22 ABSAROKA DIVISION OF YELLOWSTONE FOREST RESERVE. 



small stands of pure growth while in the sapling stage, and in more or less mixed 

 stands as mature age is reached. Lodgepole pine is its most common associate in 

 the mixed stands, with lesser proportions of Engelmann spruce, the red fir in such 

 situations forming from 15 to 30 per cent of the stand. 



The subalpine fir occurs most abundantly in the lower areas of the subalpine 

 forest. It is always set in mixed stands where it seldom or never exceeds 15 to 28 

 per cent. 



The Engelmann spruce is found abundantly throughout the reserve. While the 

 species here properly belongs to the subalpine-forest type, it occurs lower than 6,000 

 feet, following the streams in their downward course almost into the plains. In the 

 subalpine forest the spruce commonly occurs in mixed stands and forms from 16 to 

 45 per cent, occasionally rising to 75 per cent, of the growth, as in the lowest areas 

 of the subalpine forest in the eastern tracts of Hell Roaring Creek Basin. "Where 

 the percentage of the species runs high it is always set in old-growth stands. 



The composition of the forest is neither normal nor ultimate, but represents a 

 'transitional phase due to the numerous fires which have devastated the region 

 for centuries, particularly during the last 200 years. The lodgepole pine is most 

 numerous because here it is a more abundant seed producer, and is better able 

 toadapt itself to the changes in soil and moisture ratio, and probably in chemical 

 composition of the soil caused by the fires. Burned stands, composed in part of red 

 fir and in part of Engelmann spruce, have been replaced by lodgepole pine in areas 

 where it originally formed only a comparatively small percentage. As the lodgepole 

 pine reaches .maturity and the stands become more open through natural thinning it 

 will, in course of time, be largely displaced by red fir and spruce. 



In the subalpine zone the composition of the forest is more nearly normal than 

 in the areas in which lodgepole pine prevails. The fires have here reduced the 

 percentage of Engelmann spruce, but have not favored the increase of other species, 

 as the burned areas are either grassy or unforested, and the spruce is slowly spread- 

 ing and eventually, when fully established, will greatly exceed its present percentage 

 in the subalpine forest. 



AGE AND SIZE OF TREES. 



The greatest diversity prevails in the ages of the trees. Stands 15 to 20 years 

 old are associated with growths 75 to 100 years of age and with veteran stands 200 

 to 300 years old. This condition has been brought about by fire, the different ages 

 marking burns of different periods. Of the entire forest below the subalpine 

 zone 10 per cent is less than 50 years old, 50 per cent more than 50 and less than 

 120 years, while the remaining 40 per cent comprises veteran stands from 120 to 

 300 years of age. 



