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TEXTBOOK OF BOTANY 



Douglas fir cover by far the largest areas. The western yellow pine 

 occurs in open stands alone, or associated with other conifers, from 

 the eastern slopes of the Cascades, the Sierras, the Columbia basin, 

 the lower elevations of British Columbia southward in the Rockies 

 to the Arizona Plateau and the mountains of Texas. It occupies 

 rather drv sites in regions with 20 to 30 inches of rainfall adjoin- 

 ing grasslands, chaparral, oak scrub, or the dry pifion-juniper wood- 

 lands. 



Fig. 410. Mature western yellow pine {Pimis ponderosa) , Eldorado National Forest, 

 California. Photo bv U. S. Forest Service. 



At its northern limit the \ ellow pine occurs at elevations up to 3000 

 ft., and in Arizona and New Mexico, 6000 to 8000 ft. In the Sierras on 

 cool and moist slopes it is associated with Douglas fir, sugar pine, and 

 incense cedar. The mixed forest of pine and fir occurs in the Sierras up 

 to 5500 feet and at from 6000 to 9000 feet in the central Rockies. Forests 

 predominantly of Douglas fir occur at somewhat higher elevations. In the 

 northeni Rockies the western larch, the western white pine, and the 

 lodgepole pine may occur with Douglas fir in varying proportions. The 

 lodgepole pine is a pioneer tree that invades burned-over lands at all 

 levels from the dry yellow pine belt at low elevations through the belts 



