Raised mire
Raised mire is an extremely local type
in Britain, restricted to those areas where
conditions have allowed topogenous flood-plain mires to develop ombrogenous
surfaces. The former occurrence of raised mire at Holme Fen in the
Huntingdonshire Fenlands suggests that this type can develop even under low
rainfall when the original topogenous mire begins to grow above the influence of
nutrient-rich ground water. Extensive peat-cutting has destroyed the raised mires of
the Somerset Levels, but areas of secondary vegetation have developed in cut-
over areas at Shapwick Heath and adjacent areas, especially Westhay Moor.
These vary from small areas of ombrogenous communities, through Molinia-Myrica
types to remnants of rich-fen. The whole complex (P.241 merits grade 1 status on
entomological, floristic and ornithological grounds. Similar conditions are found at
Thorne and Crowle Waste in Yorkshire. At one time very extensive raised mires
occurred there and at Hatfield Moors but these have been destroyed or severely
modified by peat-cutting and have lost their former importance as intact raised
mires. However, the variety of habitats represented within the parts of Thorne and
Crowle Waste cut over during the nineteenth century makes this an important
peatland site (P.60, gr. 2). It has considerable floristic and entomological interest
and bird populations are particularly important because of the large extent of semi-
natural vegetation.
The most southerly raised mires in Britain
which are reasonably undamaged are in
south Wales. On the south side of the Dyfi estuary, in Cardiganshire, Cors Fochno
(Borth Bog) (P.29, gr. 1*) has developed over estuarine sediments and has the
largest and most important area of undamaged raised mire surface now remaining
in Britain. Extensive Sphagneta occur here and the characteristic raised mire
features of drier rand and more base-rich lagg are well represented. The mire flora
is rich and contains a blend of southern and northern elements. Farther south-east
and inland, Cors Goch glan Teifi (P.30) in the same county is an extensive raised
mire system overlying an ancient Late-glacial lake which once occupied the broad
Teifi valley. The argest patch of raised mire lies to the west of the Teifi, and ! is
sufficiently different from Cors Fochno to merit grade 1 j status as well. The
classical raised mire features of central i cupola, with marginal rand and laggs are
finely developed here, and the stratigraphy shows an equally classical
developmental history. Locally there are pool and tall hummock
systems giving
a patterned surface not found on Cors Fochno, and the range of communities is
greater, probably because of local drying.
Still farther inland and at a higher elevation
(260 m), Rhos Goch in Radnor (P-3i)
differs from the previous two mires and is also placed in grade i. It is smaller, with
well-developed lagg, but has a pool-hummock system of unusually large vertical
amplitude and shows an interesting association with valley mire, with continuity
between the two systems. The whole complex is floristically rich. There are a few
other raised mires of regional importance in Wales, such as Arthog Bog on the
Mawddach estuary in Merioneth, but north Wales is on the whole too mountainous
to give a terrain favouring the formation of this kind of mire.
In the west Midlands,
the drift-covered Shropshire- . Cheshire plain, with its
important concentration of basin mires, also has at least two notable raised mires.
The extensive Fenns Moss is worked commercially for its peat and is no longer of
national importance. By contrast, the rather small Wem Moss (P.40) in Shropshire
is important for its ; remaining area of undamaged surface with large amplitude
pool-hummock system, and finely developed mesotrophic lagg; there is also a rich
mire flora. Wem Moss resembles Rhos Goch in some of these features, but is
regarded as sufficiently important to rate as grade 1 in addition.
North-western England is one of the most
important regions in Britain for raised
mires. Inland, in Craven, Tarn Moss at Malham forms an ombrogenous component
in an important complex of predominantly calcareous wetlands ; and, on its own,
merits only bonus ranking. The main areas of raised mire are coastal. At the head
of Morecambe Bay on coastal flats beside the estuaries of the Kent and Lune are a
number of raised mires, all more or less severely disturbed and somewhat
degenerate. Foulshaw Moss has dried out and is now partially afforested. Some
remaining raised mires, notably those along the east side of the Leven estuary, are
nevertheless important entomologically, especially for Lepidoptera, and this
feature is partly related to their geographical position. Thus, although it
has been
strongly modified, the raised mire complex adjoining Roudsea Wood : (Fish House,
Deer Dyke and Stribers Mosses (P.47)) , is regarded as a grade 1
site.
Farther inland and to the north, Meathop
Moss has similar entomological interest,
but is rated grade 3. In the same area of southern Lakeland the existing NNR of
Rusland Moss is a partly dried-out raised mire thickly grown with Scots pine. Since
its notable features would seem to be duplicated by the larger and more important
Kirkconnell Flow in southern Scotland, grade 3 is the appropriate status for this
site. From its proximity to Merlewood Research Station, however, Rusland Moss
may have considerable potential as a woodland and mire research site.
On both sides of the Solway Firth, extensive
series of raised mires have developed
over plains of former marine sediment. On the Cumberland side the main areas are
around Kirkbride to the west of Carlisle. Reclamation and peat-cutting have caused
marginal contraction of remaining areas and destroyed most of the original natural
boundaries with laggs. Until about 30 years ago, several separate patches of
raised mire retained a largely undisturbed Sphagnum-covered surface, but since
then repeated fires and commercial peat winning have destroyed these surfaces to
the point where only two good examples remain.
The best remaining raised mire on the
Cumberland side of the Solway is Glasson
Moss north of Kirkbride. The southern part of this mire was cut commercially for
peat and has dried out to give a heather-dominated vegetation. Despite occasional
fires, the northern part still has a fine area of undamaged Sphagnetum with small
amplitude hollow-hummock system, and a rich mire flora. There is some
resemblance to Cors Fochno but the southern element in the mire flora is lacking,
and undamaged lowland Sphagnetum is now so rare in Britain that Glasson Moss
is also regarded as a grade 1 site (P.48). Wedholme Flow to the south of
Kirkbride, the other area with undamaged Sphagnetum, is now smaller than at
Glasson and so surrounded by a cut or modified peat surface that its viability is less
certain. Nevertheless, it is of some national importance and is given grade 2 status
(P.62). Bowness Common (P.61) is a large raised mire system immediately west
of and once continuous with Glasson Moss. It has been repeatedly burned and,
although some parts of the surface have a high Sphagnum cover, it cannot be rated
as more than grade 2. (But see Appendix regarding all the above sites.)
Drumburgh and Fingland Moss to the east
and Oulton Moss to the south are too
modified to merit selection (but see Appendix). Orton Moss, just west of Carlisle,
was probably originally a raised mire in part, but is now a complex of dry to wet
woodland with much poor-fen and fragments of acidophilous mire communities
mainly in old peat-cuttings. East and north of Carlisle, Scaleby Moss and Todhills
Moss are much cut and severely dried raised mires with Sphagnetum only in old
peat-cuttings, and Solway Moss near Gretna has been so ravaged by commercial
peat-cutting that virtually no undamaged surface is left; pine colonisation is also
widespread here. Scaleby Moss has an .important Quaternary sequence to which
the technique of radio-carbon dating was first applied in Britain, and it is thus a
classic site in this field. Farther inland and at slightly higher levels (90 m) around
Hethersgill in north Cumberland, are acidic peat mires which appear to be
transitional between raised mire and blanket mire. These have deteriorated in
recent years, mainly through large-scale peat-cutting, and though there are still
good areas of Sphagnetum locally, they cannot be rated more highly than grade 3.
Bolton Fell is the best of these intermediate mires.
