4 2 



WILD FLOWERS AND TREES OF COLORADO 



are found at Colorado Springs and southward. The distribution of the 

 pinyon pine is similar. Many of the high-altitude trees extend far north 

 to British Columbia and even Alaska 1 . A considerable number 

 range to the Pacific coast, but only a few show a distribution far 

 eastward. 



Fig. 38. — Rock Pine, Growing in the Open, Estes Park 



Limits of tree distribution.— The upper limit of tree growth, or timber- 

 line, is variable as to altitude. On north exposures the trees do not 

 extend so high up the mountain side as they do on the warmer and less 

 windy south slope. Cold, wind and dryness all combine to limit the 

 upward extension of forests on mountains. At timberline are found 

 scattered clumps of wind-blown trees often contorted into fantastic 



