318 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 13 



Coreopsis has very finely divided leaves which wither at the beginning 

 of the dry season, while Lavatera has thin, broad, simple, ever-green 

 leaves. Quercus tomentella, Quercus MacDonaldii, Ceanothus arboreus, 

 Prunus Lyonii_, and Dendromecon Harfordii have leaves somewhat 

 larger than those of related mainland species. The larger leaves of these 

 insular endemics are also reminiscent of a warmer and more moist 

 condition in the past. 



Chaparral 



The chaparral, except for that of the warmer, interior slopes of 

 Santa Cruz, differs from most of the mainland chaparral in its com- 

 parative size. Brandegee (1888) has stated that many shrubs of the 

 mainland become arborescent on the islands, apparently owing to effects 

 of the moist sea breezes. The lower evaporation rate, caused by the 

 higher humidity and the lower summer temperature, in places sheltered 

 from the stronger winds would undoubtedly tend to make for a longer 

 growing season. Furthermore, the possibly greater freedom from fires 

 would result in greater longevity. Quercus dumosa becomes decidedly 

 arborescent on the islands, growing into small trees which may reach a 

 height of ten meters (33 feet) in favorable localities. Photinia ar butt- 

 folia and its two varieties, Cercocarpus betuloides and its three varieties, 

 Sambucus coerulea, Arctostaphylos diversifolia, Ceanothus megacarpus, 

 and Rhamnus crocea insularis are usually arborescent. Many other 

 shrubs, such as Rhus laurina, Rhus integrifoliaj Malvastrum fascicu- 

 latum, and Prunus ilicifolia are very frequently arborescent in form 

 if not in size. Browsing by goats and self-pruning resulting from light 

 deficiency for the lower branches are two of the factors which may 

 contribute to this arborescent form. 



On the three larger islands Quercus tomentella, Lyonothamnus 

 floribundus, and L. floribundus asplenifolius develop into trees which 

 may reach fifteen meters (50 feet). On San Clemente Lyonothamnus 

 rarely exceeds ten meters (33 feet), and on Anacapa Quercus is rarely 

 over six meters (19 feet) in height. On these smaller islands there is 

 less protection from wind as well as a lower annual precipitation. 



The average (fire-type) chaparral on the mainland varies from one 

 and one-half to two meters (5 feet), with Adenostoma and Photinia 

 up to four meters (13 feet) (Cooper, 1922). This agrees with the 

 average height of the chaparral on the southern ridges of Santa Cruz. 

 There is a tall, "unburned" chaparral in favorable locations in the 

 mountains of southern California and northern Baja California. In all 



