UK Lowland Wetland Habitat Types & Characteristics
Lowland Raised Bog
Raised bogs in the lowlands of Britain occur on elevated
deposits of peat and receive mineral nutrients principally from
precipitation. They are referred to as ombrotrophic (rain-fed)
mires.
This habitat is very acidic and nutrient-poor. It is also poorly
drained and water-logged. Because of these conditions the
decomposition of plant material is strongly inhibited. This results
in an accumulation of peat, which, over thousands of years, can
become many metres thick. The building peat raises the bog surface
upwards to form a gently-curving dome from which the term 'raised'
bog is derived. This dome can grow to 10m in height or so and
separates the bog from the underlying water-table, minimising the
inflow of ground-water. Bogs in which peat is being accumulated are
referred to as ‘Active’, whereas those in which peat formation is
at a temporary standstill (normally because of drainage) are
referred to as ‘Degraded’.
The vegetation of lowland bogs is very distinctive. It
includes a range of specialised wetland plants and varies depending
on the pattern of surface pools, hummocks and lawns. Usually
various colourful Sphagnum mosses predominate (e.g.
Sphagnum auriculatum, S. cuspidatum, S.
magellanicum, S. papillosum, S. recurvum).
These are highly absorbent and produce a characteristically
'spongy-feel' to the bog surface. Other typical plants include bog
asphodel Narthecium ossifragum, bogbean Menyanthes
trifoliata, bog-myrtle Myrica gale, cotton grasses
Eriophorum angustifoium and E. vaginatum,
cross-leaved heath Erica tetralix, deer-grass Scirpus
cespitosus, heather Calluna vulgaris, purple
moor-grass Molinia caerulea, round-leaved sundew
Drosera rotundifolia, and the white beak-sedge
Rhynchospora alba.
Raised bogs are home to numerous scarce lowland plant
species, such as the bog mosses Sphagnum pulchrum and
S. imbricatum, uncommon bog rosemary Andromeda
polifolia, cranberry Vaccinium oxycoccos, and the
great and oblong leaved sundews Drosera anglica, D.
intermedia. The vegetation is greatly affected by peat-cutting
and drainage, which tend to dry out the bog, encouraging purple
moor-grass and heather and allowing birch and pine trees to
invade.
Lowland raised bogs form an important refuge for many wetland
species. These include various breeding waders, wildfowl and birds
of prey, such as curlew, snipe, hen harrier, hobby and merlin. Many
species of invertebrates occur, including beetles, butterflies,
caddis flies, damselflies, dragonflies, mites, moths, spiders and
springtails. Some of these are highly localised in the lowlands,
including the large heath butterfly Coenonympha tullia
subspecies davus, the bog bush cricket Metrioptera
brachyptera, the mire pill beetle Curimopsis nigrita,
the white-faced darter Leucorrhinia dubia, and Britain’s
rarest caddis fly Hagenella clathrata.
Lowland Fen
Lowland fens are minerotrophic peatlands (i.e. their nutrients
come from ground water as well as rain water), that are at least
periodically waterlogged. Although they are underlain by peat,
decomposition tends to be relatively high and so the peat depth is
shallow and there is no peat dome (as with raised bogs). Fens are
complex and dynamic systems; they frequently form complex mosaics
with a number of associated habitat types, including wet woodland
(fen carr), reedbed, lowland heathland and lowland meadow.
Two broad types of fen can be distinguished. Topogenous fens,
where water movement is generally vertical – these include basin
fens and floodplain fens – and soligenous fens where water movement
is predominantly lateral – these include valley mires, springs and
flushes in the lowlands, mires associated with springs, rills and
flushes in the uplands, trackways and ladder fens in blanket bogs,
and laggs of raised bogs. In addition, fens are also described as
poor-fens or rich-fens (see below).
Poor-fens
Poor-fens have low to moderate fertility and are fed by acid
water (pH <5) derived from base-poor rocks or glacial till, such
as sandstones, granites or sand and gravel. They occur mainly in
the uplands or in association with lowland heaths. Their vegetation
is characteristically species-poor, with a moderate to high cover
of Sphagnum bog mosses (mainly Sphagnum
cuspidatum, S. palustre, S. recurvum, S.
squarrosum) and sedges (especially Bottle sedge Carex
rostrata), with a scattered and an impoverished layer of herbs
including, for example, common cotton-grass
Eriophorum angustifolium, devil's-bit scabious
Succisa pratensis and marsh cinquefoil Potentilla
palustris. In some instances Sphagnum can be scarce
and various Carex sedges dominate in a more herb-rich
sward with species like bogbean Menyanthes trifoliate and
marsh bedstraw Galium palustre present.
Rich-fens
Rich-fens are fed by alkaline, mineral-enriched, calcareous
waters (pH >5). They are mainly confined to the lowlands, but
also occur in the uplands where there are localised pockets of
base-rich rocks. The vegetation is normally relatively
species-rich. It includes mire vegetation dominated by a range of
Carex sedges, growing over a variable carpet of mosses and
mixed in with various vascular plants (such as bogbean, common
butterwort Pinguicula vulgaris, common cotton-grass,
lesser spearwort Ranunculus flammula, marsh cinquefoil,
marsh bedstraw, marsh lousewort Pedicularis palustris,
marsh marigold Caltha palustris, marsh thistle Cirsium
palustre, and ragged robin Lychnis flos-cuculi).
Other rich-fen mire communities are dominated by black bog-rush
Schoenus nigricans, growing mixed with blunt-flowered rush
Juncus subnodulosus and purple moor-grass Molinia
caerulea, cross-leaved heath Erica tetralix, bog
asphodel Narthecium ossifragum and a mixed cover of mosses
with Sphagnum as a consistent feature.

Rich-fens also support mixed tall-herb fen communities in which
Common reed Phragmites australis is predominant. These
usually include a range of tall herbs, such as hemp agrimony
Eupatorium cannabinum, marsh bedstraw Galium
palustre, meadowsweet Filipendula ulmaria, milk
parsley Peucedanum palustre, purple loosestrife
Lythrum salicaria, and yellow loosestrife Lysimachia
vulgaris. Much less common is tall, saw-sedge Cladium
mariscus dominated, species-poor, swamp vegetation. Some
rich-fens in the south-east of England support a kind of
species-rich fen-meadow, which is dominated by purple moor-grass
with an admix of carnation sedge Carex panicea,
devil's-bit scabious, marsh bird's-foot trefoil Lotus
uliginosus, marsh thistle and tormentil Potentilla
erecta.
Fen animals

Fens provide an invaluable habitat for a large number of wetland
animals. The invertebrate and bird fauna are particularly rich.
Numerous species of aquatic beetle, damselfly, dragonfly, fly,
moth, snail and spider are associated with fens. Rare invertebrates
associated with fens include Desmoulin’s whorl snail Vertigo
moulinsiana, the fen raft spider Dolomedes
plantarius, the lesser water measurer Hydrometra
gracilenta, the Norfolk Hawker dragonfly Aeshna
isosceles, the Pashford pot beetle Cryptocephalus
exiguus, the reed leopard moth Phragmataecia
castaneae, and the swallowtail butterfly Papilio
machaon. The bird fauna includes species such as bearded-tit,
bittern, Ceti’s warbler, little egret, marsh harrier, marsh
warbler, spotted crake and water rail. All of Britain’s amphibian
species occur in lowland fens.