A NATIONAL PLAN FOE AMERICAN FORESTRY 701 



eradication of these diseases by a special control operation is rarely 

 warranted, since they do not threaten the perpetuation of any com- 

 mercial species. When timber is finally cut all diseased trees should 

 be removed, leaving only healthy individuals for seed trees or for the 

 nucleus of the next cut. This will reduce the amount of disease in 

 the reproduction, and where early thinnings are practicable, diseased 

 trees can be removed while they are still small, leaving the final crop 

 composed of healthy individuals. In certain managed hardwood 

 stands in southern Connecticut, where there is an active demand for 

 fuel wood, it is now the practice to thin out the undesirable trees early 

 in the life of the stand, with particular emphasis placed on the removal 

 of oaks suffering from Strumella canker. 



DISEASES AFFECTING MERCHANTABLE FORESTS 



Native killing diseases affecting merchantable forests do not usually 

 cause spectacular damage, but in the aggregate these losses are of 

 consequence, since almost every tree killed results in a corresponding 

 reduction in volume of the stand. Furthermore, killed trees usually 

 occur as scattered individuals or groups so that it is economically 

 impossible to salvage them. Parasitic fungi and mistletoes take a 

 steady annual toll from mature stands, and occasionally unfavorable 

 weather conditions cause heavy losses. Following a drouth period 

 culminating in 1925, mature trees died so extensively in the bottom- 

 land hardwood region of parts of the South, that the loss was believed 

 to equal a normal year's cut by the mills of the region. Occasionally 

 groups of mature trees are killed by lightning. While little can be 

 done to prevent killing of mature trees by adverse climatic conditions, 

 it will ultimately be possible to reduce losses caused by fungi and 

 dwarf mistletoes, through the elimination of infected trees when the 

 stand is cut so that the new, immature stand will not be exposed to 

 infection from old, diseased individuals. 



The great loss from fungus action in merchantable stands is in 

 the destruction of heartwopd of living trees by decay fungi. In 

 Douglas fir, the timber species on which the most extensive data are 

 available, this loss amounts to 17 percent. Since Douglas fir com- 

 prises nearly one third of the remaining saw timber of the entire 

 United States, the cull in this species alone means that more than 5 

 percent of our apparent timber supply is worthless. In other species 

 of which the remaining stand is much less, the percentage loss through 

 decay is even higher. In the mixed coniferous forests of northern 

 Idaho, western hemlock is so badly decayed as to be largely unmer- 

 chantable. Throughout much of the range of white fir, cull from 

 decay is so heavy as to amount to complete destruction of the mer- 

 chantable stand. In the Adirondack Region of New York, loss from 

 decay in beech is so high as to make this species of doubtful value. 

 The same species is so defective in the bottomland hardwoods of 

 Louisiana that it is frequent practice in logging operations to leave all 

 of the beech trees standing. It is figured in the northern Rocky 

 Mountain region that defect, largely decay, increases the unit cost of 

 timber production in nearly the same ratio as the occurrence of the 

 defect itself. In addition a much larger ratio of low-grade lumber is 

 produced from a defective stand than from a sound one of similar 

 growth rate. These lower grades are difficult to sell even during a high 



