286 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 13 



has been differently affected, owing to the nature of the topography, 

 the variations in climatic conditions, and the various degrees of human 

 interference. 



Varied as are the different islands in topography and climate, they 

 possess certain basic similarities in the distribution and the aspects of 

 their plant communities. The western slopes of all the islands, except 

 San Nicolas where barren sand dunes prevail, are covered with grass- 

 lands, maritime scrub, or a low atriplex association. The eastern and 

 northern slopes of the larger islands are quite generally covered with 

 chaparral, savannas, or scattered areas of woodland. The canyons, 

 which afford protection from the wind, have much the same vegetation 

 types as are found on the northeastern slopes. Plates 5 and 6 afford 

 characteristic views of these northeastern slopes. In this section the 

 distribution and the floristic composition of these communities, as they 

 now exist, will be considered. 



Woodland Comm unties 



The woodland area on Santa Cruz is located on the main northern 

 ridge which rises to a height of 732 meters (2400 feet), while the 

 major part of the ridge is over 610 meters (2000 feet). This elevation 

 is sufficient to bring a heavier annual precipitation to Santa Cruz than 

 on any of the other islands.''' The prevailing winds, which are from 

 the northwest on San Miguel, have veered to follow the Santa Barbara 

 Channel and are nearly due west. As the main ridge runs slightly north 

 of west, the slopes are protected from the winds as well as from the 

 more direct rays of the sun. Thus, to judge from the evaporation data 

 secured on Santa Barbara Island, the evaporation rate should be not 

 more than 80 per cent of that on the southern slopes. The woodland 

 is composed mostly of closed cone pines intergrading between Pinus 

 muricata and Pinus remorata, with scattered groves of Lyonothamnus 

 floribundus asplenifolius and Quercus tomentella. In the more open 

 sections of this woodland there is a lower layer of arborescent forms of 

 Photinia arbutifolia, Prunus Lyonii, Cercocarpus betuloides, Arcto- 

 staphylos diversifolia, and Ceanothus arboreus. The closed cone pines 

 are dominant on the higher parts of the ridge while broadleaved 

 sclerophylls are relatively abundant on the lower slopes near the sea. 

 This is particularly true of the dissected remnants of a marine terrace 



"^In conversation with the caretaker on Santa Cruz April 13, 1941, the 

 writer was shown the daily records of precipitation for that year, beginning with 

 January 1, 1941, a total of 52.50 inches. No more records are available. 



