NO. 3 dunkle: plant ecology, channel islands 285 



Factors in Plant Distribution 



In addition to the edaphic factors which affect the environment of 

 the island communities there are also other relationships which should 

 be noted. 



Opuntia littoralts occurs in moderately extensive colonies on the 

 south exposures of the canyons, and on the southwest slope where the 

 main western terrace falls away to a narrow arm of the low western 

 terrace. In such localities it closely resembles Opuntia associations of 

 most of the other islands, such as the Opuntia-Encelia- A triplex associa- 

 tion on the steep southern slope of Anacapa. 



Many of the island plants have a high frequency while others possess 

 marked fidelity. Hordeum is to be found in every section of the island 

 though dominant only in fine soil where there is also a moderate ex- 

 posure to wind. Other exotics which are widely distributed are Malva 

 parviflora, which has even been recognized on the inaccessible stack 

 off the western end of the islands, Sonchus oleraceus, Chenopodium mur- 

 ale, Erodium cicutarium, Mesembryanthemum nodiflorum, M. crys- 

 tallinum, Silene gallica, and A triplex semihaccata. Of the native plants 

 A triplex calif ornica is to be found in every sea bluff community. A- 

 chillea also occurs in many such communities, particularly on the precipit- 

 ous northern clifiFs, as well as in different parts of the terraces. Coreop- 

 sis has been mentioned as occurring in every community which is not 

 subject to the more intense winds. On the other hand. Astragalus, Baeria, 

 and Malacothrix show a high fidelity to areas of severe winds. A few 

 plants as Lotus, Echeveria, Perityle, and Muhlenbergia appear to be 

 limited to southern southeastern, or southwestern slopes. A few plants, 

 such as Aphanisma, Flatystemon, Poly podium, Gilia, and Pterostegia, 

 are apparently confined to the northern and northeastern areas. 



Seasonal aspects consist mainly of green vegetative growth in winter, 

 the spring season of flowering, and the dry brown foliage of summer and 

 fall. However, Echinocystis blooms during the winter and Eriogonum 

 during the early autumn, while the prostrate form of Hemizonia may 

 withhold part of its blossoming until late summer. 



IV Plant Communities of the Islands 



It has been stated earlier in this paper that the original vegetation 

 of the Channel Islands has been greatly aflected by the activities of man. 

 The agencies put into play by such activities have destroyed or markedly 

 aflEected the indigenous communities over large areas. Each of the islands 



