THE " 

 POPULAR SCIENCE 

 MONTHLY. 



NOVEMBER, 1914 



TREE DISTRIBUTION IN CENTRAL CALIFORNIA 



By Dr. W. A. CANNON 



DESERT BOTANICAL LABORATORY 



IT has frequently been observed that the shrubs in dry regions occur 

 isolated from one another, with the effect that the landscape as a 

 whole has a spotted appearance. This in certain regions is very striking. 

 For example, on drainage slopes or bajadas of the mountains of southern 

 Arizona or southern California, one sees a discontinuous vegetal cover- 

 ing, conveying the idea that there are more plants than is actually the 

 case. The remote cause of the sjDarseness of such plant covering, as is 

 well known, is to be traced to a precipitation amount which is inadequate 

 to support a dense shrub population. The immediate cause, however, is 

 to be sought in competition between plants for ground water. The 

 roots of neighboring plants intermingle and lie in the same soil hori- 

 zon, seeking the same soil moisture. Such shrubs as have the most 

 efficient root system, either as seedlings or mature forms, survive. 

 Thus, here, as elsewhere in nature, the victory is to those which are 

 best adapted to the particular environment. 



As one leaves such marked arid regions behind, and journeys to 

 regions which are less arid, as in the valleys of Central California, the 

 interrupted distribution of the shrubs gives way to a dense shrub popu- 

 lation, the chaparral, or pygmy forest. But in this portion of California 

 one finds trees growing in open forests with park-like effect, in a 

 manner exactly comparable to the open stand of the desert shrubs. 

 This observation applies to the valley floors or the lower slopes of the 

 mountains or low hills. In the more moist regions, as in the mountains, 

 forest covering may be relatively, or actually, dense. Also the species 

 to which the observation applies are, in the main, oaks. It will be shown 

 in this note that the three species of oaks especially spoken of will have 

 each a different and characteristic distribution and will have a different 

 and characteristic relation one to another. It will also be shown tha 4 : 

 these are in part dependent on the character of the root-systems of the 



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