THE ALPINE MEADOW CLIMAX. 231 



at present, if not an actual though more remote relationship. These are largely 

 in the Ufe-form, habits, and size of the dominants and in the genera of many of 

 the subdominants. A more definite relationship is seen in the presence of 

 Carex filifolia as a dominant in both, in the contact maintained by such 

 closely related species as Carex rupestris and C. obtusata, and by the important 

 part which Selaginella rupestris may take in both. A similar suggestion is 

 contained in the presence of Festuca and Agropyrumin both communities also. 

 At present the chief contact of the arctalpine climax is with the subalpine 

 forest in the Rocky Mountains and the Sierra Nevada-Cascade axis and with 

 the boreal forest in northern Canada and Alaska. The ecotone is very ir- 

 regular, and tongues and outposts of the one may extend far into the other. 

 In the mountains the two are sometimes separated by a narrow belt of scrub, 

 and this is often, if not regularly, the case in the Barren Grounds of the north. 

 The lower temperatures and higher water-content of the broader mountain 

 valleys have afforded a ready pathway for the downward movement of alpine 

 species and also perhaps for the upward migration of lowland hydrophytes. 

 In any event, the wet meadows and grasslands of the subalpine and montane 

 zones furnish a meeting-place for the more mobile species of two floras. 



Associations. The arctalpine climax has received almost no ecological 

 study outside of the central Rocky Mountains. Much attention has been 

 given to the floristic differences of various portions of it, but this has taken no 

 account of dominance and succession, which are vital to an understanding of 

 the vegetation. As a consequence, it is more than usually difficult to delimit 

 the associations and determine their relationship. This is particularly true 

 of the vast Arctic portion, owing to the inherent difficulties of travel and 

 investigation in such a region. The table of dominants on page 230 indicates 

 a close relationship between the eastern and western portion of the Arctic 

 region, and one closer than with either the Petran or Sierran. On the basis of 

 dominants the latter are less closely related to each other, and the subdomi- 

 nants confirm the view that they should be regarded as two associations. In a 

 table of the characteristic alpine species of Washington, Piper (1906: 63) has 

 indicated their occurrence in the Arctic region, in the mountains of California, 

 and in the Rocky Mountains. Of 156 species found on the high peaks of 

 Washington, 72 occur in California, 56 in the Arctic region, and 49 in the 

 Rocky Mountains. 



For the above reasons, it proves necessary to recognize a Petran and a 

 Pacific or Sierran association. The best evidence at present indicates the 

 presence of a single Arctic association from Greenland and Labrador to Alaska. 

 This is very little known, and it may prove desirable to recognize an eastern 

 and western association with fuller knowledge. It has not been seen by the 

 writer, and the general absence of ecological information in regard to it makes 

 it undesirable to touch it more than incidentally. Hence, the discussion below 

 deals only with the alpine portion of the formation and the corresponding 

 Petran and Pacific or Sierran associations. 



