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Wetland

Wetlands form over any land whose soil is either seasonally or permanently waterlogged. This can happen alongside rivers, across floodplains, where there are springs and seepages, a high water table or tidal incursion.

Waterlogging tends to exclude oxygen from the soil and plants have evolved many ways to deal with this, leading to the evolution of hundreds of specialist wetland and waterside species.

Wetland habitats include marshes, fens, bogs, water-meadows and any muddy place by water; they are found all across the UK and often include systems of aquatic habitats such as ditches, rills and streams which can also be important for plants. Wetland complexes such as the Broads, Somerset and Pevensey Levels, form extensive networks of habitats which are rich in many other forms of wildlife.

Habitat features

Bogs

Upland and Lowland bogs are characterised by the dominance of Sphagnum moss species, which lay down layers of bog peat as they grow. Sphagnum acidifies its own environs and so bog systems are populated with plants that can cope with base-poor, acid waters. Our upland blanket-bogs cover more than 10,000 hectares of land and are hugely significant in the landscape. Lowland bogs are much less extensive, are more fragmented and prone to damage; our largest extent, in the Humberhead levels, has been badly damaged in recent decades as a consequence of peat removal at an industrial scale

Fens and reedbeds

This kind of habitat occurs in river valleys and floodplains that are not conducive to the development of Sphagnum dominated vegetation. Sedges and ruches tend to dominate and common reed is a prominent species, although its abundance is greatly affected by management; fens and reedbeds have a very long history of traditional management, some being grazed but many cut for ‘fen litter’ or ‘marsh-hay’, a product that went for feed and bedding for the many thousands of horses that once populated our towns and cities. Fen-litter and saw-sedge, another traditional fen product, are both cut in late summer, which suppresses reed growth; however winter cutting encourages reed growth and leads to such dominance that the reed can be harvested in bulk for thatching. Most fens are small, isolated and restricted to the margins of larger wetland systems; however large areas are still to be found in the Broads and the Cambridgeshire Fens.

Wet woodland

Mature wet woodland is a rarity in the UK and where it does exist it is often restricted to the margins of fens and marshes and the fringes of slow moving rivers. Typically dominated by alder or willow, it can be a species-rich habitat, especially where it occurs at one end of a complete transition from open water to woodland; a few such examples can be found in the Broads. Wet woodland also occur away from obvious water supplies, for instance in Suffolk where alder woods occur on the poorly drained plateau clays.

Water meadows and wet grasslands

Although often badly affected by agricultural improvement, these grasslands can form extensive systems in river valleys and the lower parts of river floodplains. Associated with traditional extensive grazing regimes, where intervening ditches are maintained as ‘wet-fences’, such grassland networks form some of our most intact wetland systems. Good examples can be found all around the country and include the Pevensey and Somerset Levels, the floodplains of the Itchen and Test rivers in Hampshire and the Thames in Oxfordshire and parts of the Broads in Norfolk and Suffolk. Many such systems support the last of our species-rich lowland meadows but even where these are not as good as they once were, the ditch networks that divide them up can still be rich in aquatic and marginal plants

Key issues

Perhaps the single most influential factor in the loss of wetlands is drainage. Wetland soils, particularly fen peats, make fine agricultural soils if the water can be got rid of. This has of course already happened across many tens of thousands of hectares of former wetland habitat, with unfortunate consequences in terms of soil loss through oxygenation and shrinkage, windblow and carbon release.

The flower-richness of wetland habitats is dependent also on good water quality. Where wetlands are fed by rivers which pass through towns and cities and intensively farmed agricultural areas, high nutrient concentrations in the water cause a few species to outgrow the majority, leading to a rapid decline in floral diversity.

Abstraction of water from underground sources can reduce supplies of water to spring fed systems such as valley fens and chalk-stream margins. This leads to a gradual drying out, loss of water-dependent species and ultimately to complete loss of the wetland habitat completely. Water-levels can often be restored quite quickly, with the withdrawal of abstraction, but this does not necessarily lead to a restoration of former vegetation, mainly due to the oxygenation and breakdown of formerly water-logged soils.

Changes in agriculture and the way people live their lives has led to a decline (and in some cases almost complete loss) in markets for traditional fen produce. This has led to fens becoming uneconomic to manage in the traditional way, leading to conversion to agriculture or abandonment.

What we're doing about it

Plantlife’s Fenlands Project, supported by Esmee Fairbairn and Natural England, conducted experimental management at a range of sites in the East of England to a) enhance populations of priority fen species and b) encourage the reappearance of fen plants at degraded fens. Experimental work finished in 2009 but monitoring work continues to track the response of plants to the experiments over time.

Fen Orchid Conservation Programme, supported by Natural England, working with partners to understand the ecology of the fen orchid and further develop its conservation strategy.