NO. 3 DUNKLE : PLANT ECOLOGY, CHANNEL ISLANDS 275 



periods of heavy rainfall, such as occurred during the winter of 1940- 

 1941. While the actual record of the most sheltered rain gauge was 

 18.83 inches for 1940-1941 and 6.38 inches for 1941-1942, these figures, 

 on account of evaporation and overflow, are probably considerably less 

 than the actual precipitation. The average annual precipitation should 

 lie between that of the San Nicolas figure of 11.08 and the Santa 

 Catalina figure of 13.35. The recorded average of Santa Barbara for 

 the two wet years of 1940-1942 was 12.60 inches, and an empirical 

 estimate of the ten-year average precipitation might be about 12 inches. 



Figure 7 shows the results of over two years of instrumentation 

 at the east bluff station. 



In figure 7 it is noticeable that there is a fairly close correlation 

 between wind velocity, maximum temperature, and evaporation rate. 

 During the winter the wind graph shows an increase over the normal, 

 but follows the graph of the evaporation rate very closely during the 

 remainder of the year. The convergence of the graphs for the black-cup 

 and the white-cup evaporation rates is of seasonal rather than insular 

 significance. The rise of the evaporation rate in spring and fall is quite 

 in harmony with previous observations in respect to drying, east winds 

 during those seasons. There is normally much fog during the summer, 

 as hygrograph records show. Both wind and sunshine are more prevalent 

 during spring and fall. 



BiOTic Influences 



Although this little island has not been inhabited continuously for 

 many years and is not easily accessible it has many evidences of man's 

 visits. It has been used as a base for otter hunting, for lobster fishing, 

 and for farming operations. The writer has talked with various indivi- 

 duals who have built cabins there and have tried to fill in unfavorable 

 fishing seasons by desultory farming. It is remarkable how much human 

 activity has been centered about this tiny island and how quickly time 

 and storm have erased most of the visible handiwork. Yet the indirect 

 influences of man will affect the island for years to come. 



Twenty species of exotic plants have been introduced and now 

 dominate large sections of the island. Cats and rabbits also have been 

 introduced. The cats have been able to keep the rabbits in check so 

 that they have made no serious inroads upon vegetation, as they have 

 on the eastern island of Anacapa. White-footed mice are the only native 

 land mammals. A recent effort has been made by the National Park 

 Service to reduce the cat population in order to protect nesting birds. 