The parallel series of raised mires on
the Scottish side of the Solway has also
undergone extensive deterioration in recent years. Much of the large Lochar Moss
near Dumfries has dried out through repeated burning and the best remaining area,
Racks Moss, has been afforested. Mosses east of Annan, such as Nutberry Moss,
are degenerate also. The best remaining example of these Scottish Solway raised
mires is Kirkconnell Flow on the Kirkcudbrightshire side of the Nith estuary. It is
extensively colonised by pine and birch, and the former has spread greatly in recent
years. Despite local drying, much of the bog centre is wet and Sphagnum-
dominated, though its surface structure is quite different from that of Glasson Moss.
Kirkconnell Flow is regarded as a grade I site (P-70) mainly for the interesting
combination and relationships which it shows between the two quite different
formations, woodland and raised mire.
Farther west, Auchencairn Moss in Kirkcudbrightshire
and Moss of Cree in
Wigtownshire are too strongly modified to rate highly but several small raised mires
in this area are of grade 3 status, e.g. Carsegown Moss near Wigtown.
In the central Lowlands of Scotland many
mosses are intermediate between raised
and blanket mire in their morphology. Most have been severely modified by human
disturbance but two examples merit grade 2. These are Blawhorn Moss, West
Lothian (P.76), which still has an active Sphagnum surface, and Dogden Moss
within the grade 2 site known as Greenlaw Moor (P.78). This site is rather more
modified by grazing but has a good chance of recovering a Sphagnum-dominated
surface under suitable management.
In the upper Forth valley between Stirling
and the Highland Boundary Fault there
was at one time a vast area of raised mire development, two large areas of which
still remain intact, the remainder having been cut away in the past. A complex of
mires known as West Flanders Moss is now largely planted with conifers but the
single area known as East Flanders Moss (P.89) still has characteristic raised mire
vegetation. It has suffered to some extent from drainage and periodic burning and
the communities are considerably more modified than those of Cors Fochno and
Glasson Moss. This site is considered to be nationally important morphologically
and appropriate conservation measures could probably restore the Sphagnum
cover so that grade 2 status is indicated. Other smaller Mosses to the south of the
Forth are rated grade 3. In Loch Lomond the island of Inch Moan has a covering of
peat which can be regarded as an unusual type of raised mire, bounded by the
rocky shores. Typical communities have re-established themselves after further
peat removal. This site is best regarded as another unit in the grade 1 island
complex of Loch Lomond and is treated as a bonus to the woodland site (W.i69).
In eastern Scotland, areas of lowland
peat moss on the plains of Angus and
Aberdeenshire evidently represent former raised mires or intermediates between
this type and blanket mire. Nearly all are severely modified and many have dried
out through excessive disturbance. There is, however, a most unusual example of
high-altitude raised mire, Dun Moss at 350 m in the Forest of Alyth, Perthshire. This
site (P.84) shows a classic raised mire developmental history and has a well-
developed lagg; the surface has a Sphagnum-dominated hummock-hollow mosaic
and a greater abundance of lichens than any other raised mire in Britain. Dun Moss
thus has some features of blanket mire, reflecting its altitude and geographical
position, and is an extreme type in the national series, meriting grade 1.
In the western Highlands, on the borders
of northern Argyll and Inverness-shire,
there is a fine series of raised mires known as Claish Moss (P.94) on level ground
beside Loch Shiel. There are striking surface patterns of aligned pools with
intervening ridges on the individual mires, and many of the pools are in a mature
phase, showing signs of linking up with each other. Well-developed marginal rands
are present and lagg streams separate the individual mires. This is one of the most
spectacular mire systems in Britain, and amply deserves grade 1* status. Kentra
Moss (P. 102) is best regarded as a westward extension of Claish Moss on coastal
flats, but is in a more modified state and, though important, is regarded as grade 2.
Farther north along the west coast, Blar na Caillich Buidhe (P. 103) has developed
on low ground adjoining Loch Morar. This area has a patterned surface similar to
that of Claish Moss but has been more disturbed and is rated as grade 2.
Blanket mires
As blanket mire development depends not
only on a cool, wet climate, but also on
suitable topography, it is best developed in those parts of western and northern
Britain where the uplands are gently contoured, with broad, flat watersheds falling
away very gradually into the low country. Many upland sites have, in fact, been given
grade I or 2 rating partly for the blanket mires which they contain; in some instances
these mires rate as nationally important in their own right, though most are to be
regarded as bonus in value, and an integral part of total site diversity. For
convenience, most of these blanket mires are described in Vol. 2 under the upland
key sites to which they belong.
In southern England, the only blanket
mires are on the moorlands of the south-west
peninsula; those of Exmoor and Bodmin Moor are shallow in peat depth, relatively
dry and unimportant, but the plateau land of Dartmoor at over 430 m has a large
expanse of this peatland. It seems necessary to represent this most southerly
British occurrence of blanket mire in the national series of key sites, and an area of
north Dartmoor around East Dart Head and Cranmere Pool has been chosen for its
range of diversity as a grade 1 site (P.25). This area falls within the North Dartmoor
site rated as grade i for its range of variation from lowland heath to upland moor.
On the southern part of Dartmoor, the area of blanket mire around Cater's Beam is
less varied but is still regarded as nationally important (P.28, gr. 2).
In south Wales many of the upland plateaux
have a covering of blanket mire, but this
is mainly rather shallow and dry, and has no particular ecological interest. A good
example of patterned blanket mire occurs, however, within the Cwm Ystwyth grade i
upland site at Gors Lwyd, and other areas of mire between there and Teifi Pools
rate as bonus. The plateau mire of Cors Goch (P.34) in Radnor is one of the best
examples of this peatland in the region and is given grade 2 rating. Within the
Mynydd Du grade 2 upland site there are also quite good areas of typical Pennine
blanket mire. In north Wales, the eastern upland massif of Y Berwyn (11.13)
contains a varied range of high-level blanket mire, also of the Pennine Calluna-
Eriophorum type, with the southernmost stations for Rubus chamaemorus. The
Carneddau, within Eryri (U.10) have quite large areas of Juncus squarrosus mire on
shallow peat, a distinctive oceanic type. There are numerous patches of Sphagnum-
rich mire within Rhinog (U.I2) which probably complete the range of variation for
this formation in north Wales. The Migneint and Denbigh moors have quite
extensive areas of blanket mire, but these are only of regional importance.
In the Midlands, the gritstone moors of
the High Peak have large areas of blanket
mire, and this covers a significant part of the Kinder-Bleaklow grade 1 upland site,
ranking here as a nationally important example of a regional facies of Calluneto-
Eriophoretum in its own right (P.41, gr. 1). These Peak District mires are
characterised by the great depths of peat, local severity of erosion and abundance
of dwarf shrubs other than Calluna. The Pennines farther north have huge expanses
of blanket mire though much of this is eroded or severely modified, with dominance
of Eriophorum vaginatum and low cover of Sphagnum. The once fine blanket mires
of Stainmore have been much damaged in recent decades, and no longer have
large areas of Sphagnum carpet. The best remaining areas nevertheless appear to
lie within the Alston Block, and four grade 1 upland sites here have important
blanket mires. Moor House with its outlying extension of Yad Moss (P.50, gr. 1*)
shows a wide range of high level facies, from those with continuous Sphagnum
carpet to others severely degraded by erosion: these rate as nationally important.
Appleby Fells and Upper Teesdale also contain significant areas of blanket mire
and Mallerstang-Swaledale Head is interesting for its evidence of the full cycle of
peat erosion and regeneration.
