LIFE AREAS OF CALIFORNIA 
BY 
FRANK STEPHENS 
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 mountain occurs 
a combination of trees, shrubs, plants, birds, insects 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 remoteness of large bodies of water, 
height above base level and other conditions. Going higher, a change 
in the birds, trees, etc., occurs through the gradual disappearance of 
some species and the substitution of others until a new combination is 
formed. A similar 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 natural 
laws. Within a few years much study has been given to the elucida- 
tion 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 its forms of life will be. A great 
