- EEPRODUCTIOlSr OF WESTERN YEIJLOW PINE. 138 



MISCELLANEOUS ENEMIES. 



In addition, to damage by grazing, which is preventable, western 

 yellow pine reproduction suffers from a number of natural enemies 

 which are only in part or not at all subject to human control. Most 

 conspicuous among these enemies are fire, diseases, insects, and 

 rodents. 



FIRE. 



The destructive effects of fire are so obvious as scarcely to call for 

 discussion. Western yellow pine seedlings lack the fire-resisting 

 qualities which characterize the longleaf pine of the South. Seed- 

 lings below 2 feet high will scarcely resist an ordinary grass fire, and 

 where large amounts of inflammable material are present saplings and 

 even full-grown trees are subject to destruction or serious injury. 

 Although the Forest Service is developing an efficient system of fire 

 protection, occasional conflagrations covering 100 acres or even more 

 may be expected for many years to come. Since fires are most de- 

 structive and difficult to control where slash has been left after log- 

 ging, the desirability of burning the slash is obvious. Moreover, it 

 has been shown under " Brush disposal " that under most conditions 

 the burning of brush favors the establishment of seedlings by elimi- 

 nating excessive amounts of herbaceous vegetation. Grazing also 

 decreases the destructiveness of fire by preventing excessive accumu- 

 lations of grass and by breaking up and mixing pine needles and 

 other litter with the soil (9). The control of fires is a problem which 

 lies beyond the scope of this investigation. 



DISEASES. 



Western yellow pine seedlings in this region suffer relatively little 

 from fungous diseases. The damping-off disease attacks first-year 

 seedlings in shaded situations, but where they receive sufficient sun- 

 light comparatively little loss occurs in the forest. A disease an- 

 swering the description of " stem girdle," by Hartley (8) has been 

 observed. A more common disease is apparently what Hartley de- 

 scribes as " sun scorch." It occurs during dry periods of the grow- 

 ing season. This, however, is not a fungous disease, but is due to 

 excessive water loss and is therefore merely a manifestation of 

 drought. 



Long has called attention to a twig disease caused by a fungus, 

 probably Cenangium abietis, which in certain localities, notably the 

 Prescott National Forest, has injured western yellow pine saplings 

 to a considerable extent. 



