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BIODIVERSITY REFERENCE
 
British habitats
 
   Fens   
 
(page 2)


 

ACCESS: DROVES AND WATERWAYS

As already indicated, most large fens have a past history of extensive management. Small fens or those in valley mires may be relatively natural, but a history of peat cutting or sedge harvesting requires routes of access. Water levels in the same fen systems have required control. Consequently the geographical Fenland has an ancient system of lodes, navigable waterways, some apparently dating back to Roman times. Subsidiary to these are dykes, which when clear may be able to take small boats, and additional drainage ditches. Cut routes through the fen are droves and again some are at least a few hundred years old. They provide a continuing short turf habitat and may support a flora of small sedges, rushes and herbs that cannot compete in taller vegetation.

 
Wicken Lode, an ancient, continually navigable waterway, now mainly used by holiday barges. It is bordered by the Lode Bank, a drove which itself is of substantial age. It is higher and dryer than most of the Fen droves, which are often temporarily flooded in the winter months. Wicken Fen, Cambridgeshire, May 1998.
 

The waterways are of great importance for their aquatic fauna and flora. The smaller dykes and ditches are readily colonised by submerged and floating-leaved aquatic plants, including, in rich fens, populations of local or rare stoneworts (Charophyta). The invertebrate fauna may be equally diverse. Further colonisation by taller aquatic macrophytes such as the Common Reed (Phragmites australis) is likely and the probability is that the dykes will become clogged with vegetation and silt. At length they may be crossable on foot and their value for water management, and indeed for their fauna and flora is lost. A cyclic programme of clearance maintains the waterways and ensures continuing habitat for rare species.

 
Water Violet (Hottonia palustris) amongst other aquatic macrophytes colonising a drainage dyke. Wicken Fen, May 1998.
 


 

CONSERVATION

"Open water and flood-plain mires have probably been more extensively destroyed by man in Britain than those of any other class. This is especially true of the once vast swamps and marshes of the East Anglian Fenlands, occupying the large shallow basin of the three main rivers draining to the Wash. Many others have been reclaimed for agriculture, since the richer types of fen peat give a very fertile soil when dried out, and a great many have been partly drained or modified by human activity."
(Goode & Ratcliffe, in Ratcliffe, 1977)

Ratcliffe does go on to make the point that the Norfolk Broads owe their present existence to human activity. Large scale cutting of peat in the Middle Ages formed extensive hollows that have flooded and undergone succession, now forming important habitats from open water to rich fen and carr.

Mire surfaces are often sensitive to disturbance and uncontrolled public access can cause considerable damage to vegetation and to ground nesting birds. Trampling damage can be reduced by provision of boardwalks, which also have the effect of controlling the route taken by casual visitors.

Wicken Fen, being (mostly) owned by the National Trust, is managed to allow public access, which must then be balanced against conservation necessities. A circular nature trail via boardwalks takes visitors through most of the main habitats, permits access to the windpump and bird hides and ensures minimal damage to the Fen. Effectively the boardwalk is also a bridge across much of the wetter ground and (usually) means that waterproof footwear is not necessary. Wicken Fen, July 1998.
This particular section of the boardwalk has been replaced and re-routed since the taking of this photograph.


The dramatic loss of fenland habitat has taken its inevitable toll with regard to the specialist plants and animals of such habitats. Senecio congestus, the Marsh Fleawort, was once a plant of fen ditches in the Lincolnshire and East Anglian fenlands but is long extinct. A second Senecio species, S. paludosus, the Great Fen Ragwort, was also thought long extinct until a very few plants appeared on a cleared ditchbank in Cambridgeshire in 1972, evidently from long-buried seed. The population has been maintained and plants have been transferred to a safer location, though it is reasonable to expect that the surviving British stock is genetically impoverished. Other plants such as the Fen Orchid, Liparis loeselii and the Fen Violet, Viola persicifolia are critically endangered.

Predictably there are a number of birds confined to fen habitats. The East Anglian fens are the main British stronghold of the Bearded Tit (Panurus biarmicus), a species of reed-beds. Savi's Warbler (Locustella luscinoides) is another reed-bed species that once bred in the Fenlands before becoming extinct in Britain. It has re-established itself in Britain since the 1950s, with Wicken Fen being a key site. The Marsh Harrier (Circus aeruginosus) is arguably the special bird of prey of the East Anglian fens. After coming close to extinction from use of cyclodiene agricultural pesticides, populations are now recovering following banning of these chemicals from agricultural use.


 

THE RÔLE OF THE ENTOMOLOGISTS

It was, however, the entomological interest of the East Anglian fens that first led to preservation of surviving fragments as nature reserves. The strong interest, particularly in butterflies and moths, during the 1800s meant that not only were the fens much visited, but also that sedge cutters were able to supplement their incomes by finding and selling larvae of the more sought after species. As the old Fenlands were turned so rapidly into productive agricultural land, it was the entomologists who first seem to have realised the value of holding onto and preserving some remnant of the old watery wilderness. The Swallowtail butterfly became a symbol of such efforts, though as it turned out, "preservation" of its remaining Cambridgeshire location was not enough, conservation through management was also needed and was sadly lacking in the early years of the 1900s. Other species, such as the Large Copper butterfly and the Reed Tussock moth were already extinct in Britain before any thought was given to conserving the Fens.

