NO. 3 DUNKLE : PLANT ECOLOGY, CHANNEL ISLANDS 257 



However, the low summer temperatures, the high relative humidity, 

 and the great amount of fog or low stratus, give an effectiveness to 

 the annual precipitation well above that of an eleven inch precipitation 

 inland. It is true that on southern slopes, with the high angle of the 

 sun, the shallow soil, and the high wind velocity produce xeric condi- 

 tions which have misled casual observers as to the true climatic status 

 of the islands. The general physiognom.y of the vegetation, its density and 

 its floristic composition, do not fit the definition of a desert. Only on 

 the southern end of San Clemente does the physiognomy of the vegetation 

 approach that of a desert. 



Mariti?ne climate. Thus it is seen that the islands have the dry 

 summers, the humid-temperate winters, and the characteristic vegeta- 

 tion of the Mediterranean climate, and the incipient trade winds of 

 summer, supplemented by intermittent westerlies in winter, with some 

 modifications; i.e., uniformly low ranges of annual and diurnal tempera- 

 tures, high average of relative humidity, considerable low stratus or fog. 

 These latter features are characteristic of an oceanic climate. This 

 type, in contrast to the continental climate, has long been recognized by 

 geographers. That a sub-type of oceanic climate is typical of windward 

 coasts in the low latitude temperate windward coasts of the temperate 

 zones has also been established, and the terms "oceanic," "littoral," and 

 "coastal" have been applied (Blair, 1941), (Salisbury, 1931). Inasmuch 

 as the flora of the Channel Islands is sufficiently distinctive to have led to 

 its classification as one of the primary divisions of the "Nearctic" region 

 (Leconte, 1888), its climatic distinctiveness should be adquately recog- 

 nized. The controlling factor of the insular climate lies in the narrow 

 range of annual and diurnal temperature. There is a difference of less 

 than 10° C. (18.0° F.) between the January and the July mean temper- 

 atures. Indeed, for the islands themselves no annual range of more than 

 6.3 ° C. ( 1 1 . 1 ° F. ) has yet been reported. 



Additional characteristics of the insular climate shows also the fol- 

 lowing characteristics: (1) a mean noon relative of over 60 per cent, 

 (2) a mean July temperature of less than 22° C. (71.6° F.), (3) an 

 aridity coefficient of 12 per cent or less (Gorcznsky, 1940), and (4) 

 night or morning low fog or stratus for the greater part of the year. 

 Accordingly the term "Mediterranean maritime" is proposed, though 

 for the purposes of this paper the term "maritime" will be used to 

 designate the climatic type of the insular area and of the immediately 

 adjacent mainland coast. The data for computing the annual range 

 of temperature together with the average precipitation, are given in 

 table 2. 



