720 A NATIONAL PLAN FOR AMERICAN FORESTRY 



become heavy. Consequently losses in present young stands are 

 largely avoided if they are cut before they attain the age at which 

 decay becomes economically serious. In addition, determination of 

 outward indications of decay in living trees have enabled volume 

 estimates of standing timber of certain species to be made more 

 exactly, thus reducing one element of uncertainty in the lumber 

 industry, since the investment in all logging operations is based on 

 the amount of available timber determined by ocular estimates. 

 Some operators on private land in the Douglas fir region of western 

 Oregon and Washington have also used this information to leave 

 unmerchantable decayed Douglas fir trees standing and thus save 

 felling costs. There this practice will not cause increased decay in 

 the future, because the new Douglas fir forests will be cut before reach- 

 ing the age at which significant loss from decay begins. However, 

 under usual conditions decayed trees should be cut along with the 

 others to protect future stands. So far only a few important species 

 have been studied and many more remain for future work. 



When practicable, direct control measures must be applied to 

 virulent, introduced killing diseases, since it is these diseases that 

 may eliminate a native species as a factor in commercial timber 

 production. The commercial extinction of chestnut, now in progress 

 of accomplishment by the Asiatic blight fungus, cannot be stopped 

 by any economically feasible measure ; it had become too thoroughly 

 established for successful eradication long before the systematic 

 study of forest pathology was begun in the United States. The 

 equally dangerous white-pine blister rust which reached this country 

 some years later has been more successfully met. Investigation has 

 shown that the fungus causing the disease must have two kinds of 

 hosts for its existence the pines, and currant or gooseberry bushes. 

 While the disease can spread over 100 miles from pines to the alter- 

 nate hosts, its effective spread from currants and gooseberries back 

 to pines is only a few hundred yards ; so that effective control is now 

 obtained by eradicating currants and gooseberries in and around 

 valuable pine stands. This control is being extensively applied on 

 Federal, State, and private forest land in the East where about 9 

 million acres have been initially cleared of currants and goose- 

 berries, and a beginning is being made in the West; but because of 

 the greater difficulty and consequent increased cost of eradicating 

 wild-currant and gooseberry bushes there and the rapidity with 

 which the disease is spreading, the extent of stands of sugar pine 

 and western white pine that it will be feasible to protect is still 

 problematical. 



Valuable protection against the introduction of diseases from 

 foreign countries is given by quarantine. All forest trees and nursery 

 plants are now excluded from the United States except for importa- 

 tion under special permit with provision for periodic inspection for 

 the first few years after introduction. If a dangerous disease is known 

 to exist on a foreign tree, it cannot be imported at all except in limited 

 numbers by the Department of Agriculture and must then be held 

 in a Federal quarantine house a sufficient time for any disease to 

 develop. There is no restriction on the importation of seed, unless 

 it is known to carry a specific disease, and no safeguards are con- 

 sidered practicable on the entrance of wood, either in the form of 

 Jogs or in the less dangerous forms of packing cases, paper pulp, etc.. 



