no. 3 dunkle : plant ecology, channel islands 263 



Destructive Grazing and the 

 Life Forms of Plants 



Other islands have suffered severely from erosion only in limited, 

 exposed areas, but the vegetation has generally suffered from the selective 

 grazing and browsing of various introduced animals. The island vegeta- 

 tion had, previous to the coming of the white man, been free from 

 grazing or browsing animals for an indefinite period in the past, as 

 there is no record or trace of any such animals since the Pleistocene, 

 until their introduction in the past century. It is highly probable that a 

 type of vegetation developed under such circumstances which would 

 have been impossible of development in the presence of herbivorous 

 animals. Certain individual species: Coreopsis gigantea, Lavatera assur- 

 gentiflora, Malacothrix saxatilis implicataj Ne?nophila racemosa, Erio- 

 phyllu7n Nevinii, Eriophylliim staechadifolium depressum, and Aplo- 

 pappus canus are examples of insular plants that are readily damaged 

 by grazing. This is implied by their tender, succulent nature; the lack 

 of ability to reproduce from adventitious buds; and by the fact that 

 they are now limited to inaccessible areas where grazing animals have 

 not been present. 



The destructiveness of grazing animals cannot be as well envisioned 

 by the near-extinction of a few species, as by their effect upon the vegeta- 

 tion as a whole. This may best be seen by comparing conditions on the 

 much grazed islands, such as San Miguel, San Nicolas, and San Cle- 

 mente with the conditions of little grazed areas such as that of the west 

 island of Anacapa, Santa Barbara, Prince, and Sutil islands, and Bird 

 Rock. One or more of the plant species just mentioned are abundant or 

 dominant on these small islands in habitats similar to habitats on the 

 other islands where none or few of these species can be found at present. 



Other animals than sheep or goats have been introduced on the 

 islands. Hogs have been on Santa Cruz for many years and on Santa 

 Catalina for at least ten years. A few rabbits are to be found on Santa 

 Barbara; and the eastern island of Anacapa is overrun with rabbits at 

 the present time, with consequent serious destruction of the native 

 vegetation. Rats have also been introduced on most of the islands. Deer 

 and bison have been on Santa Catalina for about fifteen years. Tule 

 elk, deer, and Siberian white deer have been on Santa Rosa since 1893 

 (Meadows, 1943). The long previous freedom from herbivorous animals 

 permitted the development of extensive and unique plant communities, 

 dominated by tender forbs and semi-succulent, suffrutescent shrubs. 



