712 JOURNAL Of' FORESTRY 



The preceding paragraphs bring out the facts that the power of re- 

 sistance of unsound trees to heavy wind storms is very materially im- 

 paired, and by inference that sound trees possess a very much higher 

 resistance. These facts form a basis for general recommendations 

 regarding the sanitation of the forest as well as for windfall prevention. 



re:commendaTions 



Seed trees selected and marked to be left after the area is logged 

 should be sound and thrifty, not too tall nor with large, top-heavy 

 crowns. They should, if possible, be grouped for mutual protection 

 against the wind and should not be selected on exposed sites where the 

 wind action is strongest. For best results the soil should be compara- 

 tively firm and well drained, so as to safeguard against the loosening 

 of the soil by the melting of snows, heavy rains, and poor drainage. 

 Shallow soils with "hard-pan" layer just beneath should be avoided. 

 Shallow-rooted tree species especially susceptible to windthrow should 

 be reserved on wind-protected sites only. 



Similar recommendations are ofifered for application in marking 

 trees to be left upon an area following selection cuttings or thinnings. 



summary 



The conclusions derived from this study are as follows : Windfalls 

 are a financial loss in most cases, and where not harvested act as a fire 

 menace to the remaining stand or as developing centers for forest-tree 

 insects and forest-tree diseases. 



Windfall is prevalent in all types, sites, and localities which are most 

 favorable to windthrow. From the data secured and from observations 

 in the field, it appears that the lodgepole-pine type is the most suscepti- 

 ble to windthrow. Such sites as exposed ridges, gaps, and saddles in 

 ridges and sites unprotected from the full sweep of the wind are most 

 commonly given to windfall. From the viewpoint of locality, the data 

 recorded indicate the Pacific-slope region of the Northwest to be the 

 most severely damaged by the windfall, although the Rocky Mountain 

 windfall region forms a close second in respect to area covered. 



The force of the wind is classified as the primary cause of windfall, 

 and all other causes, such as cutting operations, fungi, soil, fire, snow, 

 height of trees, size of crowns, exposure, etc., are classed as secondary 

 causes. A certain amount of overthrow and breakage is traceable to 

 heavy snow and ice cappings as primary causes. 



Of the various secondary causes, those of cutting operations and soil 



