CLIMAX COMMUNITIES: PRESENT DISTRIBUTION 239 



exposures eventually results in a lichen-moss mat, which may con- 

 tinue almost indefinitely. 



Important climax dominants are Cassiope tetragona, one or more 

 species of Vaccinium, Arctostaphylos alpina, Empetrum nigrum, 

 Andromeda polifolia, Ledum palustre, Rhododendron lapponicum, 

 and species of Betula and Salix. These and other species occur in 

 varying combinations and degrees of importance. 



Practically all habitats support some of the many species of 

 Carex, of which the commonest include Carex capillaris, C. nar- 

 dina, and C. rupestris. The preclimax sedge community invariably 

 includes Elyna bellardii in abundance. Some grow in mats, some 

 are in clumps, but all are dwarfed. The same can be said for the 

 grasses, which, although relatively abundant and widespread, are 

 restricted to a few genera, of which Festuca and Poa are espe- 

 cially well represented. Many of the conspicuous herbs previously 

 mentioned are included in the numerous species of one of the 

 following genera : Saxifraga, Potentilla, Ranunculus, Draba, Cer- 

 astium, Silene, Lychnis, Stellaria, Castilleja, and Pedicularis. Con- 

 spicuous and widespread species typical of tundra are Oxyria 

 digyna, Papaver spp., Dry as octopetala, and Epilobium latifolium. 



Alpine Tundra— Mountains high enough to have a timber line 

 support tundra, whose upward extent is limited by the snow line. 

 In the east, as a consequence, tundra is found only on a few high 

 peaks in New England. Farther south, the Appalachians are not 

 of sufficient height to support tundra. That on Mt. Washington 

 is representative of the type and is essentially similar to the not far 

 distant arctic vegetation. 



Alpine tundra in the western mountains mostly lies far to the 

 south of the arctic and is consequently found at high altitudes 

 only. In the Canadian mountains, it is found as low as 6,000 feet, 

 but southward its altitudes grow progressively higher. In the 

 Rocky Mountains of Colorado, it is well developed between 

 11,000 and 14,000 feet. In the Sierra Nevada, where many peaks 

 are higher, the snow line is lower, and thus, tundra lies mostly 

 between 10,500 and 13,000 feet. 



When climate changed and terminated the glacial period, vege- 

 tation similar to modern tundra must have followed the ice as it 

 receded northward. This left only these high peaks and ridges 



