12] VEGETATIONAL TYPES OF TEMPERATE LANDS 373 



fens, bogs, mires, moors, and waterside zones that commonly 

 represent part of some hydrosere or other. As such, many have 

 been covered above, at least by general implication ; in other 

 instances they seem to form subclimaxes, for example of plagioclimax 

 nature where a continuing ' master factor ' is involved, and, at least 

 when covering considerable areas, appear needful of some treatment. 

 Outstanding are the marshlands, fenlands, and boglands which may 

 be distinguished respectively according to whether the soil is formed 

 mainly of silt, of peat containing considerable quantities of lime 

 or other bases, or of peat very poor in such bases. With marshlands 

 of one sort or another we are already fairly familiar, while further 

 examples are mentioned in the following chapters. 



Fenland occupies the alluvial borders of rivers and streams as 

 well as parts of old estuaries and the borders of certain lakes — 

 especially of those into which streams bring ' hard ' water rich in 

 lime. Its most characteristic manifestations represent stages in the 

 hydrosere — particularly reed-swamp, sedge-meadow, and, if the 

 latter is not regularly cut or pastured, damp scrub or woodland 

 ' carr ' dominated by Alders or sometimes Birches, or constituting 

 meadow-moors in exposed situations. The vegetation in these 

 cases is largely calcicolous, whereas in the general run of alluvial 

 marshlands it is less exacting. 



Bogs or ' mosses ', on the other hand, develop chiefly where the 

 water is very poor in calcium and other basic salts, and support 

 entirely different communities — for example around the shores of 

 lakes and tarns in areas where the rock is deficient in basic mineral 

 salts and the water is consequently ' soft '. Typically the growth 

 consists largely of Bog-mosses {Sphagnum spp.) supporting a number 

 of characteristic higher plants such as Cotton-grasses [Eriophorum 

 spp.) and Sedges {Carex spp.), and often ' insectivorous ' associates 

 such as Butterworts {Pingnicula spp.), Sundews {Drosera spp.), and 

 Bladderworts {Utriailaria spp.). In areas of cool and wet climate 

 where the drainage is poor, such communities may cover considerable 

 flattish tracts and be known as ' blanket bogs '. Owing to the Bog- 

 mosses' remarkable power of holding water in their sponge-like 

 cushions {see p. 51), these last can grow in height and enormously 

 in width, extending over marshes and even fens or open water, 

 depositing peat and raising the surface on which they grow. Such 

 ' raised bogs ' tend to be strongly acidic in reaction and reddish- 

 brown in colour. 



Although bogs are commonly colonized by Heaths or even larger 



