A NATIONAL PLAN FOR AMERICAN FORESTRY 713 



rust control are considered. A dying out of the species is to be ex- 

 pected in the marginal portions of the range, where its representation 

 in the stand is not heavy enough to justify control measures. On the 

 other hand, in some of the outlying sections where the alternate hosts 

 can be cheaply eradicated and growth rate and markets are favorable 

 to the pine, it is probable that white pine production in the future 

 will be greatly increased through planting. In the major portions 

 of the range in which protection is practicable, the cost per acre of 

 the protection ranges from 5 cents to $2 per acre, with an average 

 of 44 cents. This figure covers all charges Government, State, and 

 local, as well as the actual cost of removing the bushes. In most 

 places eradication of alternate hosts is advisable at about 5-year 

 intervals, but the cost of these later eradications is less than that of 

 the initial one. 



The status of the blister rust in the West is less hopeful. Western 

 white pine and sugar pine are still more susceptible than the northern 

 white pine, and the currants and gooseberries that act as alternate 

 hosts in the West are more numerous, more congenial to the rust, 

 and more difficult to eradicate. Both the infection and the control 

 campaign in the West are relatively recent, and the proportion of the 

 stand of these two important western timber species which can be 

 protected from rust at a practicable cost in the present profitless 

 state of the local lumber industry remains to be determined. It is 

 feared that most of the privately owned white pine stands of Idaho 

 will be destroyed because of the inability of the owners to finance 

 control. 



Both the chestnut blight and the blister rust, where allowed to run 

 unchecked, affect the aesthetic and thus the recreational value of the 

 forest to an extent not encountered with most native diseases. So 

 many trees are killed at once that it takes many years to replace the 

 skeletons of the killed trees with enough trees of other species to 

 restore the beauty of the forest. To a great many people the species 

 which replace them are decidedly inferior in beauty to the chestnut 

 with its remarkable spreading branches or to the white pine with its 

 dark masses of foliage. 



In the case of chestnut blight, the wholesale killing of the trees 

 on thin soils on upper slopes in places in Pennsylvania has in some 

 cases resulted in soil deterioration through opening up of the stand 

 to such an extent that the humus layer has disappeared and centuries 

 may be required to restore the original value of the watershed. 



Even where a lost timber species is replaced promptly and com- 

 pletely by others of equal commercial and aesthetic value, there is 

 chance for indirect and deferred damage to the forest. Most of our 

 forests are balanced associations of a number of species of trees and 

 shrubs, and the soil organic matter is largely controlled by the species 

 mixture. There are numerous ways in which these species can affect 

 each other, and the complete removal of any of the commoner species 

 may result in soil changes unfavorable for the entire association, or in 

 otherwise so unbalancing the forest-tree community as to seriously 

 reduce its productiveness. 



The other introduced diseases of our time appear thus far to be less 

 serious because they are less active, because they are attacking trees 

 of less economic importance, or because they have been introduced in 

 localities where the most susceptible native tree species are not com- 



