Synonymy

Juniperus-Arctostaphylos sociation Poore & McVean 1957; Juniperetum nanae McVean & Ratcliffe 1962 p.p.; Juniperus nana nodum Birks 1975 p.p.

Constant species

Calluna vulgaris, Deschampsia flexuosa, Erica cinerea, Juniperus communis ssp. nana, Potentilla erecta, Scirpus cespitosus, Hypnum cupressiforme s.l., Racomitrium lanuginosum, Pleurozia purpurea, Cladonia uncialis.

Rare species

Arctostaphylos alpinus, A. uva-ursi, Loiseleuriaprocumbens, Herbertus borealis, H. stramineus, Plagiochila carringtonii.

Physiognomy

Prostrate juniper referable to Juniperus communis ssp. nana occurs as an occasional, sometimes with modest local abundance, in a variety of dwarfed sub-shrub heaths in Britain, notably in the Calluna-Racomitrium and Calluna-A. alpinus types. But in the Calluna-Juniperus heath, it is more or less consistently dominant in the sub-shrub mat and accompanied by a small but distinctive element of oceanic hepatics.

The mat is generally less than 10 cm thick and often severely wind-pruned to much less than this, fairly continuous in the best developed stands, though more fragmentary over erosion surfaces and where there has been burning, to which the dwarf juniper is very sensitive (McVean 196\b, Poore & McVean 1957). A number of other sub-shrubs are well represented, with Calluna vulgaris and Erica cinerea being especially frequent, and the former often fairly abundant, though not generally assuming dominance. Arctostaphylos uva-ursi and A. alpinus are somewhat less common and usually of low cover and Empetrum nigrum spp. hermaphroditum occurs occasionally. Vaccinium myrtillus and V. uliginosum are scarce and the community provides an occasional locus for Loiseleuria procumbens.

Vascular associates are typically rather few in number and occur as scattered and often stunted individuals among the mat. Deschampsia flexuosa, Scirpus cespitosus and Potentilla erecta are constant, with Huperzia selago, Solidago virgaurea (in its so-called var. cambrica), Dactylorhiza maculata, Polygala serpyllifolia, Succisa pratensis and Antennaria dioica more occasional. Carex panicea, C. pilulifera, C. bigelowii, Festuca vivipara and Nardus stricta can also sometimes be found and, more unusually, there can be some Thymus praecox.

In some stands, the cryptogam flora seems little different from other kinds of dwarfed sub-shrub heath, as in some of the semi-degraded samples of Poore & McVean (1957) and of McVean & Ratcliffe's (1962) lichenosum and, indeed, such vegetation where the juniper cover is lower than usual is best shifted into other communities.

Synonymy

Carex saxatilis sociation Poore 1955Z?; Carex saxatilis mire McVean & Ratcliffe 1962: Calliergono sarmentosi-Caricetum saxatilis Dierssen 1982.

Constant species

Carex demissa, C. saxatilis, Eriophorum angustifolium, Polygonum viviparum, Thalictrum alpinum, Aneura pinguis, Drepanocladus revolvens, Hylocomium splendens, Scapania undulata.

Rare species

Alchemilla filicaulis ssp. filicaulis, Carex atrofusca, C. microglochin, C. saxatilis, C. vaginata, Juncus biglumis, J. castaneus, Kobresia simpliciuscula.

Physiognomy

Carex saxatilis occurs at low frequency in a variety of wetter vegetation types at high altitudes but here it is typically dominant in a kind of montane mire which has a distinctive assemblage of associates. The sward is generally low, less than 20 cm tall, and often rather open with patchy exposures of soil. Sedges as a group figure quite prominently: apart from C. saxatilis, C. demissa, C. echinata and C. nigra are very frequent and each can be abundant and C. dioica and C. pulicaris also occur occasionally. Such species provide considerable continuity with other more calcicolous mires like the Pinguiculo-Caricetum and lower-altitude stands of the Carici-Saxifragetum but, in contrast to those communities, C. panicea is very scarce here and C. bigelowii is fairly consistent, particularly in grassier transitions to the surrounding swards. As in high-altitude stands of the Carici-Saxifragetum, open stony patches in the vegetation provide a niche for the very rare Arctic-Alpine sedges, C. atrofusca and C. microglochin. C. vaginata has also been recorded in this community.

