730 A NATIONAL PLAN FOR AMERICAN FORESTRY 



injured. Recent investigations of this problem, although not yet 

 completed, indicate that the vigor of the individual tree is the most 

 important factor in regulating locust borer damage. Damage occurs 

 in inverse relation to vigor that is, the more vigorous the tree the 

 jess the damage and, furthermore, the borer itself cannot develop 

 in vigorous trees. At present the application of these findings indi- 

 cates that the solution lies in management through coppice and 

 development of more vigorous strains for planting on waste lands. 



For a number of years prior to the conclusion of recent studies 

 the bronze birch borer was by some foresters regarded as a serious 

 forest problem in the management of mixed hardwood stands in 

 northern New England and the Lake States. It is of practically no 

 importance in an uncut forest, except in one which is overmature 

 and where general decadence has set in, but appears in great num- 

 bers coincident with the death of the trees left after partial cutting 

 of the original stand. It has been shown that the changes in the 

 physical factors of the environment brought about through the me- 

 dium of logging are often such that trees left will succumb without 

 the attack of either insects or fungi, and the borer plays only the 

 role of a secondary factor in hastening post-logging decadence. 



The application of these studies has indicated that selective logging 

 in any forest which contains a large percentage of birch is a danger- 

 pus practice where more than 25 percent of the basal area of a stand 

 is removed. Where cutting is heavier than this, factors of decadence, 

 of which the bronze birch borer constitutes only a minor one, are 

 such that losses will more than offset growth in the period following 

 cutting. 



Much progress has been made in recent years toward establishing 

 sustained yield on both Federal and private timberlands in the 

 ponderosa-pine type of California and Oregon. The management of 

 these stands is based on an initial partial cutting, leaving a sufficient 

 reserve of timber for future growth so as to enable a second cutting 

 in from 30 to 40 years. Bark-beetle losses in these stands reserved 

 for future growth have in certain areas not only offset all increment, 

 but have reduced the original forest capital from 1 to 15 percent. 

 Recent experiments have indicated the possibility of avoiding this 

 loss by removing insect-susceptible trees in the initial cutting. These 

 susceptible trees are those of slower growths which can be detected 

 at the time of marking the timber for sale. Recent sales have been 

 marked on this plan. 



FOREST INSECTS AND FOREST PRODUCTS 



Federal research into the damage and methods of prevention of 

 insect losses to crude and finished products has resulted in great 

 savings to the industry. Losses in this character of material can 

 frequently be prevented by very simple means, such as prompt move- 

 ment of the felled logs from the woods so as to avoid exposure during 

 the period of insect activity, storing the freshly felled logs in water, or 

 exposing them to direct sunlight during the summer months. At the 

 mill of storehouse prevention can be accomplished by proper inspec- 

 tion, by segregation and classification of the stock of material on hand 

 so as to insure that such material as the sapwood of a hickory, walnut, 

 or oak is not held under conditions subject to attack by powder-post 



