FUNGI AS CONTRIBUTORY CAUSES OF WINDFALI, 701 



system of spruce has been reported by Matthes." He finds that spruce 

 trees are rendered more windfirm on areas where species of lupine and 

 alder are growing in close proximity to them. It is stated that the 

 spruce on such areas possess greatly extended and penetrating root 

 systems, and these are due to the presence of nitrogen-producing bac- 

 teria in the root nodules of lupine and alder. The spruce roots have 

 been found to grow toward these nitrogen-supplying nodules, thus 

 stimulating the roots to further penetration into the soil. 



Aside from the roots the shape and height of the tree bear important 

 relations to the action of the wind. Dense stands produce tall, top- 

 heavy trees, whose size and position of crown place them in a favorable 

 position for windfall. This has been found true of several species of 

 trees, but more particularly so for the lodgepole pine.^^ Pure stands 

 and the age of stands also are factors in wind resistance. Pure stands 

 of shallow-rooted trees are less windfirm than if occurring in a mixture 

 with other more deep-rooted species. Pure stands, with the exception 

 of a few species, are also inclined to become dense. 



The danger from windfall increases directly in proportion to the age 

 of the stand. With age come larger and taller trees, larger and denser 

 crowns, and greater mass. These all contribute to the greater leverage 

 and windfall damage is thereby increased. Hess," Nisbet,^®, Sterrett,'" 

 Baker,^ Smith and Weitknecht,^* and Mason^^ state that the increasing 

 age of the stand also increases the danger from windfall. The obser- 

 vations of Smith and Weitknecht^® show that the largest, tallest, and 

 heaviest-crowned trees were the most subject to windfall. Baker^ came 

 to a similar conclusion in his observations upon a windfall area of 3,480 

 acres in the Olympia National Forest in Oregon. 



The factor of increasing age brings up the point which is the para- 

 mount consideration in this paper. Previous works^'- ^^ have shown 

 that with increasing age in fungous-infected trees comes a proportion- 

 ate increase in the volume of rot. This holds true for a tree species 

 after it has entered the infection age which determines the earliest age 

 at which the fungus enters. Since the roots of trees are particularly 

 designed as braces and anchors for the resistance of windthrow, and 

 since root and butt rots are common in most species of trees, it is 

 readily seen that the action of fungi must bear some important relation 

 to the relative wind resistance of infected and uninfected trees. In- 

 creased decay, whether of the trunk or of the roots, represents a pro- 

 portionate decrease in the strength of those parts and a reduced resist- 

 ance to the force of the wind. Therefore, most of the other factors 

 remaining constant, it is believed tliat a tree having sound roots resists 



