698 JOURNAL OF FORESTRY 



the roots. This greatly weakens the tree, and the first wind of suffi- 

 cient force causes a windthrow of the weakest ones. 



Other but less frequent causes of windfall and windbreakage are 

 found in unusually heavy snowfalls, heavy sleet and ice cappings, and 

 in extreme low temperatures accompanied by wind. Occasionally 

 heavy snows or ice cappings are to be classed as primary causes, since 

 they cause overthrow, bending and breaking of trees without the aid 

 of the wind. The increased weight upon a tree of a large mass of 

 snow or ice or sleet causes the tops of the weaker trees to bend over 

 and sometimes to break. Many are broken o& near the tops or lower 

 down on the trunk, while others are bent over low on the ground or 

 overthrown. In the winter of 191 5 a very heavy snowfall, accom- 

 panied by sleet, occurred in all the forest regions of Montana and 

 northern Idaho. A large amount of damage was done to young trees 

 in unprotected situations, to mature tall trees in dense stands, and to 

 weak trees by breakage of trunk and branches and by bending to such 

 an extent that recovery to a normal position was impossible. During 

 the same winter, on the Missoula National Forest near Bonner, Mon- 

 tana, a severe early cold spell, accompanied by high winds, caused a 

 phenomenal loss of the outermost tips of the branches. After the 

 storm the ground was carpeted with green branch tips from 2 to 10 

 inches in length of various conifers. The extreme low temperature 

 made the branch tips very brittle, and the high wind succeeded in break- 

 ing them off in large quantities. This is a considerable loss, viewed 

 from the angle of seed and needle production, since a great number of 

 the pollen and seed cones as well as leaf buds were removed with the 

 twigs. The Douglas fir (Pseudotsuga taxifolia (Lam.) Britt.) suf- 

 fered the greatest loss. Mason^-*^ gives an account of snow damage to 

 lodgepole pine {Pinus contorta Loud.), which usually occurs on young 

 trees 4 inches or less in diameter, bending them to the ground or break- 

 ing them off at a height of from 10 to 20 feet. 



The secondary or indirect causes which are concerned with windfall 

 of trees are more numerous and complex, ranging from the activities 

 of forest management to the effect produced by root- and butt-rotting 

 fungi. So many of these factors are found combined as secondary 

 causes that it is difficult to single out any one cause as predominant in 

 its effect. Usually two or more causes will be found of nearly equal 

 importance in relation to the wind damage to particular trees. Briefly, 

 the various factors will be taken up, commencing with such causes 

 produced by the activities of forest management. 