By far the best undamaged Sphagnum-dominated
blanket mires outside Scotland
are on the great flat and gently undulating moors lying between the River North Tyne
in Northumberland and the River Irthing in Cumberland, at the south-western end of
the Cheviot Hills. The altitude here is considerably lower than at Moor House.
Although these moors have been extensively afforested in recent years, several of
these flows (level expanses of mire) have remained undisturbed and, because of
the widespread disappearance of such ecosystems elsewhere, are now of the
highest national importance. Each of these Border flows differs from the others in
some noteworthy feature, and to represent the range of topographical, structural,
hydrological and vege-tational variation, a group of five have been rated as an
aggregate grade 1* site (P.49): Butterburn Plow, Haining Head Moss, Hummel
Knowe Moss, Coom Rigg Moss and Felecia Moss. Of the many others, two,
Falstone Moss (P.63) and Gowany Knowe Moss (P.64), are designated alternative
grade 2 sites. Elsewhere in Northumberland, the flow of Boddle Moss in the
Simonside Hills, the watersheds of Kielderhead Moors, pockets of mire on the
Harbottle
Moors and the peat-covered summit of the
Cheviot itself are bonus areas of blanket
mire in grade 2 upland sites.
In the Southern Uplands, a broad valley
in the Galloway hills contains a fine linear
series of Sphagnum-dominated Trichophorum-Eriophorum mires with patterned
surfaces, ranging from a type approaching raised mire to typical blanket mire. This
complex, known as the Silver Flowe (P.71, gr. 1*) and contiguous with the Merrick-
Kells (11.35) upland site, is one of the most important mire systems in Britain.
Farther west in Galloway the extensive peat-covered areas of Wigtownshire have a
vegetation intermediate between that of raised and blanket mire (see Appendix).
Much of this district has been afforested in recent years and few good quality
blanket mires remain. Two grade 2 sites are selected which include the range of
conditions in this area. These are Kilquhockadale Flow (P.79) and the blanket
mires around Mochrum Lochs (P.77). The Cairnsmore of Fleet grade i upland site
contains typical examples of western blanket mire with abundant Molinia and
Trichophorum, mostly on shallower peat. On the watersheds of the Moorfoot Hills at
the eastern end of the Southern Uplands are good examples of little disturbed
Sphagnum-rich Calluneto-Eriophoretum mire with abundant Rubus chamaemorus;
these merit grade i status in their own right (P.72). Adjoining the western end of the
Cheviots, the Langholm-Newcastleton Hills (U-38) also have a very similar complex
of watershed blanket mire. In the same district, the much lower-lying Fala Flow
(P.80, gr. 2) in Midlothian is an isolated area of rather dry blanket mire with
considerable wildfowl interest.
Pennine-type Calluneto-Eriophoretum blanket
mire is very extensive in the eastern
Highlands, and high level examples are well represented in the series of upland key
sites, e.g. Drumochter Hills (11.45) and Monadhliath (U.58). Really montane
examples, in which Empetrum hermaphrodi-tum replaces Calluna, are present in
the Cairngorms (U-44) and Caenlochan-Clova (U-42). The most distinctive vege-
tational feature of blanket mire in this district is the occurrence of a lichen-rich
facies of Calluneto-Eriophoretum, and the large mire-crowned plateau of Carn nan
Tri-tighearnan 16 km east of Inverness, has been chosen as a grade 1 site (P.86)
specifically to represent this feature; the Ladder Hills (P.90) much farther east are
regarded as a grade 2 alternative. The great basin of Rannoch Moor on the
borders of the eastern and western Highlands, in Perthshire and Argyll, contains an
extremely wide range of variation, not only in blanket mire but also in valley, basin
and soligenous mires. The blanket mire here is of the low-level, western type
(Trichophoreto-Eriophoretum). Part of this complex has been selected as a grade
1* site (P.85). Gull Nest (P.91) in Moray is included as an eastern grade 2 example
of a mire system with markedly western features, notably a patterned surface.
The Highlands west and north of the Great
Glen have the largest continuous areas
of blanket mire in Britain. Owing to the extremely wet climate over all but the far
eastern parts of this region, blanket mire is extensively developed at low levels
(down to sea-level locally). By contrast, many of the higher mountains, especially in
the west, are characterised by sharp relief, so that high-level blanket mire is less
well represented than in the eastern Highlands. Some of the islands, notably Lewis
and Shetland, are covered largely by blanket mire, but the biggest expanses are in
the flow country of east Sutherland and Caithness, where an area of roughly 2500
km2 from Strath Naver eastwards is covered mainly by this type of peatland. This
last district has the largest areas of undamaged Sphagnum-rich blanket mire in
Britain, and the conservation of representative examples of the range of variation is
of the highest importance.
Within the Sutherland-Caithness flow country
two morphological types of blanket
mire have been distinguished, namely, peat-covered watersheds and valley-side
mires which exhibit marginal features resembling those of raised mire. The
watershed flows are by far the most extensive and typically show numerous
irregularly shaped deep peat pools on their relatively level surfaces. The second
type occurs marginally to these but has a more restricted occurrence ; it is a gently
sloping mire surface with linear patterns of ridges and hollows aligned parallel to
the contours. Two vegetation types have been distinguished in these flows, the
western Trichophoreto-Eriophoretum and a representative of the higher level and
more eastern Calluneto-Eriophoretum, locally rich in northern dwarf shrubs and
lichens, but usually lacking Rubus chamaemorus. On strongly modified ground there
are locally extensive Trichophorum cespitosum communities.
The finest example of watershed patterned
mire is the great flow of Blar nam
Faoileag (P.95) in Caithness, covered with the eastern type of vegetation and with
a spectacular development of pool-and-hummock patterned surface. This is one of
the most important mire sites in Britain, and rates as grade 1*. The nearest
equivalent is the flow a few kilometres to the east, containing the Dubh Lochs of
Shielton. The pools here are less numerous than on Blar nam Faoileag, and the site
as a whole is less extensive and varied in floris-tics, and it is regarded as an
alternative grade 2 site (P. 104). A third, more dissected system of typical
watershed mire, still in a relatively undisturbed state, occurs on the moorlands west
of Forsinard (P. 105) at the head of Strath Halladale. Separate patches of pool and
hummock mire occur in a general expanse of drier and more disturbed blanket
mire. This area contains the grade 2 upland site of Ben Griam More and Ben
Griam Beag. The most extreme type of watershed blanket mire occurs slightly to
the east on the other side of Strath Halladale. The Knockfin Heights (P.98) on the
marches of Sutherland and Caithness are a moorland tract with a large area of
plateau watershed studded with pools and dubh lochans of larger size than usual. In
places, maze-like systems of peat lochans have developed by the breakdown of
the ridges between separate pools; the intervening mire is mostly in a senescent
phase of growth, and the whole complex may represent a final stage of
development of blanket mire. Part of this watershed is rated as grade 1.
The best examples of valley-side flow
yet found are near the head of the Strathy
River (P.96) where a group of four relatively undisturbed sites has been chosen as
an aggregate grade 1* site. These four areas are essentially undamaged pool and
hummock systems in a continuous expanse of more disturbed blanket mire which
contains degraded examples of similar type, and a boundary has been chosen to
include this intervening ground as a buffer zone against further damage. All four
mire areas differ in morphology, including pool-hummock features. The same area
also contains a good example of watershed flow which should be included in the
site. Another example of valley-side mire and an associated mire of intermediate
type near Loch Badanloch in the same district might be regarded as a less varied
alternative site to the Strathy River Bogs, and is linked to the Forsinard grade 2 site
(P. 105).
