of hardwoods or budworm killed timber, is seldom dam- 

 aged. 



Many reasons have been given, all in good faith, for 

 the periodic appearance of the budworm, but few of 

 these take into account the fact that during an active 

 outbreak the caterpillars are present in such swarms and 

 over such a great territory that it is utterly inconceivable 

 that either birds or parasites could check their advance. 

 The one great factor is lack of suitable food. When the 

 fir is gone the outbreak soon dwindles down to nothing. 

 I do not want to detract from the great good that para- 

 sites and birds do in holding insects in check, but there 



comes a time when even these agencies are like a reed 

 before a hurricane. 



This brings us to the aftermath of a budworm out- 

 break. Conifers, unlike hardwoods, have very little re- 

 serve food, so that a single defoliation is a very serious 

 matter and so weakens the tree that it is easily subject 

 to attack by bark-beetles, other insects, and fungi. The 

 yearly dying of trees following an outbreak has been 

 found by the Canadian authorities to be comparable "to 

 a greatly accelerated natural thinning that takes place 

 in the normal forest." In other words, it is the sup- 

 pressed, over-mature or weakened trees that go first. 

 The greatest loss to the forest comes not from the defo- 

 liation by the budworm itself, but from these secondary 

 enemies which swarm into areas where there are large 

 numbers of weakened trees. Most of the field reports 

 mention these bark-beetles and borers as being present 

 in large numbers in the remaining timber. Trees de- 

 foliated and thus weakened by the budworm are also 

 made very subject to winter killing and fungi. In sample 

 plots taken in Canada over 75% of the dying fir was 



SALVAGING THE DEAD AND DYING TIMBER 



The increased demand for pulpwood during the war caused 

 much of the then dead timber to be salvaged. This problem of 

 salvaging dead timber is still a big factor in Maine. 



found to be affected by a root fungus which itself easily 

 kills weak trees. 



An insect outbreak is very much like a fire in that if 

 found in its early stages it is easily stamped out, but if 

 allowed to run and assume great proportions the chances 

 of stopping it under present forest conditions, are very 

 slight. The control of the budworm must take the form 

 of prevention rather than control. Knowing the habits 

 and life history of the insect which are so set that strong 

 interference at any point will upset their development it 