The Swallowtail (Papilio machaon) is now confined in Britain to the Norfolk Broads, though it was once also a classic butterfly of the geographical Fenland and persisted at Wicken Fen until the 1950s. Its distribution is necessarily limited by that of its foodplant, the Milk Parsley (Peucedanum palustre), which itself is a nationally scarce species, virtually confined to the old Fenland and the Norfolk Broads and extinct in most of the northern part of its range.

The Milk Parsley is a plant of rich fen, growing in sedge and litter fields and dependent on suitable cutting regimes. There have been several attempts to reintroduce the Swallowtail to Wicken Fen and management of the sedge and litter fields has included maintenance of its foodplant as a priority. However, past encroachment of carr has reduced the suitable area and it seems that at the present time the remaining area is too vulnerable to both drying and flooding for the Swallowtail population to remain viable. Clearance of some of the carr is a management priority, though it may be noted that a successful introduction from Norfolk will not replace the loss of genetic diversity. Dempster et al. (cited by Heath et al., 1984) carried out a museum study that suggested that Wicken butterflies were genetically somewhat different from those of Norfolk, a not unlikely result of the fragmentation of the old Fenland habitat.

It should also be noted that there are early records of the Swallowtail in Britain that suggest a much wider distribution in southern England and perhaps use of a broader spectrum of foodplants such as the relatively common Wild Carrot (Daucus carota) (Morris, 1870). Whereas the endemic British subspecies, Papilio machaon britannicus, is strictly a fenland butterfly feeding only on Milk Parsley, the widespread continental subspecies, Papilio machaon bigeneratus, is less restricted in its diet. It is possible these early records simply represent occasional vagrants from the continent, but it was collected in some numbers at least in Dorset. The Swallowtail had been locally abundant in the Fenlands of Huntingdonshire and Cambridgeshire but there were already concerns for its survival in the latter part of the 1800s. As the fens became the last refuge of this butterfly in Britain, perhaps isolation then further defined our endemic subspecies?
The illustration is taken from Morris (op. cit.) and was based on an 1851 Cambridgeshire specimen.


[To be added: accounts of the Large Copper & Reed Tussock. Ecotypic adaptation and genetic consequences of human disturbance in the Fen Nettle.]


 

FURTHER INFORMATION

Wicken Fen is the best documented fenland site, as well as being an area in which the author has a research interest, so has been much cited in this web profile. Much more is to be found at:

•   Wicken Fen Vision
    http://wicken.org.uk
    The official site (National Trust) of the Wicken Fen National Nature Reserve, with the management plan and plenty else on this area of ancient fenland. There was an older site, formerly at http://www.demon.co.uk/ecoln/wicken_fen/index.html (English Nature) which contained a wealth of information. Though sadly gone, it is archived at the Wayback Machine (insert the URL and wait ...).
 
•   Fungi of Wicken Fen
    http://www.lastdragon.org/wicken/wickenfungi.html   (link temporarily unavailable)
    Primarily of research and specialised interest, but gives some extra background to habitats in the Fen.
 

For a very comprehensive account of Wicken Fen, its history, management and natural history, see Friday (1997). It has much of great relevance to fens in general. A detailed account of the history and past management of Wicken Fen is also given by Rowell & Harvey (1988).

Godwin (1978) gives an excellent account of the history of Fenland, with much on past and present management and conservation. Goode & Ratcliffe (in Ratcliffe, 1977, chapter 8) give an excellent overview of British peatlands including fens, their diversity and conservation criteria. Volume 2 of the same work summarises key British fenland sites selected as grade 1 or grade 2 SSSIs. A valuable compendium of detail, if somewhat outdated now, was provided by Tansley (1939). For a modern overview of mires, with a rigorous examination of terminology, see Wheeler & Proctor (2000).


References:

  • Friday, L., (ed.) (1997). Wicken Fen: the making of a wetland nature reserve, Harley Books, Colchester.
  • Godwin, H., (1978). Fenland: its ancient past and uncertain future, Cambridge University Press, Cambridge.
  • Heath, J., Pollard, E., & Thomas, J., (1994). Atlas of butterflies in Britain and Ireland, Viking, Harmondsworth.
  • Morris, F.O., (1870). A history of British butterflies, 3rd ed., Bell and Daldy, London.
  • Ratcliffe, D.A., (ed.) (1977). A nature conservation review, vol. 1, Cambridge University Press, Cambridge.
  • Rodwell, J.S., et al., (1995). British plant communities. 4. Aquatic communities, swamps and tall-herb fens, Cambridge University Press.
  • Rowell, T.A., & Harvey, H.J., (1988). The recent history of of Wicken Fen, Cambridgeshire, England: a guide to ecological development. Journal of Ecology 76: 73-90.
  • Stewart, A., Pearman, D.A., & Preston, C.D., (1994). Scarce plants in Britain, JNCC, Peterborough.
  • Tansley, A.G., (1939). The British Islands and their vegetation, Cambridge University Press, Cambridge.
  • Wheeler, B.D., (1984) British fens - a review, in Moore, P.D., (ed), European mires, Academic Press, London.
  • Wheeler, B.D., & Proctor, M.C.F., (2000). Ecological gradients, subdivisions and terminology of north-west European mires. Journal of Ecology 88: 187-203.


Note: Like much of this site, these pages are likely to be the object of continuing development and review.


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© A.J. Silverside
e-mail: alan.silverside@uws.ac.uk
Page first hosted at www-biol.paisley.ac.uk/bioref/, April 2000; transferred to lastdragon.org with minor edits, September 2009 (update pending)
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