244 CLIMAX AND SERE 



acterized by subordinate groupings of dominants. These minor units 

 are termed lociations, and as the name indicates are relatively local in 

 extent, occupying a few thousand square miles. They have been 

 studied chiefly in the grassland, and their biotic composition is almost 

 untouched as yet. 



In the sea, all the essential relations described above for the mixed 

 prairie are evident in communities of the sea bottom about Denmark 

 (see Chapter 7) and in Puget Sound. Weese (in Shelford et al., 1935) 

 described a series of faciations in the bivalve-annelid community of a 

 narrow bay. Faciations also occur in the large gastropod-echinoderm 

 communities in the same region. Marine lociations are best illustrated 

 in the Balanus-Littorina biome of the Pacific Coast of North America, 

 where Rice (1930) and Towlcr (1930) have described many peculiar 

 local variations in the arrangement of barnacle dominants. These are 

 explained by Rice (in Shelford et al., 1935) as caused by the com- 

 bination of low tides and warm sunny weather during the seeding and 

 early stages of the barnacles. She points out that the arrangement of 

 the dominant species is controlled by mortality, etc., during accidental 

 combinations of conditions, a fact that leaves the arrangement of 

 adults and nearly grown individuals without meaning unless the series 

 of past events is fully known. 



Among plants, a concrete community, the consociation, stands by 

 itself as a climax unit consisting of a single dominant. In associations 

 with several dominants, such as grassland and deciduous forest, con- 

 sociations reach expression regularly only in limited areas that are 

 especially favorable to each. However, when the major dominants 

 are but two or three in a particular association, one of these may form 

 an almost pure community over a large area. This is true of Pinus 

 ponderosa and of Picea engclmanni in the Rocky Mountains, of 

 Pseudotsuga mucronata on the Pacific Coast, of Artemisia tridentata 

 in the Great Basin, and of Larrea tridentata in the deserts of the 

 Southwest. In the bunch-grass prairie of California, a similar role 

 was played by Stipa pulchra up to the later historical period, and still 

 more recently by Agropyrum spicatuni in the Northwest. 



Some subspecies of animals, chiefly subinfluents, find their range 

 wholly or largely in such consociations, and the number of these will 

 probably be increased. Finally, in view of the fact that any major 

 dominant may recur more or less pure in repeated local examples, it 

 has proved convenient to refer to it as a consociation, even though it 

 is part of a particular faciation; that is, the association is divided into 

 faciations, in which the consociation appears only as local expressions. 

 The dense communities of the bivalve, Spisida siibtruncata, in the 



