2 BULLETIIS" 1m, U. S. DJgPAPiTPMEJSTT OF AGKICULTURE. 



relation of various factors to the rots, and the means by which the 

 loss may be reduced. This, in short, states the purpose of this 

 bulletin. 



LOCAL PATHOLOGY OF WESTERN WHITE PINE. 



With the exception of the principal fungus {E chinodontiwiv tine- 

 toriwrn) attacking western hemlock and grand fir, all fungi occur- 

 ring on other trees of the western white-pine type attack white pine 

 to a greater or lesser degree. Until it is determined that the inter- 

 relations of these fungi vary with different species of trees the con- 

 ditions for fungous development may be considered very favorable. 

 The western white-pine type of forest is described as having western 

 white pine as the key tree and forming approximately 15 per cent 

 or more of the stand. In some parts of its range (northern Idaho) in 

 young stands western white pine forms as much as 50 per cent or 

 more of the-stand. The other species in the mixture are grand fir 

 and western red cedar, the predominant trees of the type, and Doug- 

 las fir, western larch, western yellow^ pine, and lodgepole pine. In 

 many of the mixtures of the western white-pine type, the white pine, 

 although intermediate as to tolerance, very rapidly gains on its asso- 

 ciates and eventually overtops them or may even drive them from 

 the stand. One of the results of this suppression of associate species 

 is to promote the activities of fungi in the associate species, which 

 in turn react on the white pine. Fully stocked or even pure stands 

 of western white pine may be found extensively attacked. In the 

 fully stocked stands the trees do not prune readily, causing the de- 

 velopment of larger and older dead branches which are open to 

 breakage and infection at an earlier age and also affecting the grade 

 of lumber of the tree. In the pure stands, much suppression naturally 

 results and fungous diseases are just as prevalent as in a mixed stand. 

 Suppression in white pine is not always brought about by overcrowd- 

 ing or by adverse conditions on sites having little protection. l!^eedle 

 fungi may cause retardation by destroying the needles. Lophoder- 

 miujn pmastri, in its ascigerous stage and also in its pj^cnidial stage 

 (Leptostroma) , is a very common needle fungus throughout the 

 white-pine type and is a factor to be considered in suppression. 

 Mistletoes rarely attack white pine within its merchantable range 

 and may be overlooked as a cause of suppression. 



The three main wood-destroying fungi ^ for the areas studied are 

 Trametes pini, Polyporus schweinitsii, and Fomes annosus. The first- 

 named fungus, as the most important, is particularly active in w^est- 

 ern white pine throughout its merchantable range. 



1 Weir, J. R., and Hubert, E'. B. Forest disease surveys. U. S. Dept. Agr. Ful. 658, 

 23 p., illus. 1018. 