An area of moorland in the Southern Parphe
(P.97, gr. 1) in the extreme north-west
corner of Sutherland, has been chosen to represent the most oceanic facies of the
range of patterned blanket mire. It includes good examples of watershed and valley
side flows, and several areas of sloping mire surface with pronounced linear
patterns. The area also contains an important example of northern valley mire, and
forms part of a larger site rated as grade 1 for its upland interest, especially the
marked altitudinal descent of montane vegetation. The coastal margin of the area,
with extensive cliffs and dunes at Sandwood, is also regarded as a grade 1 coastal
site. Farther east in Sutherland, on the large tongue of moorland known as
A'Mhoine between Loch Eriboll and the Kyle of Tongue, are areas of patterned
watershed mire with numerous peat lochans. The ground is Sphagnum-rich in
places but, more unusually, some areas show local dominance of lichens, a feature
usually associated with continental conditions. There are also patches of dwarf-
shrub-rich mire and low-level occurrences of montane dwarf-shrub heath on Ben
Hutig. The site (P.106) is rated as grade 2.
Several grade 1 upland sites in the western
and northern Highlands have significant
areas of blanket mire which fall into the bonus category. The island of Rhum has
extensive areas of western Trichophoreto-Eriophoretum which locally contain a
good deal of Schoenus nigricans and thus show a similarity to the blanket mires so
characteristic of western Ireland. The Inchnadamph and Beinn Dearg-Seana
Bhraigh areas have a good deal of blanket mire, especially the Calluneto-
Eriophoretum type. The Inver-polly and Foinaven-Meall Horn areas have extensive
but somewhat dissected complexes of low-level Trichophoreto-Eriophoretum,
including numerous patches of patterned mire. The Hermaness coastal grade i site
has a good deal of the Shetland type of blanket mire with a facies of Calluneto-
Eriophoretum on rather shallow peat. Finally, Ben Wyvis has some of the best
examples of blanket mire rich in montane dwarf shrubs, and these are regarded as
having grade 1 importance in their own right (P.99).
Flood-plain and open water transition
mires
Flood-plain mire is not well represented
in the extreme south of England, probably
as the result of draining the river valleys of their original swampland, but a good
example occurs at Stodmarsh (P.I, gr. 1) in Kent, where coalmining subsidence has
caused extensive flooding along the valley of the Great Stour, and produced an
area of open water and rich fen with especially high ornithological interest. The best
examples of these types of mire are concentrated in two districts of East Anglia, the
Norfolk Broads and the Fenlands. Broadland is a low-lying district in eastern
Norfolk where several shallow river valleys contain extensive tracts of fen and carr
which represent the most important area (c. 3300 ha) of flood-plain mire now
remaining in Britain. By contrast, the once vast mire system of the Fenlands south
of the Wash has been drained almost out of existence.
The Norfolk Broads fenland has survived
mainly as a result of continued exploitation
for various fen products. Indeed, much of the present habitat diversity, unique in
British ecosystems, is due to various forms of exploitation in the past. Peat was cut
extensively along the Norfolk river valley fens during the twelfth and thirteenth
centuries. A gradual rise in sea-level of about 3 m during the fourteenth century
caused periodic and increasing tidal inundation of the peat workings, which were
regularly 3-3.5 m deep. In the face of this adversity, the industry waned and the
flooded peat-cuttings were eventually abandoned, thereby forming the Broads.
Subsequent peat extraction produced extensive shallow turf-ponds, generally less
than 1 m deep, a large number being of relatively recent origin. Many of the
shallower areas of open water have silted up to the critical point where reed-swamp
can spread throughout, and in many places the succession proceeds to alder carr.
Only the deeper broads remain as sheets of open water.
Although very large areas of the flood
plain, especially in the lower sections of the
river valleys, have been reclaimed for summer pasture, much of the fenland has
been retained and exploited for reed (Phragmitescommunis), sedge (Cladium
mariscus) and marsh-litter consisting of mixed fen (tall herb and sedge)
communities. Many areas which would normally progress to carr were maintained
as open fen by these practices. However, this industry has declined considerably
during the last 40 years, with the result that large areas of mowing marsh and fen
have changed to carr and woodland. Ellis (1965) has emphasised that almost all
the specialised insects and other invertebrates, as well as the plants of the
Cambridgeshire Fens are represented in the artificially-maintained communities of
Broadland. There is a very real danger that, should the present trend continue,
much of the ecological value of this area will be lost under a blanket of alder carr.
Open fen and carr communities show considerable
floristic differences from one
river system to the next, the most pronounced distinction being between the Yare
and the northern rivers. These and other differences such as the extent of tidal
influence and even the local effect of salinity, and the variation in past land-use on a
local scale are in some cases so great that no single site can be regarded as
representative of the Broadland ecosystem as a whole. The total variation is such
that four grade i sites are chosen to include a reasonable representation of both the
range of edaphic and other habitat conditions, vegetation, flora and the specialised
fauna for which the area is famous. The open waters and aquatic macrophyte
communities are considered in Chapter 7.
The four areas selected are the upper
section of the Bure Marshes (P.7), the
Surlingham-Rockland section of the Yare valley (P.8), Button Broad (P.g) on the Ant
and the Hickling-Horsey area on the Thurne (P.6). The first three are primarily
selected on vegetational grounds whilst the Hickling-Horsey system is an
internationally important complex of habitats including some large tracts of rather
uniform and floristically poor reed-beds which provide the necessary habitat for
many marshland birds and insects. It is also important for its open water broads,
and there are nuclei of acidic mire with Sphagnum. In addition, Calthorpe Broad
(P.10), which is isolated from the main river systems and therefore less polluted, is
also chosen as a grade 1 mire/open water site. Barton Broad and Reedham Marsh
(see Appendix) (P.20) on the River Ant are an alternative site to the Bure Marshes.
Upton Broad is a grade i open water broad and has bonus interest for its fringing
reed-swamp (see Appendix). Many other areas of high scientific interest are
scattered throughout Broadland and the whole must be regarded as a nationally
important wetland complex.
The Fenland is an area of almost completely
flat land covering 3800 km2 at about
mean-tide level, south of the Wash, in Huntingdon and Peterborough,
Cambridgeshire, Lincolnshire and Norfolk. Essentially this is a shallow basin filled
on the northern side with silts and clays of estuarine origin and on the landward side
with peat which is the only visible evidence of a once vast flood-plain mire. The
area was almost completely drained by Dutch engineers during the seventeenth-
nineteenth centuries, and only fragments of the former mire vegetation remain.
Because of shrinkage of the surrounding drained peatland, these isolated
fragments now lie above the general level of the land and are therefore subject to a
hydrological regime quite different from that which caused their development.
Wicken Fen (P. 14) and Woodwalton Fen (P. 12) are the two most extensive areas
of relict fenland now surviving. Holme Fen is another such area, where
ombrogenous raised mire surface has developed, but become almost completely
colonised by birch, so that only fragmentary mire communities remain. Chippenham
Fen (P. 13), on the fringe of the true Fenland at a slightly higher level (26 m), is
springfed and so has a hydrological regime quite different from that of the first two
sites.
