152 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA. 



destruction of {the association over wide stretches and the fact that the 

 societies have not been made the subject of definite study throughout the 

 season render the following lists more or less provisional. It has been espe- 

 cially difficult to determine the subdominants of the Stipa communities in 

 California, as the fragmentary areas are almost completely overrun with 

 annuals. The societies of such grassland areas at present are essentially the 

 same as for the chaparral (p. 193). The following list for the Agropyrum- 

 Festuca community of Washington and Idaho has been contributed by Dr. 



J. E. Weaver: 



Societies of the Agropyrum-Festuca community. 



Prevernal Societies: 

 Carex geyeri. 



Erythronium grandiflorum. 

 Claytonia linearis. 



Vernal Societies: 



Lupinus wyethii. 

 Balsamorhiza sagittata. 

 Leptotaenia multifida. 

 Phlox speciosa. 



Estival Societies: 



Wyethia amplexicaulis. 

 Geranium viscosissimum. 

 Astragalus arrectus. 

 Astragalus collinus. 

 Astragalus spaldingii. 

 Castilleia lutescens. 

 Helianthella douglasii. 

 Lupinus leucophyllus. 

 Lupinus ornatus. 



Estival Societies — continued. 

 Lupinus sericeus. 

 Gaillardia aristata. 

 Achillea millefolium. 

 Galium boreale. 

 Arnica fulgens. 



Serotinal Societies: 



Hoorebekia racemosa. 

 Solidago missouriensis. 

 Solidago serotina. 



Prevernal Clans: 

 Viola adunca. 

 Ranunculus glaberrimus. 

 Fritillaria pudica. 

 Sisyrinchium grandiflorum. 



Vernal Clans: 



Synthyris rubra. 

 Collinsia parviflora. 



Estival Clans: 



Carduus foliosus. 

 Carduus palousensis. 

 Potentilla convallaria. 

 Potentilla blaschkeana. 

 Sidalcea oregana. 

 Penstemon confertus. 

 Agoseris heterophylla. 

 Agoseris grandiflora. 

 Eriophyllum lanatum. 



Serotinal Clans: 



Hieracium scouleri. 

 Aster fremontii. 

 Aster levis geyeri. 

 Erigeron corymbosus. 

 Carum gardneri. 

 Gentiana oregana. 



THE SAGEBRUSH CLIMAX. 



ATRIPLEX-ARTEMISIA FORMATION 



Nature. — The sagebrush climax owes its character to the dominance of 

 low shrubs or bushes, of which Artemisia tridentata is the most important. 

 It is essentially a scrub desert, in which the dominants seem to have acquired 

 their distinctive vegetation-form as a rather recent adaptation to the arid 

 climate itself. In other words, they are shrubby adaptations of herbaceous 

 families, and not dwarf forms of shrubs or trees, as is true of chaparral and 

 mesquite. The formation is regarded as composed of 17 dominants, of which 

 11 belong to the Asteraceae, 4 to the Chenopodiaceae, 1 to the Polygonaceae, 

 and 1 to the Lamiaceae. These families agree in showing a high systematic 

 development, and doubtless the dominants owe some part of their success to 

 the highly specialized one-seeded fruit typical of all of them. Their success 

 is due even more largely to the acquisition of the woody habit in some degree 

 at least, and especially to the accompanying ability to sprout more or less 

 readily from the base. As a consequence, the sagebrush dominants are not 

 only well adapted to their habitat, but they are also particularly well fitted 

 to invade other habitats, wherever fire or other disturbance has weakened the 

 hold of the occupants. The result has been a widespread extension of sage- 

 brush into all of the contiguous formations, the grassland, desert scrub, 

 chaparral, and woodland, and even into the pine consociation of the montane 

 forest. These transitions are often very broad, and hence the actual delimita- 

 tion of the formation on the map is a matter of peculiar difficulty. They also 



