Along the sheltered east coast of Walney Island four distinct areas of saltmarshes have developed - North End Marsh, Tummer Hill Marsh, Wylock Marsh, and Haws Bed Marsh. Tummer Hill Marsh is the largest area of ungrazed saltmarsh in South Cumbria, while Wylock Marsh and Haws Bed Marsh have stepped profiles - meaning that a distinct transition from an older (higher) marsh to a younger (lower) marsh can clearly be seen. On their lower sides all the marshes are flanked by sandbanks and mudbanks.
The following are just some of the plants that inhabit the local saltmarshes:
Salicornia europa or glasswort
Pioneer saltmarsh is developing at the lower reaches of the saltmarshes where the vegetation is frequently flooded by the tide. Wave exposure is particularly important in determining whether pioneer saltmarsh will colonise an area, as it is only able to do so in sheltered sites where it is protected from strong wave action. Pioneer saltmarsh is an important precursor to the development of more stable saltmarsh vegetation. Pioneer saltmarsh is dominated by glasswort Salicornia which forms a key stage in the transition from the extensive inter-tidal sand and mudflats to the distinctive saltmarsh of not only Walney's SSSI's but large areas of Morecambe Bay.
Saltmarshes play a fundamental role in the life of estuaries, bringing stability to their margins and also operating as a source of primary productivity. They are a rare and specialised habitat in their own right and many of the plants which occur there survive nowhere else. Saltmarsh develops when vegetation colonises soft inter-tidal sediments of mud and sand in areas protected from strong wave action. Saltmarshes exhibit a zonation of vegetation which is influenced by the degree of tidal inundation, in turn related to the level, or height of the deposited sediment on which the saltmarsh has developed. This zonation is generally displayed as bands of characteristic vegetation communities. The lower levels of the saltmarsh, landward of the pioneer zone of glasswort, experience the greatest number of tidal inundations and are generally species poor. In the mid marsh zone, as the number of tidal inundations decreases the vegetation becomes more diverse with a more complex structure and a greater proportion of herbs. At the upper levels of the marsh, which the tide only reaches on the highest spring tides, the vegetation is diverse and includes some species which are restricted to this zone.
Low marsh communities:
The lower levels of the saltmarsh, landward of the pioneer zone of glasswort Salicornia, experience a great number of tidal inundations, usually more than 360 a year. Because of this, the vegetation communities of the low marsh and low-mid marsh are often species poor, composed of plant species which can withstand such conditions. Characterising species of this zone include extensive areas of saltmarsh grass Puccinellia maritima with smaller areas of sea purslane Halimione portulacoides in ungrazed areas.
Mid marsh communities:
The mid marsh zone comprises a transition between low and upper marsh. As the number of tidal inundations becomes less frequent, the vegetation becomes more diverse with a more complex structure and a greater proportion of herbs. This zone is characteristically dominated by the saltmarsh grass/fescue Puccinellia/Festuca communities, of which over 1,000 have occur in the Bay, and by smaller areas of saltmarsh rush Juncus gerardii community.
High marsh communities:
At the upper levels of the marsh, tidal inundation only occurs on the highest spring tides and the vegetation reflects this with some species being restricted to this zone. The sea rush Juncus maritimus community is found in this zone and is more strongly represented in Morecambe Bay than elsewhere in England. Other important features of the higher saltmarsh communities include the saltmarsh flat-sedge Blysmus rufus and a fewflowered spike-rush Eleocharis uniglumis communities which are rare in Morecambe Bay (Burd, 1989).
Transitional high marsh communities:
The higher marsh communities will grade into transitional communities at around extreme high water spring tide. Transitional communities are an important structural aspect of the upper saltmarsh. They may be freshwater transitional communities, such as the common reedbed Phragmites australis, common-club rush Schoenoplectus tabernaemontanii and sea club rush Scirpus maritimus communities, or grassland transitions include creeping bent Agrostis stolon~fera, red fescue Festuca rubra and tall fescue Festuca arundinacea communities. Historically, where the upper saltmarshes have been truncated by sea walls, these habitats have been lost.