NO. 3 dunkle: plant ecology, channel islands 295 



ranges of temperature are very small. The pounding of the surf makes 

 the air and the soil decidedly saline. Nevertheless the wide variety of 

 edaphic and orographic conditions usually prevents any one plant, or 

 combination of plants, from being dominant over any extensive area. 

 The communities can be treated conveniently by the relation of their 

 slope exposures to wind and sun. 



The sun is the most powerful factor on southern exposures, so that 

 the evaporation rate here is relatively high. Owing to the steepness of 

 the slope, which causes a high run-off of precipitation, and the high 

 evaporation rate, there is more bare soil and rock than there are plants. 

 The aspect of these slopes from the sea has led many casual observers 

 to conclude that the islands are mostly desert. 



The western exposures are influenced by the prevailing winds and 

 are of three types: low headlands where there is a decidedly saline 

 influence, high rocky ridges, and high rounded bluffs where the soil 

 is deeper and of somewhat finer texture. The low headlands are marked 

 by Atriplex and other low mat-like plants of rather drab appearance. 

 The rocky ridges are covered with foliose lichens where the wind 

 ascending the slope is frequently laden with condensing moisture. Many 

 of the niches between the irregular blocks of rock are occupied by low 

 shrubs, semi-shrubs, and perennials. On the high, rounded bluffs low 

 annuals such as Baeria and Malacothrix form veritable carpets of green 

 and gold in the spring, interspersed with matted perennials like Astra- 

 galus, Hemizoniaj and Aplopappus, 



The north and east exposures, which are sheltered from the wind 

 and the more direct rays of the sun, are in sharp contrast to other 

 slopes. There is usually a luxuriant growth of grasses, ferns, clovers, 

 and other forbs, suffrutescent perennials, and low shrubs. These remain 

 green and in bloom until mid-summer. One of the best developed ex- 

 amples of this Eriogonum-Eriophyllurn association is on the long, north- 

 eastern, talus slope of the western island of Anacapa. Here the suffru- 

 tescents and forbs form a tangled mat, through which one may proceed 

 only with diffculty. A section of this long slope is illustrated in plate 18. 



Shrubby lupines are on all the islands except Santa Barbara, but 

 the variation in species is great and their different characteristics so 

 interwoven that positive identification is yet uncertain. These are ap- 

 parently varities of an original parent stock which has been differenti- 

 ated into geographic races. The variable characteristics resemble those 

 of the closely related mainland species but are combined into different 

 patterns in the insular races. So confused is the nomenclature that five 

 different names have been applied to plants of a single colony. With 