Apart from Eriophorum angustifolium, a frequent species here which can attain covers of over 10%, almost all the other herbs occur as sparse, scattered individuals. Selaginella selaginoides and Pinguicula vulgaris, both of which are very common, emphasise general similarities with our other calcicolous flushes, but more characteristic are the Arctic-Alpines Thalictrum alpinum, Polygonum viviparum and Juncus triglumis. All these can occur in more montane stands of the Carici-Saxifragetum, together with Saxifraga oppositifolia and S. stellaris, which are scarce to occasional here, but S. aizoides itself is not frequent in the Caricetum saxatilis and, when it does occur, it is typically of low cover. Also rather distinctive is the presence of certain poor-fen herbs like Viola palustris, Caltha palustris and Agrostis canina ssp. canina. Other vascular species recorded occasionally include Leontodon autumnalis, Euphrasia officinalis agg. (including E. scotticd), Geum rivale, Huperzia selago, Ranunculus acris, Rumex acetosa, Alchemilla glabra and the rare A. filicaulis ssp. filicaulis.

Synonymy

Vaccinietum myrtilli Smith 1900, Lewis & Moss 1911, Tansley 1939, Fidler et al. 1971; Vaccinium-xïàgQ & Kzccmzwm-summit Smith & Moss 1903, Smith & Rankin 1903; Gr amino-Vaccine turn Smith 1911b; Vaccinium-edge Moss 1913; Empetreto-Vaccinetum Burges 1951 p.p.; Lichen-rich Vaccinium-Festuca association Poore 19556; Vaccinium-Chamaepericlymenum nodum Poore & McVean 1957 p.p.; Vaccineto-Empetretum McVean & Ratcliffe 1962; Festuceto-Vaccinetum McVean & Ratcliffe 1962, Evans et al. 1977, Ferreira 1978; Festuca ovinaiDeschampsia flexuosa grassland King 1962 p.p.; Vaccinium myrtillus- heath moss sociation Edgell 1969; Mountain Vaccinium heaths Gimingham 1972p.p.; Phyllodoce caerulea sites Coker & Coker 1973 p.p.; Huperzio-Vaccinetum Hill & Evans 1978; Rhytidiadelphus loreus-Vaccinium myrtillus community Birse 1980.

Constant species

Deschampsia flexuosa, Galium saxatile, Vaccinium myrtillus, Dicranum scoparium, Pleurozium schreberi.

Rare species

Loiseleuria procumbens, Minuartia sedoides, Phyllodoce caerulea, Salix lapponum, Barbilophozia lycopodiodes, Scapania ornithopodiodes.

Physiognomy

The Vaccinium myrtillus-Deschampsia flexuosa heath includes a variety of moss-rich and grassy sub-shrub vegetation in which Vaccinium myrtillus is the most frequent and generally the most abundant ericoid, with Calluna vulgaris typically having a rather inconspicuous role: heather is usually only occasional here and present as scattered plants that are often noticeably lacking in vigour. V. myrtillus is not always truly dominant, however, and other sub-shrubs sometimes make a sizeable contribution to the canopy, which is generally 1-2 dm tall, occasionally rather open and, even where extensive, is without that uniform density of growth found in heaths with much young Calluna. Most frequent among the associated sub-shrubs is Empetrum nigrum, usually ssp. hermaphroditum where it has been possible to distinguish the taxa, though sometimes clearly ssp. nigrum, and occasionally both plants growing together. Typically, the procumbent stems of the crowberry penetrate quite far among the bilberry, branching out into patches which can be locally abundant. Some of the vegetation subsumed here has co-dominant E. nigrum as in the various kinds of Vaccinio-Empetretum described by Burges (1951) and McVean & Ratcliffe (1962), and, of course, being evergreen, the crowberry catches the eye more than the deciduous bilberry in stands without a covering of winter snow.

V. vitis-idaea is about as common as E. nigrum, though typically much less abundant. V. uliginosum, on the other hand, is rather scarce and preferential for one sub-community but it can have locally high cover there, even attaining co-dominance in some stands (Poore & McVean 1957,

Synonymy

Erica vagans-Schoenus nigricans ‘Tall Heath’ Coombe & Frost 1956a; Erica vagans heath Gimingham 1972 p.p.; Ulici gallii-Ericetum vagantis Bridgewater 1970 p.p.; Ulicimaritimi-Ericetum vagantis (Géhu 1962) Géhu & Géhu 1973 emend. Bridgewater 1980; Erica vagans-Schoenus nigricans heath Hopkins 1983 p.p.

