FUNGI AS CONTRIBUTORY CAUSES OF WINDFALL 697 



Fungi are the natural rot-producing agents in our forests, and attack 

 all species of trees, killing some outright, while in the majority of cases 

 decay renders the heartwood unmerchantable. Certain of these fungi 

 have been found operating almost exclusively in the roots and in the 

 butt portions of the tree. This has led to the question of the relation 

 fungi bear to the windfall problem and the extent to which fungi are 

 directly responsible for windthrow. It is a known fact that injuries 

 to standing trees, no matter how produced, form ready entrances for 

 rot-producing fungi. Dead branches of standing, living trees are often 

 broken off by wind. The resulting branch-stubs offer a ready means 

 of infection. FalHng trees often injure their neighbors, either by 

 breaking oft' branches or damaging the bark. These injuries favor the 

 entrance of fungi into the heartwood, and this is followed by decay and 

 subsequent loss. The relation of this phase of the windfall problem 

 to fungi is not very difficult to trace, but the part fungi play in causing 

 windfall is one which necessitates a more detailed and careful study. 

 The aim of this paper is to consider all the factors concerned in the 

 overthrow of trees by wind and to demonstrate the extent to which 

 fungi are responsible for windfall, as well as to consider other apparent 

 relations between fungi and windfall timber. 



CAUSES OF WINDFALL 



The primary or direct cause of windthrow is the force exerted by 

 air currents upon the crown surface exposed in the stand, the trunks 

 supplying the leverage. This force generally expresses itself in the 

 form of high-velocity winds and storms.^ Tornadoes, hurricanes, whirl- 

 winds, and other forms of air currents are found responsible in some 

 regions for the overthrow of great areas of timber. In some cases 

 windfall is produced by sudden and powerful draughts accompanying 

 large forest fires. These air currents sweep through narrow canyons 

 and over ridges, and by their force mow down large areas of partly 

 burned trees as well as portions of the stand untouched by the fire. In 

 the great fires of 1910, which swept away millions of acres of valuable 

 timber, the windfall due to the draught of the conflagration on the 

 St. Joe and Cabinet National Forests covered approximately 28,000 

 acres. GrouncJ fires of smaller importance often sweep through a 

 forest, severely burning the trees at the base and exposing and burning 



'Fiirst, H. : The Protection of Woodlands. 1893. Trans, by John Nisbet. 

 Classifies air currents as follows: Winds, velocity of 66 feet por second; storms. 

 66 to 116 feet per second; hurricanes, above 116 feet per second. 



