Evaluation of conservation • Saltmarsh as a habitat • Geographical range of variation • Relationship with other habitats

Evaluation of conservation importance of saltmarsh habitat

The value of a saltmarsh and its evaluation for nature conservation interests has traditionally involved the identification of important vegetation types, their sequence across an individual marsh and regional variation saltmarsh types. However, in recent years there has been greater consideration of the importance of saltmarsh-estuarine sites as ecosystems and the emphasis for determining value has shifted based on the interaction between processes and the resulting habitat complex. Thus, aspects such as geomorphology and the maintenance of processes have become of critical importance in assessing and evaluating the overall value of saltmarsh habitat from a biodiversity and nature conservation perspective.

Saltmarsh as a habitat

Saltmarshes support a wide range of plants and animals, many of which are specially adapted to the rigours of an environment where they are regularly covered by the tide. Consequently, many of the species present are found nowhere else. Because of the tendency of marshes to accrete and to develop in zones roughly parallel with the shore and related tidal regime, they represent one of the few examples of so-called primary succession (see saltmarsh types). Furthermore, many of the larger estuarine saltmarshes represent some of the most extensive areas of natural and semi-natural habitat in an intensively used landscape. As such, they are important wildlife areas, because they are extensive, diverse, rare, ‘natural’ and vulnerable.

Geographical range of variation

Superimposed on the value the saltmarsh provides based on its associated plant and animal communities, is an interest which stems from the differences that characterise the geographical range and variation in the plant communities. Thus, the marshes of the south and east of England provide a link with those of the warmer south, including the Mediterranean, while those in the north which are more restricted, show affinities with those of the Arctic. The saltmarsh gradient in Britain is marked by a discontinuity between the Solway in the west and the Firth of Forth in the east. North of this line, species such as sea lavender, sea purslane and cord grass, which are dominant in the south, cease to be a major component of the vegetation.

Relationship with other habitats

The saltmarsh forms only one part in the complex sequence of habitats that make up the estuarine ecosystem. In the same way that the various components of the saltmarsh interact to support the wide range of plants and animals that live there, they are, in turn, important to the physical functioning of the whole system (see Morphology and Processes). At the same time, many saltmarshes only develop because they are sheltered from the extremes of tides and storms. Scolt Head Island in Norfolk, a barrier island characterised by shingle spits and sands dunes that enclose some of the most important examples of saltmarsh vegetation in Europe, clearly indicates the way in which one habitat is dependent on the morphology of another.

Interaction also occurs with mobile species where (at the level of an individual plant) an invertebrate species may feed on one part of the plant, rest on another and lay its eggs on yet another. At an even wider scale, wintering waterfowl tend to move between estuaries when they migrate and during the winter, and may nest in the uplands of Britain (Dunlin) or in the Arctic tundra (Knot).

There is no obvious physical link between saltmarshes in one estuary and another. However, many species travel between the marshes on individual estuaries and, for some of sea mammals and birds, between continents. The overall importance of the many links in the chain for the survival of much of the nature conservation interest of an individual estuary and its saltmarsh cannot be overemphasised. Thus, managing an individual marsh for nature conservation not only protects the plants and animals that occur there, but also contributes to the conservation of the estuarine ecosystem and, ultimately, the migrating birds which move between estuaries. Thus, whatever the individual situation on a saltmarsh, the large wheeling masses of wintering flocks of wildfowl and waders are a visual manifestation of a complex and rich environment.