Constant species

Anagallis tenella, Carex pulicaris, Erica tetralix, E. vagans, Festuca ovina, Molinia caerulea, Potentilla erecta, Schoenus nigricans, Serratula tinctoria, Succisa pratensis, Ulex gallii, Campylium stellatum.

Rare species

Agrostis curtisii, Erica vagans, Scilla verna.

Physiognomy

The Erica vagans-Schoenus nigricans heath is one of the two sub-shrub communities to which the nationally-rare Oceanic West European Erica vagans makes a constant and often prominent contribution, its long spikes of flowers adding a distinctive pale pink to the splash of colour provided by the ericoids in July through to September. Often, however, it is the consistent presence of Schoenus nigricans which marks out stands of this vegetation, its tall greyish semi-evergreen foliage standing a little proud of the rest of the cover (hence Coombe & Frost's (1956a) epithet ‘Tall Heath’). In fact, Schoenus can be found as a rare associate in wetter tracts of various lowland heath types, but here it is an invariable member of the community and one of the most important structural components of the vegetation, occurring, often in abundance and generally in a strongly-tussocky form, with dense caespitose clusters of shoots growing on bulky rootstocks (Sparling 1962a, 1968, Wheeler 1975). Molinia caerulea, too, which is also constant and frequently of high cover, typically occurs as pronounced tussocks and E. vagans, together with the next most common sub-shrub, E. tetralix, often forms compact bushes. Thus, although these four species generally dominate in intimate mixtures, forming a canopy 2-4 dm tall, there is often beneath this a well-defined system of runnels between the individual plants. These are flooded to a depth of a few centimetres for long periods during the winter and, more briefly, throughout the year after heavy rain, and so can provide a microhabitat different in character from the sides and tops of the Schoenus and Molinia tussocks, which are far removed from the influence of the ground waters.

The background to the work

It is a tribute to the insight of our early ecologists that we can still return with profit to Types of British Vegetation which Tansley (1911) edited for the British Vegetation Committee as the first coordinated attempt to recognise and describe different kinds of plant community in this country. The contributors there wrote practically all they knew and a good deal that they guessed, as Tansley himself put it, but they were, on their own admission, far from comprehensive in their coverage. It was to provide this greater breadth, and much more detailed description of the structure and development of plant communities, that Tansley (1939) drew together the wealth of subsequent work in The British Islands and their Vegetation, and there must be few ecologists of the generations following who have not been inspired and challenged by the vision of this magisterial book.

Yet, partly because of its greater scope and the uneven understanding of different kinds of vegetation at the time, this is a less systematic work than Types in some respects: its narrative thread of explication is authoritative and engaging, but it lacks the light-handed framework of classification which made the earlier volume so very attractive, and within which the plant communities might be related one to another, and to the environmental variables which influence their composition and distribution. Indeed, for the most part, there is a rather self-conscious avoidance of the kind of rigorous taxonomy of vegetation types that had been developing for some time elsewhere in Europe, particularly under the leadership of Braun-Blanquet (1928) and Tüxen (1937). The difference in the scientific temperament of British ecologists that this reflected, their interest in how vegetation works, rather than in exactly what distinguishes plant communities from one another, though refreshing in itself, has been a lasting hindrance to the emergence in this country of any consensus as to how vegetation ought to be described, and whether it ought to be classified at all.

In fact, an impressive demonstration of the value of the traditional phytosociological approach to the description of plant communities in the British Isles was published in German after an international excursion to Ireland in 1949 (Braun-Blanquet & Tüxen 1952), but more immediately productive was a critical test of the techniques among a range of Scottish mountain vegetation by Poore (1955a, b, c).

Synonymy

Empetreto-Vaccinetum Burges 1951 p.p.; Vaccinium myrtillus-hchen heath Poore & McVean 1957; Empetrum-Xwhzn heath Poore & McVean 1957; Cladineto-Vaccinetum McVean & Ratcliffe 1962; Festuceto-Vaccinetum rhacomitrosum McVean & Ratcliffe 1962p.p.; Vaccinium myrtillus-Empetrum hermaphroditum nodum Huntley 1979; Festuceto-Rhacomitrietum lanuginosi (Birse & Robertson 1976) Birse 1980 p.p.; Carex bigelowii-Festuca vivipara Association (Birse & Robertson 1976) Birse 1980 p.p.

