EEPRODUCTION OF WESTERN YELLOW PINE. 135 



destroying insects undoubtedly far more than offsets any damage 

 which may be charged against them. 



Squirrels, rabbits, rats, gophers, and porcupines are responsible 

 for much damage by gnawing the bark. Squirrels confine their 

 activities mainly to cutting terminal twigs from the older trees. 

 Often the ground underneath a tree is completely covered with leaf 

 tufts cut off by squirrels. The obvious effect is to lower the capacity 

 of the crown as a food laboratory. Rabbits work on seedlings and 

 saplings, from which they gnaw the bark, or, in the case of seedlings, 

 sometimes cut off the entire plant. It is probable that squirrels, 

 rats, and gophers share in the blame for these depredations. Por- 

 cupines kill or seriously injure great numbers of seedlings from 1 to 

 6 feet high by partial or complete girdling. The writer has in mind 

 one area of 125 acres bearing an average stand of 80 seedlings per 

 acre between 1 and 3 feet in height on which scarcely half the plants 

 have escaped injury. In another instance a 5-year-old yellow pine 

 plantation covering one-fifth acre was almost completely extermi- 

 nated by girdling. It is not positively known, however, whether 

 this was done by porcupines or gophers. Strange to say, adjacent 

 plots of Douglas fir were untouched. Death does not ensue unless 

 girdling is complete, and even in this case seedlings have been known 

 to recover by developing a leader from one of the branches below 

 the girdle. Often the girdled stem becomes so brittle as a result of 

 excessive pitch exudation that it breaks under a load of snow. In 

 winter porcupines work mainly on trees beyond the sapling stage. 

 They bark the stem near the top over a space of several feet. As 

 in the case of younger trees, the wood becomes brittle and the top 

 often breaks off after a heavy snowfall. 



SUMMARY. 



It has not been possible in this investigation to cover in detail 

 all the conditions occurring in the j^ellow pine type of the South- 

 west. It is believed, however, that in solving the reproduction 

 problem where conditions are at their worst, namely, on the Coco- 

 nino and Tusayan National Forests, principles have been established 

 which will render it comparatively easy to meet the special cases 

 which may arise in other localities.-^ 



^ As this manuscript was being completed, there appeared in the October, 1921, issue 

 of the Journal of Forestry an article entitled, " Yellow Pine Reproduction," by Walter J. 

 Perry. Perry's article is based entirely upon observations on the Carson National 

 Forest in northern New Mexico. . Reproduction is generally excellent in that region and 

 the seedlings are considerably older than those which formed the basis for most of 

 the studies on the Coconino and Tusayan. Notwithstanding the differences in location, 

 soil, climate, and age of reproduction, the two investigations, which were independent of 

 each other, reach identical conclusions on practically all points covered by both. 



