288 JOURNAL OF FORESTRY 



greater portion of this region. Another cause of loss in heavy soils is 

 ground heaval, due to alternate freezing and thawing of the upper 

 soil strata. Plants whose roots do not extend below the strata affected 

 by this action are often thrown completely out of the ground. Severe 

 frosts early in the fall, before the seedlings have time to harden, may 

 result in wholesale losses, although this has occurred only once during 

 the 9 years in which the writer has been in this region. 



Aiter the period of infancy the seedlings are still endangered by a 

 long list of enemies. Most prominent among these are fire, snow pres- 

 sure, grazing, and insects. 



Fire usually kills all seedlings which happen in its path. Fortunately 

 ground fires, unless there is a large amount of grass or slash, seldom 

 make a clean sweep. The survival of occasional patches of reproduc- 

 tion on burned areas is due to this circumstance. The extent to which 

 the failure of reproduction in the past has been due to fire is difficult 

 to determine. Severe fires, such as occur in slash after cutting, leave 

 a distinct imprint in the form of fire scars on living trees, and thus the 

 year of occurrence can be determined. Light fires, which merely kill 

 seedlings but do not injure trees, are more apt to escape notice. There 

 is little doubt that in most cases where virgin forests lack reproduction 

 in the openings, where it could grow without coming into destructive 

 competition with older trees, fire is the controlling factor. With our 

 fire-protection system continually reaching a higher state of perfection, 

 this source of damage will be greatly reduced in the future. It should 

 be borne in mind, however, that a fire once in 20 years may keep out 

 reproduction. 



It has recently been discovered that snow does more damage to seed- 

 lings than was formerly appreciated. In the spring of 1916 a plot of 

 broadcast sowing containing a dense stand of 2-year-old seedlings 

 showed severe damage. The seedlings were broken at the ground line 

 by the weight of the snow. On a number of sample plots south of 

 Flagstaff seedlings 5 to 10 years old are commonly bent and otherwise 

 deformed without showing signs of insect or grazing damage. The 

 evidence points to snow as being the cause. 



No diseases have been reported as doing serious damage to seedlings 

 in this region. Possibly this is because too little is known about dis- 

 eases by forest officers. Mistletoe attacks saplings, but rarely appears 

 on seedling growth below 3 feet high. 



Grazing, particularly by sheep, is responsible for much damage in 

 certain localities. The severest damage is on the Coconino and 



