78 CARNEGIE INSTITUTION OF WASHINGTON. 



identical physical conditions, or whether dissimilarities of soil texture 

 and conditions of soil aeration are closely correlated with those of the 

 plant covering. The fact that the Avra Valley is not undergoing the 

 normal course of physiographic development, but is subject to frequent 

 checks or reversals of such development, makes it a particularly 

 suitable area for an investigation of this problem. 



Geobotany of the Santa Lucia Mountains, hy Forrest Shreve. 



A reconnaissance has been made of the vegetation of the Santa 

 Lucia Mountains, which skirt the coast of the Pacific Ocean between 

 Monterey and San Luis Obispo, California. The physical conditions 

 of the region are dominated by the rainless summer, which is charac- 

 teristic of the entire Pacific Coast, and by the proximity of the sea. 



The region is like many other Calif ornian areas in having a very 

 dissimilar series of vegetations growing in close proximity. Among 

 these are: (a) grassland, embracing many annual and root-perennial 

 plants; (h) open oak forest, usually superposed upon the grassland; 

 (c) closed oak forest, with abundant shrubbery; (d) redwood forest, 

 with characteristic accompanying trees and shrubs; (e) chaparral, 

 varying greatly in composition and vegetative characteristics. The 

 most xerophytic of these vegetations is the grassland, which is found 

 in the valleys and on the detrital slopes and hills of the landward 

 side of the mountains. In a number of localities it is found to dominate 

 all situations without regard to topographic or soil differences. The 

 most hygrophytic of the vegetations is the redwood forest, which 

 occupies only the seaward valley-bottoms and slopes, usually where 

 it is subject to frequent visitation by fog. 



The chaparral varies in density, height, and composition, but in 

 some one of its many forms it is the most ubiquitous of the vegetations. 

 The most xerophytic forms of chaparral are composed solely of Arte- 

 misia calif orriica or of Salvia mellifera, the former being commonest 

 in the interior, the latter on the seaward slopes. Adenostoma fasci- 

 culatum forms the most abundant type of chaparral in all parts of 

 the area, growing in pure stands more commonly than is true of the 

 other chaparral shrubs. Arctostaphylos is dominant mainly on sand- 

 stone rock or sandy soil, or at high altitudes, often growing with 

 Ceanothus. The most hygrophilous types of chaparral are those made 

 up of species of Ceanothus, which usually reach a much greater height 

 than the other chaparral plants. This type is frequently invaded by 

 young oaks, Umhellularia, and Arbutus. 



The conditions determining the occurrence of grassland and of 

 redwood forest are rather obvious, but this is by no means true of the 

 types of chaparral mentioned and of several other less common ones. 

 Differences of elevation between sea-level and the highest peaks and 



