FOREST PATHOLOGY IN FOREST REGULATION. 17 



susceptible to heart rot. No heart rot is possible before heartwood 

 is formed. Unfortunately, we do not know anything about the 

 formation of heartwood in our American species with relation to the 

 age of the tree. The younger trees, while at present immune, will, 

 in growing up and after formation of heartwood, become just as subject 

 to heart rot as are their older companions. It is, then, of prime 

 importance to know at what age living trees of a given species become 

 particularly liable to attack from the one or more heart wood-destroy- 

 ing fungi that use their heartwood as a source of food. It is, further, 

 of the utmost importance to know whether there are any conditions 

 in the tree or outside of it that exert an influence over the develop- 

 ment of the fungi once they have gained access to the heartwood 

 of a tree to which they are adapted. 



Beyond general statements to the effect that overmature trees do 

 deteriorate from heart rots, very little information is to be gathered 

 from American literature concerning the average age at which certain 

 tree species become liable to attack from heartwood-destroying fungi. 

 Greenamyre 1 mentions that in the Apache National Forest the 

 decay in Douglas fir " no doubt largely offsets the growth'' after the 

 age of 210 years is reached. 



Hunger 2 gives a little more specific information: 



The amount of decay found in living Douglas firs up to the time they are 150 years 

 old or so is very small, but in mature and overripe timber there is a great deal of 

 defect due to decay. . . . Douglas fir trees resist infection from fungi well until 

 they become mature, when, because of the opening up of a stand, breakage, and scars 

 due to the action of the elements and of fire and insects, and also because with advanc- 

 ing age their resistant power becomes less, they offer entrance to fungi. 



It is not clear from the context whether Hunger's figures are an 

 estimate or are based on actual methodic investigation and measure- 

 ments. 



Findley Burns, 3 in speaking of conditions on the Crater National 

 Forest, gives the following information : 



Many of the older Douglas firs are affected by a dry rot. . . . White fir is especially 

 susceptible to decay, and many trees above 40 inches in diameter on the forest are so 

 rotten as to be valueless, even for cordwood. 



In the latter case, age is supplanted by diameter, which answers 

 perfectly well if diameter invariably corresponds to age. 



Barrington Hoore and R. L. Rogers 4 incidentally give some 

 interesting notes on the age of infection of balsam fir, which on the 



1 Greenamyre, H. H. The composite type on the Apache National Forest. U. S. Dept. Agr., Forest 

 Serv. Bui. 125, 32 pp., 4 figs., 1913. (See p. 31.) 



2 Hunger, T. T. The growth and management of Douglas fir in the Pacific Northwest. U. S. Dept. Agr., 

 Forest Serv. Circ. 175, 27 pp., 4 figs., 1911. (See p. 10.) 



s Burns, Findley. The Crater National Forest. U. S. Dept. Agr., Forest Serv. Bui. 100, 20 pp., 4 pis., 

 1911. (Seep. 12.) 



4 Moore, Barrington, and Rogers, R. L. Notes on balsam fir. In Forestry Quart., v. 5, no. I, pp. 41-50, 

 1907. 



98035 Bull. 27516 2 