The present condition of these surviving
fen areas is entirely the result of human
activity. Chippenham Fen is the least dependent on artificial maintenance of the
water table, but even here succession to ash woodland has occurred over much of
the site. Nevertheless these areas are nationally important since they form refugia
for relict populations of plants and invertebrate species which have a very restricted
distribution in Britain. The invertebrates (especially insects) have been investigated
in detail, so that the fauna is unusually well known. In view of their all-round
ecological and historical importance Woodwalton Fen, Wicken Fen and
Chippenham Fen are all rated grade 1. The periodically flooded grade i neutral
grassland complex of the Ouse Washes in the Cambridgeshire Fenlands also has
reed-swamp in places, and there are intentions of creating more swamp within
existing reserves here, so that the area has bonus value in regard to flood-plain and
open water transition mire. Similarly, the grade 1 site of Sibson Meadows (L-73) on
the flood plain of the River Nene in Huntingdon and Peterborough has rich-fen
communities in places.
In Breckland, many of the meres and smaller
ponds have fringing fen vegetation
with bonus interest, and on the flood plain of the River Lark, an extensive rich-fen
and willow carr adjoin the Cavenham-Tuddenham Heath grade i site (L.6i(a)). On
the Suffolk coast on either side of Dun-wich, at Minsmere and Walberswick, two
river valleys dammed by coastal accretion at their mouths have developed
extensive reed-beds which are of outstanding importance for breeding birds, and
are associated with areas of acidic heath, scrub and woodland in a composite
grade 1* site (P.n).
Vegetationally, there is a good deal in
common between all the East Anglian mires
which are influenced by base-rich water, regardless of their morphological type.
Mesotrophic to eutrophic basin, valley, open water transition and flood-plain mires
overlap a great deal in range of plant communities, but certain vegetation types
belong mainly to a particular morphological type of mire, e.g. the calcareous 'brown
moss' carpets with low-herb sward are found mainly in valley mires.
Elsewhere, open water transition mire
is widespread, occurring wherever there are
lakes and tarns, and so is best represented in north Wales, northern England and
Scotland. Flood-plain mire is more local and usually of limited area, for many
former examples have been drained out of existence, and are now represented
mainly by seasonally wet meadowland. \Vhile there are a number of bonus areas
very few sites in the present class outside East Anglia merit grade 1 status in their
own right.
Natural sheets of water are extremely
scarce in the southern half of England, but
some river valleys outside East Anglia formerly had extensive flood-plain mires.
One of the most important remnants is on the extensive plain of the River Brue
draining to Bridgwater Bay in Somerset. Here, the large area known as the
Somerset Levels is a former complex of raised mire and flood-plain mire, now
largely cut away through long-continued removal of peat. Shapwick Heath (P.24)
contains remnants of both mire types which together merit grade 1 status. Just to
the south, the area of Sedgemoor is now mainly seasonally wet meadowland
drained by numerous dykes, but some parts remain swampy in a particularly wet
season. On the south side of Poole Harbour, Dorset, the grade 1 lagoon of Little
Sea (OW.21) has marginal reed-swamp which may be regarded as a bonus.
In south Wales, the coastal dune system
at Oxwich, Glamorgan, passes into a
hinterland of extensive reed-swamp and species-rich mesotrophic to eutrophic low
sward mire communities. This is the best known example of rich-fen in south Wales
and, together with the maritime interest, gives a site (P.32) of grade I quality. North
Wales has a number of mountain lakes and many tarns. Some of these are
interesting open water sites, but they generally have little fringing swamp. Certain
mesotrophic to eutrophic lowland lakes in Anglesey have a fairly good development
of marginal swamp, but none has been investigated from this angle, although Llyn
Coron is regarded as a grade 2 open water site. In Caernarvonshire, two flood-
plain mires, Cors Geirch in Lleyn and Ystumllvn near Criccieth, have been so
modified by drainage operations that they can no longer be regarded as nationally
important sites.
The meres of the west Midlands plain have
variable amounts of marginal swamp.
Of the grade 1 open water sites here, Sweat Mere, Shropshire, has well developed
fringing mire vegetation which represents a bonus, but Rostherne Mere, Cheshire,
has relatively little.
In northern England, the grade 1 open
water site of Hornsea Mere in Holderness,
east Yorkshire has fringing mire worthy of mention as a bonus and, in the Vale of
York, Skipwith Common has been given grade 1 status for its combination of dry
heathland, colonising birchwood and patches of flood-plain mire (cf. Cavenham-
Tuddenham Heath). Within the Malham-ArnclifFe grade 1 upland site in the Craven
Pennines, Yorkshire, Malham Tarn has an associated eutrophic fen (P.52, gr. 1) of
northern character which merits this status in its own right, and adds to the
astonishing diversity of wetland types in the Malham complex. Sunbiggin Tarn Fen
(P.53) within the Orton Fells grade i upland site has marginal calcareous swamp
which forms part of the wetland complex at this site, including additionally open
water and soligenous mire. On the edge of Morecambe Bay, Lancashire, the
artificially flooded valley known as Leighton Moss in Silverdale is an important
outlying northern reed-swamp with some of the characteristic breeding birds of the
Norfolk Broads. This is a grade 1 site (P.51) adjoining the limestone complex which
includes the grade i open water of Haweswater (with its marginal swamp providing
bonus interest).
The Lake District has by far the largest
sheets of open water in Britain outside
Scotland, but these are mainly oligotrophic mountain lakes in character, with steep,
hard and often rocky edges which do not favour the development of marginal
swamp. There are some fringing fens and carrs around the edges of Derwentwater
and Bassenthwaite Water (e.g. The Ings-see W.I33) but the best examples are
around some of the smaller lakes, notably Esthwaite Water and the adjoining Priest
Pot. Here, the existing North Fen NNR is a tiny but high quality area of mesotrophic
fen which rates as a bonus area within the Esthwaite Water grade i open water site.
In the same area, Blelham Bog NNR is a poor-fen developed over a kettle-hole on
one side of Blelham Tarn, but its vegetation is of too limited value to merit more
than grade 3. Again the tarn itself is of grade i status and so it is appropriate to
regard the NNR as a bonus area. In addition it has considerable value as a site for
Quaternary studies.
Scotland has numerous lakes of all sizes,
many of which (especially in the lowlands)
show development of marginal swamp. These are, however, the least studied of all
peatland types during the review, and much further survey remains to be done.
Many of the open waters rated as nationally important have marginal fen likely to be
worth including in the bonus category. This is particularly true of the base-rich
examples which occur widely in Galloway and the central Lowlands, and thence
through the eastern plains from east Perthshire to Aberdeenshire. Rich water sites
where the surrounding mire is regarded as at least grade 3 in value in its own right
include Black Loch, Kilconquhar Loch (OW.yg, gr. 2) and Lindores Loch, Fife;
Duddingston Loch, Midlothian; Carlingwark Loch, Kirkcudbrightshire; Loch
Rescobie (OW.Si, gr. 2), Angus; Lochs Clunie and Lowes, Perthshire; and Loch
Avich, Argyll. The machair swamps at Loch Hallan, South Uist, and Balranald, North
Uist, belong to the eutrophic class of mires vegetationally but are treated under
coastlands (Chapter 4). Many northern poor-fens remain to be investigated, but
here floristic variation is more limited, and it may well be that existing key sites are
adequately representative of this class of mires. Adjoining the south end of Loch
Lomond, on either side of the Endrick mouth are freshwater marshes and a
eutrophic flood-plain rnire, Aber Bogs (P.73), which has affinities with both northern
and southern types; this complex is identified as grade i within the Loch Lomond
composite grade 1 site. In Galloway, the neutral grassland grade 1 site known as
the Ken-Dee marshes passes into mesotrophic fen fringing the edge of this long,
open water system, and there is thus a bonus peatland interest here.
