

LIFE ZONES 



307 



in life on the western and eastern slopes can tell what effect a 

 mountain may have in the distribution of a given kind of plant 

 or animal. Living things on one side of that range are quite 

 different from those on the other. Natural barriers may be 

 mountains, deserts, large bodies of water, and even rivers. Climatic 

 conditions, especially, limit the range of plants, which cannot 

 endure great differences in rainfall, in temperature, humidity, 

 wind, or sudden atmospheric changes. Some plants and animals 

 have special adaptations which enable them to cover large areas, 

 such as parachutes on seeds 

 and the wings of birds. For 

 such plants and animals the 

 geographic range will be 

 greater than for less favored 

 forms. 



Life zones. Reference has 

 already been made to the 

 fact that a zonal distribu- 

 tion of plants and animals is 

 easily seen in climbing any 

 high mountain. Any area 

 in which most of the plants 



Or animals belong tO Single Zonal distribution of plants on a mountain 

 , , . , „ „ rising from a desert in Arizona. Give cause for 



Or relatively tew groups Of different zones. 



plants and animals is called a 



life zone. Life zones are often rather sharply marked, but usually 

 show transitional areas between them. A region which has been 

 carefully studied and which shows this zonal distribution in a 

 marked way is the San Francisco mountain region in north 

 Arizona. Here a mountain nearly 13,000 feet in height rises 

 out of a desert plain. This mountain shows successively two types 

 of desert zone, a lower and upper, each with its own desert fauna 

 and flora, cactuses, sagebrush, a few birds, mice, lizards, and snakes. 

 Then a' region at between 6000 and 7000 feet of pinon pines and red 

 cedars, inhabited by more birds and a few mammals. Between 

 7000 and 8200 feet we find forests of Douglas and balsam fir, with 

 such mammals as meadow mice, chipmunks, deer, lynx, and puma. 



