Fen Management Handbook - Scottish Natural Heritage

5.1 Why do fens need management?
In ecological terms, ‘fen’ is not a stablised ‘climax’ condition, but a transitional
habitat or seral stage in which pioneer plant communities are replaced by
successive colonists as part of the natural process of succession from open water
to mature woodland or ombrotrophic bog or dry land. This process of succession
results from interactions between both different species and between species and
their environment, and is highly variable both in terms of sequence and the time, in
some cases taking thousands of years. A more detailed explanation is included in
Conserving Bogs – The Management Handbook (Brooks and Stoneman, 1997).
Favourable condition of fens in nature conservation terms was once a consequence
of economic management. Cutting fens for hay and aftermath grazing, for example,
prevented the sward becoming dominated by a few vigorous plants, such as
reed, reed canary grass, reed sweet grass and bulrush and was responsible for
producing and maintaining many traditional fenland landscapes.
As a result of the reduction in traditional management such as reed-cutting and
the production of bog hay, many fens have been abandoned. Without active
management, most fens are quickly colonised by scrub and trees, a process that is
accelerated by nutrient enrichment and drainage around or within the site. The fen
carr or woodland that develops has wildlife interest but cannot support many of the
species of open fen.
In a completely natural system, rivers meandering across their floodplains and
flooding continually re-create fen habitats. This natural dynamism also enables
fluctuation of fen vegetation communities between sites without overall species
loss. Human activity in the form of agricultural improvement, river engineering and
urbanisation has, over the centuries, fossilised many of our rivers and wetlands,
particularly in lowland Britain. Many of our lowland fens are now moving towards the
end-points of natural wetland succession, often hastened by land drainage, siltation
and nutrient enrichment. Maintaining the conservation interest of many wetlands
depends on deliberate management to interrupt the process of succession or revert
the fen to earlier successional stages which support increasingly uncommon plants
and animals such as fen violet, fen orchid and swallowtail butterfly.
Management and restoration of fens for conservation usually aims to maintain the
species composition of a fen community at a specified stage along the natural
transitional process from open water to mature woodland or bog, which can only
be achieved by intervention, in the form of management. Management aims should
include the maintenance of the habitat mosaic for birds and invertebrates, as well
as for the plant communities. The following section describes all the factors to be
considered when drawing up objectives for fen management.
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