The eastern Highlands have the distinction
of possessing the largest flood-plain
mire in Britain outside the Norfolk Broads. The Insh Fens (P.87, gr. 1*) between
Kingussie and Loch Insh cover an area of almost 780 ha in the middle Spey Valley,
Inverness-shire. This great expanse of mire was once partly drained but has been
rejuvenated by the construction of a railway embankment on one side and artificial
banks to the River Spey. The vegetation is predominantly the characteristic
northern poor-fen contrasting with the eutrophic types of the Broads, and there is a
rich avifauna with a distinctly northern element. Loch Insh itself rates as a grade 1
open water site, and within the fens are small tarns and flooded oxbows. Altogether
this is one of the most important peatland sites in the country. The previously-
mentioned grade i ecosystem complex known as the Moor of Dinnet (P.88) on
Deeside includes two large tarns, Lochs Davan and Kinord (OW.76), with fringing
oligotrophic swamp and acidic Sphagnum mire grading into poor-fen and valley
mire.
North of the Great Glen, the lower reach
of the River Fleet in east Sutherland has
developed a large area of flood-plain mire and alder—willow carr after it was
disconnected from the sea by an estuarine embankment (the Mound) built in 1816.
The influence of the sea is still sufficient to give saline conditions just inside the
embankment and brackish effects for some distance upstream, but most of the
mire system is a mesotrophic fen. The Mound swamps represent a northern
counterpart to the Minsmere-
jWalberswick coastal flood-plain mires
in Suffolk (P.u), but [have had longer in
which to progress to carr. The area does not have the same degree of
ornithological interest as the Suffolk sites, and the carr woodland (grade 1) is more
important than the mire component, which is therefore regarded as a bonus.
Slightly farther south, the flood plain of the River Oykell between Sutherland and
Ross has a general appearance rather similar to that of the Spey at Insh Fens.
Incomplete survey suggests, however, that most of the Oykell site is better placed in
alluvial meadow and fresh-water marsh, though some parts may prove to be
sufficiently wet to rank as mire. The site is at present rated as a grade 2 neutral
grassland and described under these as it is inappropriate to attempt to grade the
various parts separately.
i Basin mires
This is a very local type of mire with
few examples in the southern half of England or
Wales. An area of eutrophic fen vegetation in Breckland, known as Cranberry
Rough, is best classified as basin mire since it has developed over and ; replaced
a small lake basin (Hockham Mere). It is regarded as a grade 2 site (P. 19).
An isolated basin mire in Radnor called
Llyn (P.33) has an undisturbed central
schwingmoor with open Sphagnetum ; and pine-grown margins, surrounded by
birch carr. This is rated grade 1* since it has the best representation of oceanic
mire vegetation found in any single basin mire and also has I a classical
stratigraphical sequence.
The most important examples of basin mire
are concen-i trated in three districts, all
in the northern half of England. The first district is the drift-covered Shropshire-
Cheshire plain in the Midlands, where some of the hollows containing basin mires
are probably of glacial origin, but others are believed to have been formed by
subsidence following solution and wastage of the underlying thick layers of rock salt
within the Triassic succession. The largest and in many ways most typical of these
Midland basin mires is Chartley Moss ! (P-42, gr. 1) in Staffordshire, where there is
a classical j schwingmoor or floating raft of Sphagnetum containing pools ; over a
considerable depth of open water in the basin. Characteristic colonisation by Scots
pine is well represented, and one area shows the influence of base-rich ground
water.
Clarepool Moss (P.43) near Ellesmere in
Shropshire is another partly pine-grown
basin mire with oligotrophic lawn communities, including a schwingmoor, but
compared with Chartley Moss has a more extensive development of mesotrophic
fen and carr, in association with a large open pool containing base-rich water. The
pool is one of the few examples of a small, deep and nutrient-rich open water body,
and for its combination of interests the site is given grade 1 status. A further stage
in the ecological series is represented by Wybunbury Moss (P.44, gr. 1) near
Crewe, Cheshire, where mesotrophic fen and carr occupy a large and increasing
proportion of the whole basin. The phenomenon of eutrophication is evident here,
and the Sphagnetum schwingmoor is only partly of a truly acidophilous type.
Wybunbury Moss is the most varied and
closely studied of British basin mires and
the data on stratigraphy, hydrology and floristics give a firm basis for evaluating
present and future changes. The inclusion of Sweat Mere and Crose Mere,
Shropshire, as an open water grade 1 site (OW-39) completes the main range of
ecological variation in the Midland basin mire series, for Sweat Mere has
peripheral zones consisting entirely of the hydroseral sequence from rich-fen
swamp to carr and damp mixed woodland. On their own, these fen communities
are perhaps not of first national importance, but they are appropriately included as
bonus areas.
The Abbots Moss (P.46) basin mire complex
in Cheshire is regarded as a grade 2
alternative to Chartley Moss, with predominantly acidophilous Sphagneta and a
high potential for hydrological research. Cranberry Bog (P.45) in Staffordshire has
a superb example of a rich fen lagg surrounding an acidophilous central Sphagnum
lawn, but is so small and vulnerable to marginal influence that it cannot rate higher
than grade 2.
The inclusion of a raised mire, Wem Moss
(P-40), gives a grade 1 series
adequately representative of the very varied complex of west Midlands mires.
The other two important districts for
basin mires in England are both in the far north,
on the coastal plain of Northumberland and in the lowlands of the Cumberland Plain
and low lying coastal strip south of St Bees. In Northumberland there are a number
of basin mires, ranging from oligotrophic to eutrophic, but only one, Newham Fen
(P.54) near Bamburgh, merits grade i status. This basin mire contains a fine
example of a vegetation type not represented in the Midlands series, namely, highly
calcareous fen with extensive 'brown moss' communities and their associated
vascular calcicoles. Such vegetation shows close parallels with that of calcareous
valley mires in the south, such as Cothill Fen, Berkshire, and Scarning Fen, Norfolk.
Much farther inland in Northumberland, Caw Lough (P.68) is a basin mire near the
Roman Wall, and has fragments of calcareous fen, but mainly a mixture of
oligotrophic to mesotrophic fen of a type well represented in many northern mires.
As this site seems to have no outstanding features, but is a good basin mire with a
wide range of vegetation, it is rated grade 2.
In Cumberland, the most important basin
mire is Moorthwaite Moss (P.56) east of
Carlisle, which appears to be the only example left of this mire type with a highly
acidophilous Sphagnetum. This site thus adds to the grade i series the opposite
vegetation extreme to Newham Fen. The Sphagnum hummock and hollow
communities are also an especially fine and actively growing example of
regeneration-complex mire surface. The peripheral belt of pinewood increases
rather than detracts from the range of vegetational interest. Farther south in
Cumberland, on the northern fringe of the Lake District, Tarn Moss (P.55) near
Trout-beck is an example of basin mire covered with a northern type of poor-fen
vegetation not represented in the other grade i basin mires so far described, and
merits this grade. It is more nearly allied in floristics to such sites as the Insh Fens
(flood-plain mire) and the valley mires of Rannoch Moor and Inverpolly.
