NO. 3 DUNKLE : PLANT ECOLOGY, CHANNEL ISLANDS 323 



included as all but one of the twenty-one introduced plants of Santa 

 Barbara are therophytes. Here also are none of the larger woody shrubs 

 or trees of chaparral and woodland. The small number of native species, 

 however, is fairly representative of the most extensive of the communities 

 of the other islands: i.e. the sea bluffs, the coastal sage brush, and the 

 suffrutescent-grassland community. 



The therophyte percentage for both native and exotic annuals is 

 60 per cent, which compares well with figures for various islands in the 

 Mediterranean Sea as reported by Raunkiaer (1934). The chamaephyte 

 and the geophyte percentages are also exceptionally large as should be 

 the case for a Mediterranean climate. The number of succulents is also 

 large, as would be expected in a dry maritime habitat. On the larger 

 islands the percentages would be slightly altered by the inclusion of many 

 more phanerophytes, yet the spectrum shown here would be roughly 

 typical of the wind-swept areas of all the islands. 



VII Conclusion 



The Channel Islands possess a flora that is distinctive and responsive 

 to the insular environment. Geologists have postulated, during past 

 epochs, the existence of a former land mass (Catalinia) which included 

 the area through which these eight islands are now scattered, and which 

 probably extended farther to the south and west. The evidence presented 

 by the distribution of the indigenous and endemic species of island plants 

 confirms the conclusion of a former common land mass. 



The geographic separation from the mainland, the distinctive climate, 

 and certain edaphic factors have brought about a rich endemic flora. In 

 addition many other island plants show minor variations in form. 



The direction of the prevailing wind gives an oceanic type of climate, 

 while the dry summers and mild, moist winters are characteristic of the 

 Mediterranean type. The maritime climate of the islands and of a 

 narrow coastal strip of the mainland may be divided into three types 

 upon the basis of the mean annual precipitation and certain characteristics 

 of the vegetation. The climate, subject to the interruption of intermit- 

 tent cycles, has gradually become drier since the Pleistocene epoch. 

 Tropical subsidence air causes excessively dry periods during the spring 

 and fall. 



The alkalinity of many of the island soils, the wind intensity, and 

 the long period of summer aridity have favored the development of 

 succulence and leaf pubescence. The moist, warm winters have probably 

 favored the development of suifrutescence in both herbaceous perennials 

 and shrubs. 



