LIFE AREAS 283 



Life Areas of California 



Most people who have ascended mountains, on business or 

 for pleasure, have noticed that there was a gradual change in the 

 trees and other vegetation as height was gained, and some see 

 that there is a system in this change. At a certain height in one 

 motintain occurs a combination of trees, shrubs, plants, birds, in- 

 sects and mammals, which combination is repeated in a general 

 way on other mountains at a similar altitude, modified by local 

 causes, such as soil, angle or direction of slope, nearness or remote- 

 ness of large bodies of water, height above base level and other 

 conditions. Going higher, a change in the birds, trees, etc., oc- 

 curs through the gradual disappearance of some species and the 

 substitution of others until a new combination is formed. A sim- 

 ilar combination is repeated in other mountains of the region in 

 about the same order. Local causes modify these repetitions more 

 or less, but the general similarity is sufficient to force the close 

 observer to the conclusion that they are controlled by general nat- 

 ural laws. Within a few years much study has been given to^ the 

 elucidation of these natural laws, and I will attempt to summarize 

 some of the results of these investigations in California. 



The causes controlling the geographical distribution of life 

 are many, the most important being temperature, moisture, soil 

 and light. We are accustomed to sum up three of these leading 

 causes in the word climate. 



The most important single cause of the varied distribution of 

 life is heat; its quantity and daily and yearly range over a given 

 area. Other conditions being equal, the warmer the climate of a 

 locality is, the more luxuriant and varied it forms of life will be. 

 A great yearly or daily range of temperature unfavorably affects 

 the life of an area by weeding out the forms most sensitive to such 

 changes, on the principle of the "survival of the fittest." 



The heat of a locality is affected by its latitude, altitude, direc- 

 tion of the prevailing winds, height above base level and slope ex- 

 posure. Increase of latitude and altitude produce similar climatic 