Newton Reigny Moss (P.65) west of Penrith
is the only calcareous fen in
Cumberland. It is a western counterpart to Newham Fen for which it is a grade 2
alternative, but hydroseral development has progressed further, giving a greater
extent of carr and a lesser area of 'brown moss' carpets. Several characteristic rich-
fen species have declined or disappeared in recent years, and the site has tended
to dry out considerably. East of Penrith, another basin mire, Cliburn Moss (P.66) is
intermediate between Moorthwaite Moss and Newton Reigny Moss in ecological
character. It is a pine-grown poor-fen, with local development of meso-trophic
communities. The floristic combination is unusual but the site does not merit more
than grade 2. On the narrow plain fringing the south-west Cumberland coast are
several interesting but small basin mires. The largest of these is Hallsenna Moor
(P.67) near Drigg, a complex of acidic heathland, basin mire and carr. The mire is
largely poor-fen basically similar in type to that at Tarn Moss, Troutbeck, and though
there are certain floristic differences, these are not sufficient to warrant a grading
higher than 2.
In southern Scotland, the Whitlaw Mosses
(P-75) near Selkirk consist of four
separate though closely adjacent mires grading from valley to basin mire. The most
obvious basin mire in the group, Beanrig Moss, contains an unusual weakly
mesotrophic Sphagnetum different from the eutro-phic fen communities occupying
the other three sites. The whole group forms a grade 1 complex of very great
ecological interest. Adderstonlee Moss (P.74) also in Selkirkshire, has a varied
range of communities from the northern poor-fen type to calcareous fen. This
combination is unusual in the north and the site is considered to be sufficiently
different from any other mire to merit grade 1. Of the numerous other basin mires in
southern Scotland none of those examined is sufficiently different from the basin
mires already mentioned to be regarded as of first national importance. One
interesting though small site, Barmufflock Dam (P.81) in Renfrewshire, is another
particularly good example of mixed poor- and rich-fen, and merits grade 2 status.
In Aberdeenshire, Wartle Moss (P.92) has
been chosen as another grade 2
example of a northern mesotrophic basin mire. Basin mires occur in various other
parts of the Highlands and are associated with valley mires on Monadh Mor (P.100,
gr. 1) and in Abernethy Forest (P.93, gr. 2) but no further examples have yet been
seen that are sufficiently important or different from more southern basin mires to
warrant national status. Basin mires in this region tend to be obscured by the
general development of blanket mire, giving a continuous spread of peat over all
but steep ground.
Valley mires
Two regions, both in the lowlands of the
southern half of England, contain the best
examples of valley mire. The first stretches from Surrey, through the New Forest in
Hampshire, to Dorset, and has mainly oligotrophic valley mires associated with
acidic heathlands on base poor sands and gravels. The second, in Norfolk and
Suffolk, has mainly eutrophic types associated particularly with chalky boulder clay.
The national mire series should represent adequately the range of variation within
these two regions, and any distinctive geographical variants in other regions farther
north.
Of the numerous valley mires on the Greensand
of southeast England, the finest
example occurs on Thursley Common (P.2) in Surrey and has an exclusively
oligotrophic range of vegetation, set in an area of grade i heathland. Areas of valley
mire within the Ashdown Forest grade 1 heathland complex rate only as bonus.
The New Forest, rated as a whole as a
large grade i complex of woodland,
heathland and mire, is the most important single area in Britain for valley mires (P-
3), and the locus classicus for this mire type. These valley mires occupy shallow,
broad channels in a low plateau of Tertiary sandstones and clays capped by
gravels. They show a great range of variation, and especially good examples of
vegetational zonation parallel to the long axis, with the beginnings of mesotrophic
mire (sometimes with carr) along the central drainage track, and well-developed
undamaged Sphagnum lawns to each side. Cranesmoor is probably the finest
example of acidic valley mire in Britain, and has particular interest in its oceanic
flora and aligned pool system which links it with western and northern blanket mires.
The Denny Bog-White Moor complex contains several distinct valley mires with
central carr and oligotrophic schwingmoor showing gradation into wet heath.
Further variation is included in the Wilverley, Holmsley and Thorney Hill group,
which all form part of a single mire system. The first two sections have mesotrophic
centres, finely developed Sphagnum lawns and an especially rich flora, while the
Thorney Hill section is unusual for the area in being a calcareous fen, with
calcicolous 'brown mosses' and vascular plants. Hincheslea Bottom is regarded as
a good typical site for the area. These four systems are regarded as fully
representative of the very large range of diversity in the New Forest valley mires but
this large area contains a number of other examples.
In Dorset, Morden Bog (P.27) north-west
of Poole Harbour has a large valley mire
which forms an integral part of the grade i complex of dry and wet heathland partly
grown with Scots pine. The vegetation is rather different from that of the preceding
valley mires and has affinities with certain northern poor-fen communities, and the
insect fauna is outstanding. In the Isle of Purbeck, the once continuous but now
dissected area of acidic heathland has two grade 1* areas, Hartland Moor (L.88)
and Studland Heath (L.8g) which contain well-developed valley mires. The Hartland
mire rates as grade 1 in its own right (P.26) as it shows an interesting combination
of oligotrophic and mesotrophic communities, and has an outstandingly rich
invertebrate fauna. The valley mires of Studland Heath are more limited in diversity,
being mainly acidic, but they have considerable interest especially in their unusually
steep surface gradients and strongly patterned surfaces.
The contrasting calcareous valley mires
in Norfolk and north Suffolk occur mainly in
valley-head situations at the sources of certain rivers. Because of the national rarity
of calcareous mires of any type, three really high-quality examples in this district
have been rated as grade 1 although two of these are small in size. Seaming Fen
(P. 17) on the outskirts of East Dereham, and Smallburgh Fen (see Appendix) (P.
15) in the headwaters of one of the Broadland streams are the most outstanding in
their development of 'brown moss' carpets, though both have a range of other
eutrophic mire communities dominated by vascular plants, including carr, and a
remarkably rich flora for such small areas. At the head of the Waveney between
Thetford and Diss is a more extensive valley mire, Redgrave-South Lopham Fen
(P. 18) which has extensive areas of reed-swamp and other tall-herb, rich-fen
vegetation of a kind especially associated with East Anglian hydroseres. There is a
variety of communities ranging from lower herb swards to developing carr and the
area has a rich invertebrate fauna. Thel-netham and Bio' Norton Fens(P.21) at the
head of the Little Ouse to the west have examples of the ' brown moss '-herb
carpets and there is a luxuriant development of mixed tall herbaceous vegetation.
This site is sufficiently important to be rated grade 2 despite deterioration following
recent adjacent drainage improvement.
Roydon Common (P.i6) near King's Lynn
is different from the other Norfolk sites
described in that its valley mire occupies a shallow valley in an area of acidic
heathland (itself regarded as grade 1). As in some of the New Forest examples
there is a gradation from wet heath to calcareous fen and carr and the whole site is
of outstanding interest. Buxton Heath (P.22) nearer Norwich has a similar complex
of acidic heathland and calcareous fen, which could be regarded as a grade 2
alternative to Roydon Common. Dersingham Bog (P.23) north of King's Lynn, is
interesting as a completely acidic valley mire in the grade 2 heathland area of
Sandringham Warren. It has unusual surface features but is not regarded as of first
national importance. Interesting mixed valley mires with much Sphagnum also occur
as a bonus within the grade 2 acidic heathland site of Holt Lowes west of Cromer.
