PLANTS IN ARCTIC-ALPINE ENVIRONMENT — SHETLER 489 



as North America is concerned, are the works of Polunin, Porsild, and 

 Raup. I should like, however, to make a few smimiary comments 

 about plant communities. 



If we take only an oA^erview of the Tundra, we find that its plant 

 communities can be grouped in three major groups: (1) rock desert 

 communities, (2) heath and grass-sedge communities, and (3) aquatic 

 communities. 



Under rock desert communities, I include barrens, screes, rubble 

 slopes, boulder fields, pavements, and river or coastal strands and 

 dunes — any conmmunity where the vegetation is discontinuous and 

 sparsely scattered in patches or polsters (pis. 1, fig. 2; 2; 4, fig. 2; 8, 

 fig. 1 ; 10, fig. 1) . In winter, these habitats are covered by little if any 

 snow. Rock deserts may be veritable flower gardens during the short 

 flowering season (pi. 10, fig. 1), and some of the Arctic- Alpine's most 

 attractive members thrive here amidst the rocks (pi. 9 ) . Rock crevices 

 shelter a variety of species at the higher elevations, including several 

 species of ferns (pi. 11). The rocks on these rock deserts may look 

 completely barren from a distance, but all is not desert between the 

 patches of ferns and flowering plants. Lichens, especially crustose 

 lichens, cover large areas of rock surface, sometimes almost completely 

 (pi. 11, fig. 1). 



Within the continuous- vegetation group of communities, the heaths 

 and grass-sedge prairies, individual types and subtypes are almost 

 legion, and all generalizations must be treated cautiously. Mosses 

 and lichens are ubiquitous in the Arctic, forming an almost continuous 

 heath over vast areas, often as an understory to other vegetation. The 

 creamy white Cetraria cucullata (Bell.) Ach. (pi. 11, fig. 2) is a very 

 common heath lichen of the Tundra, and certain of these cetrarias 

 {Cetraria spp.) and some cladonias {Cladonia spp.) are called "rein- 

 deer moss" by some, alluding to their food role for caribou and rein- 

 deer. Dwarf-shrub heaths cover enormous areas in total, and they 

 are often dominated by species of the heather family, Ericaceae. 

 Good examples are the arctic blueberry (pi. 8) and Labrador tea 

 (pi. 12), both very widespread constituents of tundra heaths in the 

 Arctic. These heaths are very like bog heaths of temperate latitudes, 

 which probably are but glacial relicts of a once more widespread 

 arctic type of vegetation. Some of the same species, such as bog rose- 

 mary {Andromeda polifolia L., pi. 12), are found both in tundra 

 heaths and temperate bog heaths. 



The prairie communities vary from marsh or wet meadow to very 

 dry upland meadow, depending on the general terrain and microrelief . 

 In localized spots, snowflush and alder-willow thicket communities, 

 mentioned before, occur. Usually, grasses and sedges of one or more 

 species predominate in the prairie communities, but from place to 

 place large patches of herbmat will be in evidence, particularly in snow- 



