12] VEGETATIONAL TYPES OF TEMPERATE LANDS 371 



elucidated, some of these being sufficiently widespread to demand 

 more attention. 



Notable are the characteristic types afforded by the sand-dune 

 and shingle-beach successions which occur chiefly (but in the former 

 case by no means entirely) near sea coasts. Thus sandv sea-shores 

 that are wetted by the highest tides are commonly inhabited in 

 sufficiently sheltered situations by a characteristic open community 

 of halophytic shore-plants such as Sea-rockets {Cakile spp.), Sea- 

 purslane [Arenaria {Honckenya) peploides agg.), and species of Orache 

 (Atriplex). These tend to arrest any dry sand that is blown on to 

 them, and, consequently, to form the basis of hillocks through which 

 the shoots grow, the effect being cumulative in that the deeper 

 the sand comes to be piled up, the higher the plants will grow, 

 and vice versa. More important in this connection are the major 

 dune-formers — coarse Grasses such as, particularly. Marram Grass 

 {Ammophila arenaria) and Lyme-grass {EJymus arenarius s.l.) in north- 

 temperate regions. These have similar powers of colonization and 

 sand-accumulation but grow chiefly farther back from the sea and 

 more extensively, binding the sand by the ramifications of their 

 rhizomes and roots. This is illustrated in Fig. 93, which shows 

 Marram Grass doing the binding on the coast of Maine. Meanwhile 

 the motion of the surface particles is checked by the tall and usually 

 tufted aerial parts, and other species, which cannot colonize moving 

 sand, are enabled to establish themselves between the axes of the 

 main pioneers. These secondary colonists typically include Lichens, 

 Mosses, and less coarse Grasses, which finally bind the surface and 

 consolidate the community. Maritime shrubs and in time climax 

 forest typically follow if the land is not severely pastured or turned 

 into golf links (for which old, grass-covered dunes are the traditional 

 sites). ]\Ieanwhile there will have been produced some characteristic, 

 though serai, vegetational types whose non-halophytic counterparts 

 may occur far inland, as for example around the Great Lakes of 

 North America. 



Shingle-beach vegetation has considerable affinity with that of 

 dunes, especiallv when sand is admixed and the habitats are thereby 

 rendered similar. Where sand is lacking, various Lichens may 

 colonize the surface of the stones inland of the usual ' storm-crest ', 

 and over them may extend clumps of such maritime flowering plants 

 as the Sea-pea {Lathyriis maritimus agg.) and halophytic Grasses. 

 These often persist for a long time, the plants being rooted in the 

 crevices between the pebbles, lltimately the crevices become filled 



