28 ABSAKOKA DIVISION OF YELLOWSTONE FOKEST BESEBVE. 



mixed composition prove that occasionally the fires did not consume or kill the entire 

 stand. But as a rule most of the older fires made a clean sweep, and in nearly every 

 instance the fires of modern date have dbne the same. 



The destructiveness of the fires is due to the great quantities of litter which 

 accumulate during the process of natural thinning, and also, to a lesser extent, to the 

 character of the ground cover. Duff, or humus, is nearly lacking, except on a few of 

 the northern slopes, and plays no particular part in the spread and intensity of the 

 fires. The general ground cover consists of moss, usually a thin layer 2 or 3 inches 

 in depth, a slight sprinkling of pine needles, low shrubs, mostly species of huckle- 

 berry, and more or less of a grassy turf or sward. During the dry season all this 

 material burns readil3% but does not make a hot or high flaming fire. It is different 

 with the litter. The great mass of dry or partlj'^ dry wood of which it is composed 

 makes hot and flaming fires, consuming or killing all live timber. The litter is 

 derived in part from unconsumed debris left behind after previous fires, and in part 

 from trees killed by excessive stockage and consequent overcrowding. The dense 

 stockage is a sequel to fires and one of the phases of reforestation. When a 

 tract of forest situated below the upper subalpine areas between the 8,000 and 6,500 

 foot levels is destroyed by fire lodgepole pine almost always follows as the primary 

 restockage in at least 98 per cent of the cases. It is always set exceedingly close, 

 having 10 to 20 seedlings to a square foot of ground in favorable situations. The 

 close-set trees develop long, slender shafts, and as the stand becomes older the natural 

 process of thinning begins. The final result is that when the stand reaches 80 to 

 100 j'ears in age it is filled with long, slender dead trees, and is a veritable tinder 

 box. Most of the stands of the ages mentioned are choked with such accumula- 

 tions of dead and fallen timber. Further additions to the inflammable material are 

 furnished by the wreckage of the former forest, as often in a forest through which 

 fire has run there is left standing a mass of seasoning timber, although every tree 

 may be killed. Gradually the fire-killed trees are thrown down by the wind, 

 forming great tangled masses of. kindling wood for future fires to feed on. All 

 of the destructive fires of recent years appear to have originated, or at least to 

 have gained headway, in the debris that litters the close-set lodgepole-pine stands, 

 and as these constitute the great mass and hence the most valuable portions of the 

 forest, they need to be particularly guarded. 



RESTOCKAGE. 



In the subalpine areas young growth is almost everywhere scanty, whether 

 as restockage after fires or as the ordinary renewals in the growing forest. The 

 grassy openings made by fires during the Indian occupancy are very slowly giving 

 way to a young growth of spruce and white-bark pine. A potent cause for the 



