268 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 13 



northern islands, is usually combined with, or replaced by Siiacda. A tri- 

 plex, Lotus, Opuntia, Aplopappus, Astragalus, and other low herbs 

 and semi-shmbs. Native annuals and geophytes are also abundant in 

 all of the uplands, and in the gently sloping areas where they have not 

 yet been displaced by exotics or destroyed by erosion. It seems probable 

 that this type of vegetation must formerly have extended into many 

 areas which are now occupied by introduced grasses and forbs. 



Even if there had been no overgrazing on the islands, it is probable 

 that great change in the plant communities would have been brought 

 about by the introduction of exotic plants. Braun-Blanquet (1932) 

 states that geographic and climatic isolations are essential for the pre- 

 servation of relict plant communities, saying: ''They are ill adapted 

 for combat with the ubiquitous immigrants brought in everywhere by 

 cultivation." While there has been little cultivation on any of the 

 islands, the mere occupation by modern man has inevitably brought 

 about this immigration. 



There is little evidence to indicate any considerable changes in these 

 areas now occupied by woodland, by chaparral, or by coastal sagebrush. 

 However, it is probable that woodland may originally have extended 

 into some of the areas now occupied by chaparral. Since San IVIiguel 

 originally possessed considerable chaparral of the island type, which 

 is more susceptible to browse, it may be considered probable that certain 

 western upland areas of other islands, where the evidences of erosion 

 from destructive overgrazing are present, may once have been occupied 

 by chaparral. It is also possible, in this connection, that, as destructive 

 overgrazing was discontinued on Anacapa, Santa Cruz, and Santa 

 Catalina from thirty to forty years ago, badly eroded land may sub- 

 sequently have been reclaimed by the dense gro^^th of introduced grasses 

 and forbs. 



Ill Santa Barbar„\ Island 



Although observations of various environmental factoi-s had already 

 been made on all of the Channel Islands during the course of the Los 

 Angeles Museum Channel Islands Biological Suney it was desirable 

 that detailed measurements of certain ecological factors should be made. 

 Extended instrumental work could not be carried out on each of the 

 islands because of the large area involved and the difficulties of trans- 

 portation. Therefore it seemed desirable to select one island for this 

 objective study, one so situated that conclusions reached on it might 

 be more or less applicable to the other islands. 



