LIFE ZONES OF CARLSBAD REGION 11 



sun's rays and heat, and the steeper cold slopes 

 (northern exposure) being more completely cut off 

 from light and heat. On opposite sides of high ridges 

 or deep canyons running in a general east and west 

 direction there is often a difference of one thousand 

 feet in the zone levels on slopes facing north or south, 

 as shown by the plant and animal life. These differ- 

 ences are due to actual differences in temperature, as 

 may be seen where the snow lies long on north slopes 

 and disappears quickly on south slopes. The effect 

 of slope exposure in this region of ridges and canyons 

 must also be kept in mind to avoid confusion in regard 

 to the distribution of species, and the extent of life 

 zones. It should also be noted that each zone blends 

 into the others and is nowhere sharply defined or 

 bounded by a line. 



The Lower Austral zone is here clearly marked by 

 such characteristic shrubs as the creosote bush, mes- 

 quite, Acacia constricta, ocotilla, allthorn, blue- thorn, 

 desert willow, three-leaved barberry, small-leaved sumac, 

 green sumac, Mexican buckeye, varnish bush, and 

 Baccharis; by lechuguilla, sotol, large-fruited yucca, 

 narrow-leaved yucca; and by numerous species of cac- 

 tuses, many small plants, and grasses. 



While the plants are the most conspicuous and con- 

 venient indicators of the life zones, the native mammals, 

 birds, and reptiles are equally characteristic. In the 

 Carlsbad Cave region, the Lower Austral zone is 

 characterized by the Texas jack rabbit, desert cotton- 

 tail, Rio Grande striped ground-squirrel, cave mouse, 

 gray wood rat, cotton rat, large and small kangaroo 



