BASIC PROBLEMS IN FOREST PATHOLOGY 219 



the most highly prized broadleaf species of the East and is heavily 

 represented in the States east of the Mississippi. The values involved 

 reach many millions of dollars. In its native habitat, China, the same 

 disease does scant damage to Chinese chestnut trees which are of 

 little value. Of low virulence, on Chinese chestnut, it is exceedingly 

 aggressive in the eastern chestnut forests. The relative importance of 

 the disease with regard to economic values threatened, to representa- 

 tion of species and to aggressiveness, must, therefore, be given a very 

 high rating in the United States, but a very low one in China. On 

 the other hand, the trees are killed but not destroyed by the disease. 

 The character of the damage cannot be considered to be nearly as 

 serious as that done by wood-destroying fungi, since evidently' the 

 economic values oi a tree are not represented by its living organs but 

 by the lumber it contains. The menace to the lumber contained in 

 trees killed by the chestnut-bark disease does not come from Endothia 

 parasitica, the cause of the disease, but from secondary, wood-destroy- 

 ing fungi and insects. The killed trees can be utilized if cut in time. 

 It is only when the killing takes on such proportions as to make 

 immediate utilization impossible that the ultimate efifect is the same as 

 though the timber were lost through heartwood-destroying fungi. In 

 a general rating as to the relative importance of the chestnut-bark 

 disease this point must be taken into account. 



Another example: Polyporus sulphureus in the Sierra Nevada 

 causes a very common and destructive heartrot of red fir (Abies 

 magnifica). It generally appears in the butt of the older trees, which 

 finally break off in heavy storms. But Abies magnifica grows only 

 at high elevations from about 6,000 to 8,000 feet, forming large stands, 

 of which but few are accessible. At lower elevations the fungus seems 

 to be confined to oaks of very little value. The relative lumber value 

 of Abies magnifica is not high; it ranks somewhat better than Abies 

 concolor. The relative importance of Polyporus sulphureus in stands 

 of Abies magnifica must be given a low rating in spite of the fact that 

 it does destroy very large quantities of lumber. In the same stands 

 Polyporus sulphureus occasionally appears on Pinus lambertiaua, the 

 most valuable of the pines of the Pacific Coast. But this pine is dis- 

 tinctly outside of its range in the red-fir belt. It is weakly represented 

 and the disease seems to be so rare on this species that in spite of the 

 intrinsic value of Pinus lambertiaua but a low rating can be given to 

 Polyporus sulphureus in this case. 



