276 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 13 



This effort may affect the biotic balance to the detriment of the vegeta- 

 tion, especially as the rabbits and mice have few other enemies. 



Man's activities have favored the establishment of the exotic plants. 

 In 1918 nearly the entire island was burned over and both east and 

 west terraces placed under cultivation. As a result the indigenous plants 

 are to be found mainly in the shallow soils and on the steep seaward 

 slopes. Rocky areas on the western terrace and about the headlands, 

 the section of the eastern terrace cut by canyons, and parts of the central 

 ridge, also harbor many native plants together with the aggressive 

 foreign species. Introduced grasses, with Mesembryanthemum and Atri-- 

 plex semibaccata, have appropriated most of the area formerly under 

 cultivation, which was the most fertile part of the island. However, at 

 the present time, some of the natives, such as Coreopsis, Lycium, Suaeda, 

 Brodtaea, and Chenopodium calif ornicum are at least holding their own 

 against the exotic competitors. The smaller annual plants cannot as yet 

 compete successfully with the introduced Hordeum, Avena, or Mes- 

 embryanthemum, 



As springs, streams, lagoons, or marshes are entirely absent, no 

 hydrophytes, except those of marine habitats, are present. Due to the 

 fact that the few narrow beaches are wave-washed at the periods of 

 spring tides, and are colonized by the California and the Stellar sea 

 lions and an occasional sea elephant, no plant life is to be found on them 

 at the present time. However, Oenothera cheiranthijolia, a typical beach 

 plant, has been reported from the island by Hemphill (Jepson, 1925). 



Plant Communities 



This small island does not present the varied topography of such a 

 larger one as Santa Cruz. No habitat on Santa Barbara is as much as 

 a half mile from the sea, and the highest elevation is but 200 meters 

 (635 feet). The limited number of species on a small island cannot 

 give a great floristic complexity. Thus, there are no chaparral shrubs 

 and trees ; neither are there dune or riparian communities. However, the 

 variations in slope, exposure, and soil are as great as on any of the 

 Channel Islands. The habitats which are present on Santa Barbara 

 can be compared later with similar ones on the other islands, even 

 though on Santa Barbara but few species of the noiTnal plant com- 

 munity for that habitat may be present. Because of the essential simplic- 

 ity of the environmental pattern of Santa Barbara any differences be- 

 tween habitats would be less than the more sharply differentiated en- 

 vironments on the large islands. The general topography of Santa Bar- 

 bara and the distribution of its plant communties is shown in figure 8. 



