South East England Biodiversity Forum

Fens

What is it?

Fens are peatlands that receive water and nutrients from the soil, rock and groundwater, as well as from rainfall.

Fens can be described as ‘poor-fens’ or ‘rich-fens’.

Poor-fens, where the water is derived from base-poor rock such as sandstones and granites, occur mainly in the uplands or are associated with lowland heaths. They are characterised by short vegetation with a high proportion of bog mosses Sphagnumspp. and acid water (pH5 or less).

Rich-fens are fed by mineral-enriched calcareous waters (pH5 or more) and are mainly confined to the lowlands and where there are localised occurrences of base-rich rocks such as limestone in the uplands.

Lowland fens occur on soils that are at least periodically waterlogged. They range from small to extensive, but are generally circumscribed and limited in extent by agricultural or forestry activity. The category encompasses a range of water supply mechanisms. Variety also arises from differences in the constituents of the water, fluctuation levels and movement.

Fen habitats support a diversity of plant and animal communities. Some can contain up to 550 species of higher plants – a third of our native plant species. They host up to, and occasionally more than, half the UK’s species of dragonflies, several thousand other insect species, as well as being an important habitat for a range of aquatic beetles. In intensively farmed lowland areas, fens occur less frequently, are smaller in size and more isolated than in other parts of the UK.

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

The situation in the South East

 

Extent in England  8,000 ha
Extent in the SE region  1,629 ha
Percentage UK resource in the SE   20%
Extent covered by SSSI designation   

 

Rate of Change

 

 County 1998 extent (ha)  2008 extent (ha) 
 Berkshire  Unknown  108
 Buckinghamshire  Unknown  69
Hampshire Unknown
  285
 Isle of Wight 20  12
 Kent 5
 48
 Oxfordshire  30  149
 Surrey  Unknown  50
 Sussex  Unknown  908
 Total  Unknown  1629
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

Fens are dynamic semi-natural systems and, in general, management is needed to maintain open-fen communities and their associated species richness. Without appropriate management (eg. mowing, grazing, burning, peat cutting, scrub clearance), natural succession will lead to scrub and woodland forming. Current factors affecting this habitat type are:

  • Abstraction. Past loss of area by drainage and conversion to intensive agriculture. Excessive water abstraction from aquifers has dried up or reduced spring line flows and generally lowered water tables. Abstractions have also affected the natural balance between the differing water qualities of ground water and surface water
  • Small total area of habitat and critically small population sizes of several key species dependent on the habitat
  • Lack of or inappropriate management of existing fens, leading to drying, scrub encroachment and succession to woodland
  • Valley fens are particularly susceptible to agricultural run-off and afforestation within the catchment
  • Enrichment or hyper-trophication resulting in changing plant communities

Vision for Lowland Fen

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

  • No further loss of existing habitat
  • Good management including, where appropriate, scrub control, light grazing and visitor management
  • No damage to site integrity from activities arising outside the sites, eg. inadequately managed public access • Re-creation of lowland fen on appropriate sites to restore some past losses, including the linking up of fragmented sites
  • Greater public appreciation of lowland fen and their specialist wildlife, including greater awareness of the impacts of human pressures

How we can deliver this vision