Saltmarsh

Seen from above, saltmarshes are wonderful mosaics of land and water - green swards punctuated by sinuous creeks and isolated pans (pools). The pans are sometimes connected by an underground drainage network, and it is occasionally possible to view one of the 'pipes' in a dry pan. Saltmarshes tend to develop in quiet conditions where fine sediments are deposited by the sea but some may have been created by the drowning of coarser terrestrial sediments; there is evidence that some saltmarshes in the Western Isles were formerly machair. Many saltmarshes are associated with bays in firths or in estuaries, while smaller ones tend to occur at the head of sea lochs, and some develop on the landward side of spits and islands. Saltmarsh is often identified by the term fideach in Gaelic place-names in the north-west, and in south-west Scotland, extensive tidal saltmarsh is known as 'merse'. Saltmarsh occurs on most Scottish coasts - much the largest areas are in the Solway Firth. Scottish saltmarshes are currently more poorly known than those in other parts of the UK, and estimates of their area range from 6,000 to 7,000ha. A survey of Great Britain's saltmarshes allocated 13.7% of the GB resource to Scotland.

What are saltmarshes?

Saltmarshes are most easily defined as vegetation dominated by higher plants which is regularly inundated by salt water. Most saltmarsh vegetation is intertidal, but in some exposed situations, even on cliff-tops high above the tidal limit, there may be so much sea spray that the vegetation is identical to that on a saltmarsh.

Scottish saltmarshes are different

The vegetation of Scottish saltmarshes is very different (in general terms) from English ones. Many of the familiar English species are either confined to the south-west or absent altogether. Another Scottish feature is that the lower 'pioneer' saltmarsh that grades into mudflats is scarcer, and many Scottish systems have an abrupt seaward margin that gives way directly to mudflats. Scottish saltmarshes make good their deficiency of southern species with a range of northern elements, including saltmarsh flat-sedge Blysmus rufus and slender spike-rush Eleocharis uniglumis. The rare Eleocharis parvula has recently been discovered in the Cromarty Firth. A short, closely grazed turf containing the turf fucoid Fucus cottonnii, a tiny seaweed, is characteristic of saltmarshes in NW Scotland. In England, saltmarshes have been significantly affected by the spread of cord grass Spartina anglica, converting large areas (16.4% of the area of the habitat) to species-poor vegetation and allegedly (opinions vary) reducing the feeding area available to birds, though in some areas of England it is dying back for unknown reasons. In Wales, the coverage is even higher, at 24.9% of the habitat. It occurs on only a few Scottish sites, covering a total area of just over 100ha, or 1.67% of the area of the habitat. Its growth in Scotland is rarely extensive, except on a few sites in the Solway.

A sensitive habitat

Because they are associated with particularly sheltered situations, saltmarshes are not particularly dynamic. The tracks of a single vehicle may persist for decades as a result of soil compaction. Large areas were claimed for agriculture in the past, notably in the Firth of Forth, and these are now bounded by embankments.