38 BULLETIN 680, U. S. DEPARTMENT OF AGRICULTURE. 



supplies large quantities of telegraph and telephone poles, as well as 

 light-traffic railway ties and posts. 



OCCURRENCE AND HABITS. 



Western red cedar is confined almost entirely to regions of abun- 

 dant precipitation and atmospheric humidity, and chiefly also to 

 wet or constantly moist situations (Map No. 8). Occasionally, 

 however, it occurs on moderately dry slopes and warm exposures, 

 but here it is always stunted. In the Rocky Mountain region 

 western red cedar occurs mainly at elevations between about 2,000 

 and 7,000 feet, the largest and best-formed trees occurring below 

 5,000 feet, mostly small trees or shrublike forms being found above 

 this level. Only shrubby growths occur in the highest places. The 

 tree generally grows on moist flats, river bottoms, benches, gentle 

 slopes, in and about swamps and wet, springy places, and in cool, 

 moist gulches and ravines. Abundant soil moisture is on the whole 

 more important than quantity or quality of soil; both are, however, 

 essential for the best growth. Western red cedar forms dense pure 

 stands of only limited extent, the formation of small pure patches 

 and groups being especially characteristic. These growths are 

 usually interspersed or otherwise mingled with western hemlock, 

 Douglas fir, lowland white fir, western white pine, western larch, 

 lodgepole pine, Engelmann spruce, and western yew. Its most 

 frequent associates are lowland white fir and Engelmann spruce. 



Western red cedar is in general very tolerant of shade. This 

 quality varies, however, with age, altitude, latitude, amounts of 

 soil and atmospheric moisture, and climatic conditions. The tree 

 grows well in dense shade during seedling and early pole stages of 

 fife, and may even reach maturity and old age under constant shade ; 

 but rapidity and fullness of growth are retarded in proportion to 

 the density of shade; for although a high degree of shade is tolerated 

 without retarding growth during early life, it is not required in middle 

 and later fife. Tolerance is greatest under the best conditions for 

 growth and toward the lower limits of the tree's vertical range. 

 Here it maintains a dense crown cover throughout life and com- 

 monly forms an understory, alone or with lowland white fir, western 

 white pine, and other species. The density of pure (limited) stands 

 of seedlings and later young growths is so great as to exclude all 

 intolerant, and often some tolerant, associates. Compared in 

 tolerance with other conifers of its range, western red cedar ranks 

 with Tsuga mertensiana, Chamsecyparis nootkatensis, Picea engel- 

 manni, and Taxus brevifolia. 



Thuja plicata is a prolific seeder, specially heavy seed production 

 occurring at intervals of two or three years. The seed has a rather 

 high rate of germination but only transient vitality. It falls from 



