Fen Management Handbook - Scottish Natural Heritage

Case Study 7.3
Fen Water Management
– New Forest Mires / Stony Moors
New Forest mires have elements which are typical of both bogs and fens. The
variation in vegetation composition is attributable to acidity and water regimes,
determined by underlying soils, hydrology, nutrient status, and management
particularly grazing and burning pressure. The New Forest supports approximately
2000 hectares of mire habitats, the structural variation is very wide and each mire
system is unique (SAC Management Plan).
Since the mid-19th century more than 70% of the New Forest mires have been
drained. This was either to further the establishment of trees in enclosures or to
reduce the water table and thereby ‘improve’ grazing on the Open Forest. These
activities varied greatly in scale, impacts on the habitats, and in their primary
purpose. New Forest peat is thin and rarely in excess of 2 m. This makes them
particularly vulnerable to damage from artificial drainage, causing rapid headward
erosion and lateral peat slumping.
The botanical diversity is attributed to the alkaline seepage in contact with an
underlying clay layer (Headon Beds). By contrast upstream, the acidic influence
of plateau gravels gives rise to permanently waterlogged, nutrient poor acidic
peat. It supports Sphagnum mosses with other bog species such as bog
asphodel (Narthecium ossifragum), common cotton grass and white-beak sedge
(Rhynchospora alba). ‘Soakways’ exist along natural drainage runnels of valley
bogs which are dominated by marsh St John’s wort (Hypericum elodes) and bog
pondweed (Potamogeton polygonifolius).
Stony Moors
Stony Moors (23 ha) supports fen and mire habitats well-known for their botanical
diversity, largely attributable to the base-rich influence of the underlying clay, which
is particularly obvious along the valley spring-line where seepage mires exhibit a
rare and characteristic marl flush community. Lime rich marl flushes, (pH around
7.0 or higher) support characteristic species including Eleocharis quinqueflora, the
brown moss Palustriella commutata, and the abundant brown moss Scorpidium
revolvens (Sanderson 1998).
At Stony Moors there was clear evidence of past drainage activities with incised
channels, headward erosion and localised spoil heaps. The drainage was likely
to have been 1930’s in origin, with some further works associated with the
construction of Holmsley Aerodrome in 1941-42. It is likely that soon after drainage
the drop in water table caused peat to oxidize releasing nutrients, thereby providing
temporary benefits to grazing livestock through increased productivity. However,
soon after this initial flush tree species such as willow, birch and pine were able to
colonise the degraded mire surface. As a result of this past drainage, secondary
woodland has been able to colonise parts of the mire and fen system and
associated stream corridor.
Management objectives
In 2005 the Forestry Commission undertook to restore this mire as part of the LIFE
3 Sustainable Wetland Restoration Project. Following significant consultation it
was agreed to fell the recent secondary woodland that was encroaching the mire
surface and to restore the mire by completely infilling the eroding drainage channel.
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