Restoration of mires and wet grasslands - Restoration Ecology - page 111

9

Restoration of mires and
wet grasslands

Ab P. Grootjans, Rudy van Diggelen and Jan P. Bakker

9.1 Introduction that of a fen meadow. The fen then shifts from a peat-

accumulating system to a peat-degrading system.
Fens and fen meadows have many species in com-
mon. Fen meadows are usually more rich in species,
because after slight drainage many typical fen species
remain and many typical grassland species establish
themselves in the area. While bogs and fens are peat-
accumulating systems, semi-natural fen meadows do
not accumulate peat. There has been a strong decline
in semi-natural fen meadows and related species-rich
grassland in north-west Europe as a consequence of
changes in agricultural practices during the past
decades. Estimates from the UK are that 95 -98% of
species-rich hay meadows that were present before 1940
have been lost due to intensification of agricultural
exploitation or due to abandonment and subsequent
development of forest (Garcia 1992, Muller et al. 1998).
We use the notion wetland as a general term, to
describe an area with vegetation adapted to very wet
conditions. A wetland may or may not be a peatland;
it can also occur on mineral soil. A peatland is a soil
type consisting of dead organic material that has
been formed on the spot (sedentarily) and which con-
sists of at least 30% dry mass of organic material.
In this chapter we will mainly discuss two types of
restoration project: (i) projects that try to restore
damage in existing nature reserves, and (ii) projects
that try to increase the biodiversity in peat areas which
are no longer destined for intensive agricultural pro-
duction and where new nature is being developed by
increasing water tables and flooding frequencies and
sometimes by removing the eutrophic topsoil entirely.

Mires are peatlands where peat is currently being
formed (Sjörs 1948). In Europe loss of mire area has
been particularly great in north-western and south-
ern Europe since c .1900. Here less than 1% of the
original mire area has remained in most countries
(Joosten & Clarke 2002). In eastern European coun-
tries, such as Poland, Belarus, Estonia, Latvia and
Ukraine, between 10 and 50% of the former mire area
has remained, while in European Russia, Sweden,
Norway and Romania the mires have been best pre-
served (> 50% of the mires remaining). On a world scale
mire losses are highest in Europe due to its high popu-
lation pressure on nature and the climatic suitability
for agriculture and forestry. In the non-tropical world
80% of mire losses are attributed to agriculture and
forestry. Peat extraction in the world is responsible
for c .10% of mire losses, but on an annual basis new
peat extractions commence in some 10 km 2 (Joosten
& Clarke 2002). In North America and Asia mire
losses are much lower (5 and 8% respectively).
Mires can be roughly divided into bogs and fens.
Bogs are generally considered as mires raised above
the surrounding landscape and fed by precipitation
(rainwater), whereas fens are usually situated in
depressions and, additionally to precipitation, they are
also fed by ground or surface water. Bogs are always
acidic (pH < 5.5), whereas fens are usually base-rich
and slightly acidic or neutral (pH > 5.5; Succow 1988,
Wheeler et al. 2002). Most fens have been slightly
drained in Europe and the vegetation has changed to

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