Key Species • British Saltmarsh Types • Spartina marsh

British Saltmarsh Types

Much of the work undertaken on saltmarsh classification has drawn a contrast between saltmarshes in the south and east and those in the north and west. Attempts to provide a broad geographical classification of British saltmarshes have also noted this distinction. Adam (1990) recognises three main groups of communities which he calls Type A, B and C.

Type A marshes are relatively low in diversity with Spartina grass or rayless sea aster commonly occurring as pioneers, sea purslane common in the mid marsh and sea couch a frequent component of the upper marsh. Type A marshes mostly occur in southeast England . Type B marshes may also have Spartina present but the pioneer and lower marsh is usually dominated by common saltmarsh grass and the mid and upper marsh by red fescue and saltmarsh rush. Type B marshes are common in northwest England and Wales . Type C marshes are characteristically species-rich, especially in the upper marsh and include many non-halophytes. Although they occur elsewhere (as do marshes of Type A and B), Type C marshes are most abundant on the west coast of Scotland .

There are other important general differences between marshes in the west and those in the south and east. The most important may be the recent history of grazing, most west coast marshes having been extensively grazed for many decades, but variation in substrate is also a confounding factor. West coast saltmarshes occur mainly on sandy substrates whereas those on the east and south coasts are predominantly on fine silts and clays. There are climatic differences too, with higher rainfall and less extreme temperatures in the west.

It is also possible to recognise geographical variation in the British saltmarsh flora, variation which reinforces the contrast between Scottish, west coast and south east saltmarsh types. One group of species does not occur further north than a line between the Solway and the Firth of Forth. It includes sea purslane, sea couchgrass, sea hard-grass and both common and lax-flowered sea lavender (Limonium humile). A second group, restricted to saltmarshes below a line from The Wash to South Wales, includes species from the upper marsh such as sea heath and shrubby sea blight whose main centre of distribution is the Mediterranean, as well as low and mid marsh species such as cord-grass, perennial glasswort and golden samphire (Inula crithmoides).

The combination of all of these factors, floristic elements, substrate, climate and history of management, especially stock grazing, makes it difficult to be dogmatic about a 'natural' classification of British saltmarshes. Whilst bearing in mind the broad northwest/southeast distinction, it is important to note that there is a good deal of local variation and that, perhaps contrary to popular belief, saltmarshes are far from uniform in nature.