Fens are wetland habitats which form on peaty substrates, and which are fed by moving water from rivers and streams (as opposed to true bogs, which are largely rainwater-fed). In the lowlands, most fens are nutrient-rich, being fed by calcareous water, and support a diverse assemblage of tall, herbaceous vegetation. However, fens may also be nutrient-poor, in which case they may support Sphagnum mosses and other species associated with bogs, as at Hothfield Common. Key species associated with fen habitat include water vole, water shrew and reed bunting.
The Kent Habitat Survey notes less than 70 ha of fen in the county, with extensive areas only by the Stour at Stodmarsh, on the North Stream at Ham, and next to the Medway at Yalding. Other areas are smaller and more scattered, including small patches of fen associated with springs and small streams rising at the foot of the North Downs, for example at Harrietsham, Charing, and Holy Well, Folkestone. There are also small areas of fen associated with the North Kent Marshes.
Nutrient-poor, acid fen is now so rare in Kent, that it probably warrants action as a habitat in its own right. However, for the purposes of conservation, calcareous fen may be best considered as an important part of a complex of habitats (including standing open water, reedbed, wet grassland and wet woodland) associated with river systems and floodplains.
Almost all the existing fen habitat in Kent is protected as SSSI or SNCI, and is therefore protected from direct loss or damage. However, a number of key factors are still likely to have a negative impact on the county's remaining fen:
- Extreme fragmentation of the habitat, due to past land-drainage and agricultural intensification, and as a result of disconnection of rivers from their natural floodplains by past flood-defence works.
- Increased water abstraction, resulting in reduced spring flows. The Water Management Unit which supplies fens at Harrietsham, Charing, and most notably at Hothfield, is considered 'over-abstracted' by the Environment Agency.
- Lack of appropriate management, leading to drying, scrub encroachment and succession to woodland.
- The most important blocks of fen, in the Stour valley east of Canterbury and at Ham Fen, are protected as SSSI. Some 68% of Kent's fen habitat is within SSSIs.
- Key blocks of fen habitat at Stodmarsh National Nature Reserve and Kent Wildlife Trust's Ham Fen Nature Reserve are in positive conservation management.
- Other, smaller areas of fen (representing around 23% of Kent's total) are within Local Wildlife Sites (SNCIs).
- Some fen management is supported through agri-environment schemes administered by Defra.
- Work for key species associated with fen habitats includes survey by Romney Marsh Countryside Project survey for greater water parsnip.
Maintain the current extent of all existing Lowland Fen.
Secure the appropriate conservation management of existing Lowland Fen.
Establish two new landscape-scale, freshwater wetland complexes, one in East Kent and one in West Kent, which include between them at least 35ha of fen along other wetland types.