Rydberg: Phytogeographical notes 15 



therefore offering little resistance to the wind. The branches are 

 short, slender and dcflexed, therefore well adapted for shedding 

 the falling snow. It is, hence, very well adapted to the severe 

 climate of the mountain peaks. At the timberline it, as well as 

 Abies lasiocarpa, becomes stunted, low, with the lower branches 

 enormously elongated and closely pressed to the ground. The 

 Engelmann spruce is a slow grower, naturally so on account of the 

 poor and rocky soil and the severe climate. On a stump from a 

 tree cut in the La Sal Mountains, measuring 26 inches, I counted 

 over 260 annual rings. In very favorable conditions it may reach 

 a height of 120 feet and a diameter of about 3 feet. 



Next to the Engelmann spruce, the Aspen is the most common 

 tree in the Subalpine region of Colorado. It grows on both 

 slopes, usually in groves, but sometimes mixed, and usually 

 prefers rich soil. After the spruce wood has been destroyed by 

 forest fires, it often takes possession of the ground, as its seeds 

 germinate more quickly and it is a faster grower. It reaches its 

 best development along streams and in spring^' places. It is 

 seldom found up to an altitude of more than 11,000 feet and its 

 height is seldom over 25 or 30 feet in this region. 



The Fox-tail Pixe, range pine, or prickle-cone pine, Pinus 

 aristata, is the chief tree of the southern slopes of the Southern 

 Rockies. It is not found in the Northern Rockies at all, but 

 exists in the mountains of the Great Basin and in the southern 

 Sierra Nevada. It is a bulky tree, branched usually near the 

 base. In favorable situations it sometimes reaches a height of 

 50 feet, with a trunk 3 feet in diameter. Near the timberline 

 it becomes very gnarled, crooked, and twisted, with the branches 

 short and few on the windward side and unproportionally de- 

 veloped on the leeward one. It never forms the depressed 

 cushion-like or sugar-loaf-like growth of Picea Engelmannii or 

 Abies lasiocarpa in similar situations. Pinus aristata is a char- 

 acteristic tree of the Sulbapine Zone, only rarely found in the 

 Montane Zone as low as 8,000 feet. If found there it grows 

 mostly with Pinus flexilis, as it does sometimes in the Subalpine 

 Zone. 



The fourth of the trees of the Subalpine Zone is the Subalpine 

 Fir, Abies lasiocarpa. It usually grows scattered among Picea 



