THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 85 



present alternating southeast and northwest slopes, and there is 

 sharp vegetational alternation corresponding with the slope-exposure 

 differences. The first two species occupy the slightly moister north- 

 west slopes in relatively close formation, and the last two make a 

 sparse covering on the opposite hot, dry exposures. The alternation 

 is very conspicuous when viewed from a distance. There are thus 

 degrees of xerophytism among the coastal sagebrush species, giving 

 rise to additional successional stages where delicate differentiation 

 of habitats exists. Remnants indicate that the original vegetation 

 of the level summit of Smiley Heights was Adenostoma chaparral. 



Three successional stages were revealed by study of the dry 

 washes of Mill and Santa Ana Creeks, at the southern base of the 

 San Bernardino Mountains, and of other similar localities. The 

 plants upon the areas which had most recently been water-swept 

 were Baccharis viminea, Salix argophylla, S. lasiolepis, and Populus 

 fremoniii, suggesting the inception of a stream-bank community, 

 which can survive only as long as the stream holds its course. The 

 second group, a few individuals of which enter with the first, are 

 the coastal sagebrush species. The pioneer of this stage is the almost 

 leafless composite Lepidospartum squamatum. Others gradually 

 arrive, until a typical half-shrub community is established. Most 

 important on these washes are the following: 



Syrmatium glabrum. Ramona stachyoides. Opuntia covillei. 

 Eriogonum fasciculatum. polystachya. bernardina. 



Artemisia californica. Malacothamnus fasciculatus Yucca mohavensis. 



Ericameria pinifolia. splendidus. Encelia farinosa. 



Senecio douglasii. 



The last is confined to the region from San Bernardino to Elsinore, 

 so far as southern California west of the deserts is concerned, and 

 Opuntia covillei is replaced by 0. occidentalis farther west; otherwise 

 the list is representative of the whole. Selaginella bigelovii covers 

 large areas of cobbles and sand with dense growth. The third and 

 final stage comes with the establishment of Adenostoma. In the 

 younger areas we find it scattered, with many of the above list mingled 

 with it. On the areas longer undisturbed, as well as on the higher 

 terraces nearby, it forms an almost pure growth. Frequently an 

 uneroded island is seen, surrounded by bare water-swept cobbles. 

 Such an area is likely to possess a remnant of pure Adenostoma. 



In central California, washes, fans, and terraces are not such 

 striking topographic features, perhaps because the mountain fronts 

 are less abrupt and torrential erosion is therefore less powerful. 

 Still, they do occur, and the same developmental stages and the same 

 Adenostoma climax are present, though the successional species 

 are somewhat different. 



Development on coastal dunes. — A comprehensive study of the 

 strand vegetation of the Pacific Coast is now in progress. A very 



