Fen Management Handbook - Scottish Natural Heritage

6.6 Re-establishment of fen vegetation
The previous sections describe methods for influencing the direction of habitat
change in fens where natural succession is causing the loss of features of interest.
Section 9: Creating Fen Habitat offers guidance on creation of entirely new fens,
often as part of larger wetlands.
Where fen is being re-created on sites that have been destroyed through past
human activities, such as drainage, the ability to re-establish characteristic fen
communities and the most suitable techniques to use, will depend on a number of
factors including:
– the length of time the fen has been drained;
– the plant species present in any refugia within the area to be re-wetted;
– the proximity of extant fen habitat with a similar species composition.
6.6.1 Regeneration from the seed bank
The number of characteristic plant seeds surviving in the seed bank decreases as
the length of time since the fen was drained increases. Only 4% of the seeds of fen
species persist in the seed bank after 10 years (Maas and Schopp-Guth, 1995).
Only the commoner hay meadow species persist in the seed bank where there
has been agricultural improvement of former fen sites. The rarer species of hay
and floodplain meadows have short-lived seed banks (Grootjans et al, 2002). The
species present in the seed bank can easily be determined by spreading large soil
samples out in seed trays and placing them in containers where the water level is
kept permanently high.
6.6.2 Refugia
Most species of fen plants have rhizomes by which they will spread into wet areas
vegetatively, as well as by seed. The speed at which fenland plants spread by
rhizome varies: for reed this is usually somewhere between 10 cm and 2 m per
annum. For those plants which do not readily produce viable seed, the deliberate
transfer of small (30 cm x 30 cm) turfs will help accelerate the re-establishment
of fen species. Care must be taken to cut turfs with sufficient depth of soil to
include the rhizomes. This technique should not be used if invasive alien species
such as parrot’s-feather (Myriophyllum aquaticum) and New Zealand pygmy-weed
(Crassula helmsii) are present on the donor site. Further guidance on planting of
vegetative propagules and seeding is included in Section 9: Creating Fen Habitat.
6.6.3 Proximity of extant fen
Colonisation by seed from nearby fens is unlikely to occur unless there are direct
channels along which vegetative fragments and seeds can float into the receptor
site. Aquatic plants appear to spread more readily between wetlands than sedges
and other emergent fen species. In North America (Johnson & Valppu 2003) it has
been found necessary to take plugs of sedges and other plants from nearby fens
to re-establish characteristic vegetation on cut-over fens. Turf removal to reduce
nutrient levels in the surface layers (see Section 8: Managing Fen Nutrient
Enrichment) removes the seed bank, making the re-establishment of species-rich
meadow vegetation unlikely, unless donor plants are available.
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