190 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA. 



competition of the grasses. This becomes controlling in the case of both 

 propagation and reproduction and makes clear why the spread of a particular 

 clump or the beginning of a new one depends upon the recurrence of wet 

 phases, in which the upper layer of the soil contains more water than the 

 grasses need. The size and continuity and the height of the shrubs reflect the 

 water relations with much accuracy and are in close accord with the gradual 

 decrease of rainfall to the west. This relation is naturally disturbed or 

 obscured by fires and grazing, though it is rarely hidden by them. Repeated 

 fires confine or destroy the shrubs, while grazing reduces the water require- 

 ments of the grasses and correspondingly increases the growth and spread of 

 chaparral. This is obviously not true in the case of browsing animals, such as 

 goats. 



SOCIETIES. 



The societies of the subclimax chaparral are derived wholly from the forest 

 or grassland. Practically none of these societies are peculiar to it, though some 

 of those derived from the grassland are more or less characteristic, owing to 

 their increased height or abundance in the shade. Among the important 

 woodland species are Fragaria virginiana, F. vesca, Viola cucullata, Galium 

 aparine, G. boreale, Aralia nudicaulis, Smilacina stellata, Sanicula marilandica, 

 Aster levis, Heliopsis scabra, Urtica gracilis, and Elymus virginicus. From the 

 grassland have entered Poa pratensis, Monarda fistulosa, Vicia americana, 

 Anemone canadensis, A. cylindrica, Oxalis stricta, Liihospermum hirtum, 

 Potentilla arguta, Teucrium canadense, Lepachys columnaris, Artemisia gna- 

 phalodes, Solidago canadensis, S. rigida, and others. 



THE COASTAL CHAPARRAL. 

 ADENOSTOMA-CEANOTHUS ASSOCIATION. 



Nature and extent. — The Coastal or Pacific chaparral differs from the Petran 

 in consisting chiefly of evergreen or sclerophyll dominants. One of the four 

 major dominants, Quercus dumosa, is imperfectly evergreen, and about 20 per 

 cent of the minor dominants are deciduous. This association is regularly 

 much more massive and continuous than that of the Rocky Mountains. This 

 is true, however, only of California, where the chaparral reaches its best 

 expression, and toward the north and southeast the community is similarly 

 interrupted. Apart from the fact that the one is typically deciduous and the 

 other typically evergreen, the two associations resemble each other closely 

 in the form, height, and general behavior of the dominants and the essential 

 character of the community. The Coastal association has been more subject 

 to fire and its responses to this agency are correspondingly emphasized. It is 

 also unique in passing gradually into a very similar but distinct subclimax 

 chaparral typical of the montane zone. 



The Coastal association is best developed on the Coast and cross ranges of 

 middle and southern California and in northern Lower California. Although 

 reduced in species, it is still an important community in northern California 

 and Oregon, but beyond this it is represented by a single species and is very 

 fragmentary. It extends eastward to the lower slopes of the Sierra Nevada 

 and thence to southeastern California and adjacent Nevada and Arizona. 

 Here it is reduced to Ceanothus cwieatus greggii and Arctostaphylus pungens, 



