CYPRESS AND JUNIPER TREES OP ROCKY MOUNTAIN REGION. 25 



OCCURRENCE AND HABITS. 



In the United States mountain cedar forms very dense, pure, or 

 nearly pure, stands, sometimes of vast extent, as on the semiarid 

 limestone hills of the Edwards Plateau in central Texas. It usually 

 grows in dry rocky, gravelly, or sandy soils, often in crevices of 

 bare rock. Mountain cedar also grows both in pure stands and in 

 mixture with other species in lower, sheltered situations in deep- 

 washed soil of good quality. Interspersed with mixed stands are 

 often groups and scattered trees of one-seed juniper, Pinchot juniper, 

 Mexican walnut, live oak, Spanish oak, Durand oak, cedar elm, and 

 hackberry. The dense, sometimes almost impenetrable, stands of 

 this juniper on limestone are locally known as "cedar breaks." 1 



In this country mountain cedar occurs chiefly at elevations between 

 600 and 2,000 feet. Little is known of its range and habitat in 

 Mexico, where it is said to occur much more extensively and at 

 higher elevations than in the United States. 



Mountain cedar is very tolerant of dense shade during the seedling 

 and early sapling stages, as shown by the existence of extremely 

 dense thrifty stands. It appears to be much less tolerant later in 

 life, when its crown becomes thinner and more open (PI. XIV). 

 In ability to endure shade, however, it compares favorably with red 

 cedar (Juniperus virginiana) , but probably it would not maintain 

 itself under long suppression as does the latter tree. Local reports 

 of mountain cedar having come up on an area immediately after a 

 full stand of oak had been cut off give further evidence of its toler- 

 ance during early life, since on such areas it must have existed for a 

 number of years in a suppressed condition, and recovered when the 

 oak was removed. 



Mountain cedar bears seed abundantly, and reproduction is plen- 

 tiful in loose, permeable soils, and in broken, rocky formations, and 

 also in soil-filled pockets and crevices of bare rock. The sweetish 

 berries are eaten by birds, which assist greatly in a wide distribution 

 of the seed. 



LONGEVITY. 



Juniperus sabinoides is moderately long-lived, though the extreme 

 age attained is at present unknown. Trees from 5 to 7 inches in 

 diameter, on exposed, rocky sites, are from 150 to 180 years old, 

 while trees from 8 to 10 inches in diameter, in sheltered places on 

 deep, permeable, sandy or gravelly soil, where growth is most rapid, 

 may be only from 95 to 125 years old. Large trees occasionally 

 found in the driest situations are probably at least 250 years old. 



1 Popularly the allusion probably is to the fancied similar lowland "canebrakes," but properly this 

 name appears to refer to the physiographic nature of the plateau region in which dense growths of moun- 

 tain cedar occur. 