Elsewhere in the southern half of England,
Cothill Fen (P.4) near Oxford is a small
but very fine grade i example of calcareous valley mire on Jurassic limestone, and
has been much used as a research site. Greywell Fen (P.5) in north Hampshire is a
rather different type of eutrophic valley mire, but as its main features are
represented on other sites, grade 2 status is appropriate. On the south-western
granite moorlands of Dartmoor and Bodmin Moor a number of acidic mires bridge
the gap between valley and upland soligenous mire, but these are probably
adequately represented within the North Dartmoor upland and blanket mire grade 1
site, and key examples elsewhere in Devon or Cornwall have not been identified.
In south Wales, Rhos Goch, Radnor, is
important mainly as a raised mire, but
contains an example of somewhat acidic valley mire which is of interest as a bonus.
Cors Graianog (P.39) at the foot of the mountains of south Caernarvonshire and
Cors y Sarnau (P.38) in Merioneth, are more upland acidic valley mires of a type
represented elsewhere, but are both felt to be of grade 2 quality.
Anglesey in north Wales has some affinities
with East Anglia in its strong
representation of eutrophic fens and open waters. Most of the former are valley
mires, and two closely adjacent examples on Carboniferous Limestone, Cors Goch
(Anglesey) (P.36) and Cors Erddreiniog (P.35) are unusual in being western and
oceanic examples of calcareous mire, for most examples of this type are rather
eastern and continental. Also on Anglesey, Cors Bodeilio and Cors y Farl (P.37)
are regarded as an aggregate grade 2 alternative for the above two grade 1 sites.
Three grade 1 valley mires are recognised
in northern England. In the North Riding
of Yorkshire a deep glacial overflow channel in the North York Moors contains a
valley mire known as Fen Bogs (P.59) which has developed an ombrogenous
surface in places, and otherwise has poor-fen communities of a northern type. This
is an extreme topographic form of valley mire. In Northumberland the Muckle Moss
(P.58) near Haltwhistle is a particularly good example of a Sphagnum-dominated
schwingmoor and has especial floristic interest, though the communities are
entirely acidophilous. Cumwhitton Moss (P.57, gr. i) near Carlisle is important for its
highly unusual combination of ecological features, with variable colonisation of
mixed acidic and mesotrophic mire by birch and pine. It is a floristically rich site
giving an interesting contrast with the acidic basin mire of Moorthwaite Moss less
than a kilometre away. West of Carlisle, Biglands Bog (P.69) is a mesotrophic
valley mire in which the rich-fen is interrupted very strikingly by a small area of
ombrogenous Sphagnum surface having strong similarity to the adjacent raised
mires of the Solway. This is an important site, but recent deterioration through
sewage contamination of the ground water has reduced its scientific value, and it is
regarded as grade 2. The grade 1 woodland site of Roudsea Wood, Lancashire,
contains an interesting example of eutrophic valley mire.
In southern Scotland a small aggregate
group of four mires known as Whitlaw
Mosses (P.75) near Selkirk includes three eutrophic valley mires with a wide range
of vegetation from swamp to carr. There is a rich flora, with a strongly northern
element, and the group is regarded as the best example (grade 1) of northern rich
valley mire. Dunhog Moss (P.82) in the same district is a grade 2 example of
northern poor-fen of a widespread type. Heart Moss (P.83, gr. 2) in
Kirkcudbrightshire is a valley mire with a wide range of communities from
oligotrophic to mesotrophic, but is rather similar vegetationally to certain basin
mires.
In the Highlands, valley mires occur widely,
but in uplands are largely replaced by
types regarded as soligenous mires, on ground with more definite slope. On
Rannoch Moor (P.85), an important area of blanket mire on the borders of
Perthshire and Argyll, are numerous examples of mire affected by ground water
seepage and many of these could be regarded either as valley or soligenous
mires. Their vegetation is of a northern poor-fen type and grades into blanket mire
or into swamp fringing the numerous tarns. The area selected as grade 1* for its
blanket mires contains valley mires which are of similar quality in their own right.
The important grade i complex of open water, mire moorland and woodland known
as the Moor of Dinnet, to the east of the Cairngorms in Aberdeenshire, has good
examples of northern valley mires (P.88) with poor-fen (Black Moss and Ordie
Moss) in a much more continental area. In Abernethy Forest (W. 187(6), gr. 1) in the
Cairngorm foothills of Invernessshire, a grade 2 complex of valley and basin mires
(P.93) gives a wide range of vegetation types, from strongly acidophilous to weakly
meso-philous, and forms an interesting (though smaller) northern counterpart to the
New Forest valley mires. The Kinrara section of the Aviemore birchwoods grade I
site contains a good bonus example of oligotrophic valley mire with northern poor-
fen resembling that of the Loch Insh Fens. In the Black Isle of east Ross, the area of
glacial deposition known as the Monadh Mor (P.100), has a complex of pinewood
on dry ridges and hillocks with acidic valley mires and lochans in channels and
hollows. Northern poor-fen is well represented and the complex has Scandinavian
affinities. There are similarities to the Abernethy Forest mires, but this system is
regarded as more important and rated as grade I. Elsewhere in the Highlands,
valley mires are particularly well developed in the coastal belt of Lewisian Gneiss. A
very fine example lies immediately west of Loch Sionascaig within the present
Inverpolly NNR (Inverpolly Valley Mire, P. 101, gr. 1). This has an oceanic mixed
mire vegetation including northern poor-fen and well-developed Sphagnum
hummocks which grade laterally into marginal blanket mire. Another example of this
type at Little Loch Roag on Lewis (P. 107) is included as a grade 2 alternative.
Soligenous mires
Soligenous (flush) mires are represented
in virtually all the upland grade 1 and 2
sites and are described under these as it is inappropriate to attempt to grade them
separately.
There follows a list of the upland sites
which contain the more noteworthy examples
of soligenous mire.
Oligotrophic soligenous mires
These are especially widespread and occur
within the majority of upland sites
listed, but the following are the notable examples:
North Dartmoor, Devonshire; Rhinog, Merioneth;
Eryri, Caernarvonshire; Moor
House and Cross Fell, Westmorland-Cumberland; Mallerstang—Swaledale Head,
Westmorland-Yorkshire; Cairnsmore of Fleet, Kirkcudbrightshire; Caenlochan-
Clova, Angus; Cairngorms, Inverness-shire-Aberdeenshire-Banffshire; Rhum,
Inverness-shire; Beinn Dearg and Seana Bhraigh, Ross; Ben Wyvis, Ross;
Foinaven and Meall Horn, Sutherland; Inverpolly, Ross. Rannoch Moor, Perthshire,
is a grade i blanket mire and soligenous mire site.
Mesotrophic and eutrophic soligenous mires
These are much more local and do not occur
on all upland key sites. Their
distribution depends on the occurrence of strongly calcareous rock and soils, so
they are best developed on the Carboniferous Limestone of northern England,
Dalradian limestone and calcareous schist in the eastern Highlands, and dolomitic
Durness Limestone in the western Highlands. The following are notable examples
within grade 1 upland sites.
Malham-Arncliffe, Yorkshire; Orton Fells,
Westmorland; Moor House and Cross
Fell, Westmorland-Cumberland; Upper Teesdale, Durham-Yorkshire; Ben Lawers-
Meall nan Tarmachan, Perthshire; Caenlochan-Clova, Angus; Tulach Hill,
Perthshire; Morrone, Aberdeenshire; Rhum, Inverness-shire; Strath Suardal, Skye,
Inverness-shire; Inchnadamph, Sutherland; Durness, Sutherland; Invernaver,
Sutherland.
