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Coastal saltmarshes comprise the upper, vegetated portions of intertidal mudflats.
Saltmarshes are usually restricted to comparatively sheltered locations in estuaries,
saline lagoons, behind barrier islands, at the heads of sea lochs and on beach plains.
The development of saltmarsh is dependent on the presence of intertidal mudflats.
Saltmarsh vegetation consists of a limited number of salt-tolerant plants adapted to
regular immersion by the tides. At the lowest level pioneer plants can withstand up to
600 tides per year whereas upper marsh plants can only tolerate a few tides per year.
Saltmarsh communities are affected by many factors such as climatic differences from
west to east, sediment types, decreasing salinities and land management, especially
grazing. For example, on traditionally grazed sites, saltmarsh vegetation is shorter
and dominated by grasses. Saltmarshes on the west coast tend to differ in species and
community composition from those on the east coast.
Grazing by domestic stock is traditional for many saltmarshes, creating a sward
attractive to wintering and passage waterfowl. Less intensive grazing is better for
breeding waders in summer.
Saltmarshes are a very important resource for wading birds and wildfowl. Acting as
high tide refuges for waterfowl, breeding sites for terns, gulls and waders and a source
of food for passerine birds in autumn and winter. In winter, large flocks of geese and
ducks rely on saltmarshes.
A 1989 survey estimated the total extent of saltmarsh at 45,500 ha. England has
approximately 32,500 ha, Scotland 6,747 ha, Wales 6,089 ha and Northern Ireland
215 ha. This resource is mainly found in the major estuaries of north-west England
and in Wales. It is estimated that at the mean high water line, 24% of the English
coastline, 11% of the Welsh coastline and 3% of the Scottish coastline consists of
In North Merseyside, most coastal saltmarsh is found on the Ribble Estuary to the
north of Southport, between Southport and Ainsdale, and on the Mersey Estuary at
Oglet, Liverpool. Small areas also exist on the Alt Estuary at Hightown and in the
Very large areas of the saltmarsh in each estuary have been reclaimed for other land
uses including agriculture, industry, and development. No areas of saltmarsh in North
Merseyside are now subject to grazing by livestock, but the Birkdale Green Beach is
grazed by Rabbits.
The original extent of saltmarsh in Merseyside has been considerably reduced by land
claim. NVC surveys of the Ribble & Alt (2003) and the Sefton Coast (2004)
identified 447ha of land with a primary classification of Saltmarsh within the area
corresponding to the North Merseyside LBAP as supplied by Natural England in
2007. If the area is limited to the LA boundaries (principally Sefton) then the area is
reduced to 348ha. The extent of the Liverpool section of the Mersey Estuary is
unknown but judging from aerial photographs taken in 2005, is likely to be in the
region of 20-30ha.
In addition there is estimated to be some 138ha of coastal grazing marsh at Marshside
in Sefton. Coastal and Floodplain Grazing Marsh is a UK Priority Habitat for which
North Merseyside does not, at the time of writing (2008), have a separate HAP and
will therefore be considered within this HAP.