Water world

An ambitious project to bring back the lost fens of Cambridgeshire is now under way. Peter Marren reports on a tug-of-war between farming and conservation

Adventurers Fen, named after the merchant adventurers of old, who began the great drainage of the Cambridge-shire Fens, has a strange, tide-turning history. One hundred years ago, it was acquired by the National Trust, supposedly in perpetuity, as a nature reserve. Its marshy glories were recalled in a book by the bird artist, Eric Ennion. Then, in the 1940s, Adventurers Fen was requisitioned under the wartime "Dig for Victory" food production campaign. In a way, the digging up of this deepest of fens, this natural hollow in the flattest, lowest corner of England, was as great and surprising achievement as its conservation. The man who did it, farmer Alan Bloom, also wrote a book. In it, he described with pride how the fenny watercourses were transformed into deep trenches, the bog oaks preserved in the peat blown to pieces by dynamite, the drying reeds set ablaze.

Adventurers Fen's pair of books make a parable of the perpetual tug between exploitation and conservation, between use and delight, which has shaped the landscape of today. Which Adventurers Fen serves Britain best, the one of bitterns or the one of potatoes? The traditional answer, in the Fens must be potatoes. The Fens of Cambridgeshire must be among the most artificial non-urban landscapes on the planet. Even great cities contain green spaces that preserve the land as it was before houses were built. London has its wild parks and commons, Bristol the gorge of the Avon, Edinburgh its mountain heart at Arthur's Seat. But the Fens have been wiped clean by drainage engineers. The old riverscape of floodlands and slow, winding streams has been turned into a grid of lodes and drains scoring through a flat prairie. The few patches of wild that survived as washland are often described as "islands", when they are the opposite: patches of wet in a boundless level of dry. Only the names survive: Soham and Whittlesey Meres, the natural lakes long ago drained away, or Bottisham, Swaffham and Burwell Fens.

The rainwater and streams that kept the Fens wet are now conveyed to the sea by the steep-sided lodes and the high banked main rivers. The blanket of peat that once covered the bottomlands between Cambridge, Ely and Huntingdon has been stripped or recycled back into the fertile soils of the modern Fens. The old Fens have gone forever. Or have they? A recent feasibility study commissioned by the National Trust has concluded that much of the Fen between Cambridge and Wicken could be reflooded. In the Netherlands, large tracts of former intensively cultivated arable land has been returned to fen. The secret lies in the same process that created the farms – water control. Banks and lodes can be used to keep the water in, as well as out. A system of banks and dams could even allow farms and fen to exist side by side.

The conservationists who look after the last natural remnants of fen are worried. The nature reserves at Wicken and Woodwalton Fen have a sorry record of losses since they were set up, nearly a century ago.Woodwalton has lost its colony of Large Copper butterflies. Wicken Fen has lost another gorgeous butterfly, the Swallowtail, among many less celebrated species.

The problem is that these isolated remnants are in danger of drying out. Woodwalton Fen is surrounded by an enormous moat. It has to be: the Fen, though shrunk, is still higher than its surroundings. As fens dry out, scrub invades, smothering out the sedgebeds and marshy meadows. Fortunately, recent tinkering with banks and drains has sealed in the wet more effectively than in the past, but a fundamental problem remains. These core areas of wild are too small to offer a secure refuge, and their isolation means that when a species has gone, it has gone for ever. In the long-term, these places are not up to the job.

Adventurers Fen was handed back to the National Trust when the wartime emergency was over. A large hole was dug in the potato fields. As it flooded, the hole began to attract birdlife, but by any botanical description it wasn't a fen at all. Since then, the Trust has built up its holding there, most recently with the purchase of nearby Burwell Fen Farm in October 2001. Buying fen farms is an expensive business but with the help of donors like the Heritage Lottery Fund, this may be only the start of an ambitious project to bring back the lost fens.

The Trust ultimately hopes to restore 3,000 hectares of fen, linking Wicken Fen with the city of Cambridge, so rebuilding a natural landscape last seen in the early 19th century.The RSPB recently signed a deal with an aggregates company to convert up to 700 hectares of worked-out gravel pits by the River Ouse to reedbeds. Their immediate target is to increase Britain's bittern population from 20 pairs to a more sustainable 60 pairs. Bitterns live in reedbeds, where they feed on fish in the waterways between the marshes. They are a useful market leader, because what benefits them will also help bearded tits, marsh harriers, otters, and may be even swallowtails.

There is more to fens than reedbeds. The reed is one fen plant among at least 300, and reedbeds just one in 68 plant communities found in fenland. Natural fen is varied, with dry zones of scrub and woodland, open summer-dry grassland and beads of saw-sedge and tussock-sedge as well as reed. Much of this variety depended on low-intensity grazing. The Fens used to support a local economy based on cattle, hay cropped by the marshmen, peat cut for fuel and reeds harvested by thatchers. The new Fens will need animals. There is talk of introducing water buffalo, as part of an interesting menagerie of "conservation animals".

It is an intoxicating vision, this return of the fen. The fact of its serious consideration marks a turning of the tide, from food production to amenity and environment.