South East England Biodiversity Forum

Coastal and floodplain grazing marsh

What is it?

 Grazing marsh is defined as periodically inundated pasture, or meadow with ditches that maintain the water levels, containing standing brackish or fresh water. These ditches are especially rich in plants and invertebrates. Almost all areas are grazed and some are cut for hay or silage. Sites may contain seasonal water-filled hollows and permanent ponds with emergent swamp communities, but not extensive areas of tall fen species like reeds; although they may abut with fen and reed swamp communities.

Please see the UK BAP website or the regional BAP habitat definition or the UK BAP habitat definition for more information.

The situation in the South East  

 

Extent in England  app. 200,000 ha
Extent in the SE region

 28,300 ha

Percentage UK resource in the SE   14%
Extent covered by SSSI designation  app. 15% - 20%

 

The vast majority of grazing marsh in the South East is comprised of improved grassland of low nature conservation interest. The conservation interest is greater on land that is not drained or otherwise agriculturally improved.

Grazing marshes are particularly important for a number of breeding waders such as snipe (Gallinago gallinago), lapwing (Vanellus vanellus) and redshank (Tringa totanus), and for the wintering wildfowl they support. Some coastal grazing marshes in the South East support internationally important populations of wintering Brent geese (Branta bernicla bernicla).

Grazing marshes may have a characteristic sward rich in flowering plants, including cut grass (Leersia oryzoides) and divided sedge (Carex divisa). The ditch systems of grazing marshes support many aquatic plants and characteristic invertebrates such as rare dragonflies and water beetles. In coastal systems, there can be significant lagoonal interest in these ditches. Grazing marshes often also support mammals such as otter (Lutra lutra) and water vole (Arvicola terrestris).

Examples of important grazing marsh sites in the South East include:

  • Avon Valley, Hampshire and Dorset
  • Pevensey Levels, East Sussex
  • North Kent Marshes
  • Arun Valley, West Sussex
  • Brading Marshes, Isle of Wight
  • Upper Thames Tributaries

There are 170,000ha of coastal and floodplain grazing marsh in England, 30,000ha of which is in the South East. This forms 17% of the UK’s total resource.

Rate of Change

 County 1998 extent (ha)  2008 extent (ha) 
 Berkshire  1080 0 
 Buckinghamshire  700 0 
 Hampshire  2750  8050
 Isle of Wight  520  530
 Kent  5240  7798
 Oxfordshire  4930  355
 Surrey  50  140
 Sussex  11400  11464
 Total  26670  28345
1998 data taken from 'The Biodiversity of South East England - An Audit and Assessment' published by the Wildlife Trusts of South East England and the RSPB, South East and Central Regions  

2008 data taken from regional or national BAP habitat inventory. Please note that some of the changes listed here are due to improvements in mapping and habitat definition. 

 

Current threats

This habitat has undergone significant losses throughout the UK due to drainage and associated agricultural intensification, including conversion to arable, inappropriate ditch management and urban development. Between the 1930s and the 1980s, approximately 64% of grazing marsh was lost from the Greater Thames (72% from London and 52% from north Kent). Most of this loss was through conversion to arable land and to development.

Naturally functioning floodplains are rare in the UK, where most watercourses have been engineered and regulated. Many watercourses in the South East have been straightened, over-deepened, embanked and had water level control structures introduced in order to keep water off the floodplain. Such engineering works have served to isolate rivers from their floodplains, which has reduced the ecological value of many grassland habitats. With this protection from flooding, many developers have identified floodplains as attractive areas to build on.

Grazing marshes are dependent on an adequate supply of clean water and are further threatened by nutrient enrichment and low water tables due to groundwater abstraction; both of these threats can be exacerbated by drought.

The primary threats to grazing marsh are of both a widespread and localised type.

Widespread factors include:

  • Ecologically insensitive flood defence works constructed in the past.
  • Agricultural intensification.
  • Neglect in the form of a decline in traditional management.
  • Eutrophication

Localised effects arise from:

  • Industrialisation and urbanisation (particularly in the Greater Thames)
  • Coastal grazing marshes are at threat from climate change due to sea level rise
  • Changes in coastal flooding regimes could alter the vegetation of these marshes by converting them to saltmarsh or mudflat. There are opportunities to allow coastal grazing marsh to migrate up river valleys an into the coastal hinterland; these issues are being addressed through Shoreline Management Plans

Secondary threats include:

  • Groundwater abstraction
  • Pollution of groundwater or surface water
  • Aggregate extraction

Vision for coastal and floodplain grazing marsh

The South East Biodiversity Forum’s vision for this habitat is that there should be:

  • No further loss of existing habitat. In particular, ensuring that grazing marsh of similar quality is created to landward of flood defences that have been abandoned or breached as sea level rises. Achieved by mapping where compensatory habitat will be created in Shoreline Management Plans and other plans set out by statutory agencies
  • Good management, including where appropriate scrub control, light grazing and visitor management, on all extant sites
  • No damage to site integrity from activities arising outside the sites, eg. inadequately managed public access
  • Restore and improve relict coastal and floodplain grazing marsh (C&FPGM) habitat (eg. dry C&FPGM with inappropriate hydrological regime, agriculturally improved sites)
  • Re-establish C&FPGM of wildlife value from appropriate land sources (eg. arable land).
  • Greater public appreciation of C&FPGM and their specialist wildlife, including greater awareness of the impacts of human pressures, such as dog-walking, and dumping of waste
  • Creation of alternative green space around important C&FPGM areas under pressure for increasing new housing

 

How we can deliver this vision

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