Constant species

Carex bigelowii, Deschampsia flexuosa, Vaccinium myrtillus, V. vitis-idaea, Racomitrium lanuginosum, Cetraria islandica, Cladonia arbuscula, C. uncialis.

Rare species

Loiseleuria procumbens, Kiaeria starkei.

Physiognomy

Like its heather-dominated counterpart, the Vaccinium myrtillus-Cladonia arbuscula heath consists essentially of a very low mat of sub-shrubs with an abundance of lichens, which again often mark out stands from a distance with a yellowish or grey-green tinge. Indeed, if anything, the lichens tend to be more extensive throughout this vegetation, and their dominance over the other components is more frequent and more extreme than in the Calluna-Cladonia heath. And, among the subshrubs, Calluna itself is uncommon overall: it increases in frequency in one sub-community but it is typically of low cover even there and of little structural importance, so the kind of wind-waved canopy associated with an abundance of flattened heather bushes is not usual here. The mat is still, however, very short, usually only 5-10 cm thick, but it is Vaccinium myrtillus that provides its most consistent element and, although this becomes sparse and noticeably lacking in vigour in more exposed situations, it is quite often abundant and a fairly regular co-dominant in what can be a dense and springy cover. V. vitis-idaea is somewhat less common and generally not so extensive and, in certain kinds of Vaccinium-Cladonia heath, it becomes distinctly patchy. V. uliginosum very occasionally shows local prominence, but overall it is scarce.

The other important sub-shrub in the community is Empetrum nigrum, almost always ssp. hermaphroditum and, in some of the vegetation included here (what McVean & Ratcliffe (1962) recognised as Cladineto-Vaccinetum), it becomes very frequent and often rivals or exceeds the Vaccinia in its cover. Alchemilla alpina can also be found, but it is nothing like so common or abundant as among the grassier stands of the Vaccinium-Deschampsia heath. The rare Arctic-Alpine Loiseleuria procumbens is very occasionally recorded, although neither it, nor the Arctostaphylos spp., play the sort of role here that they have in the Calluna-Cladonia or Calluna-A. alpinus heaths.

Synonymy

Scirpetum cespitosi Watson 1932, Fraser 1933, Tansley 1939 p.p.; Trichophoreto-Eriophoretum typicum McVean & Ratcliffe 1962, Birks 1973, Evans et al. 1977; Juncus squarrosus bog McVean & Ratcliffe 1962 p.p.; Pleur ozia purpurea-Erica tetralix Association Br.-Bl. & Tx. 1952 sensu Moore 1968 p.p.; Eriophorum vaginatum bog, low-level facies Edgell 1969; Blanket bog Ward et al. 1972; Mire nodum 12 Daniels 1978; Calluno-Molinietum’. Hill & Evans 1978 p.p.; Vaccinio-Eriophoretum Hill & Evans 1978 p.p.; Erico-Sphagnetum papillosi Moore (1964) 1968 emend. Birse 1980 p.p.; Erica tetralix-Sphagnum papillosum mire Ratcliffe & Hattey 1982 p.p.; Pleurozio-Ericetum tetralicis Dierssen 1982 p.p.; Virgin peatland l.ii & l.iii Hulme & Blyth 1984; Disturbed peatland 3.iv Hulme & Blyth 1984.

Constant species

Calluna vulgaris, Erica tetralix, Eriophorum angustifolium, E. vaginatum, Molinia caerulea, Narthecium ossifragum, Potentilla erecta, Scirpus cespitosus, Sphagnum capillifolium, S. papillosum.

Rare species

Campylopus atrovirens var. falcatus, C. setifolius, C. shawii, Sphagnum imbricatum, S. strie turn.

Physiognomy

The Scirpus cespitosus-Eriophorum vaginatum mire is a blanket bog community dominated by mixtures of monocotyledons, ericoid sub-shrubs and Sphagna, the two former groups of plants usually giving the vegetation its distinctive character when it is seen from a distance, but the last often occupying more of the ground, at least in wetter stands. The community can occur as extensive, fairly uniform tracts in which there is a fine-grained alternation of dominance among the species in these different elements from place to place; or, on mires with strong surface undulations, it can comprise the hummock component, with the plants showing a more obvious zonation in relation to the height of the water-table and the vegetation giving way in the hollows to Rhynchosporion pools.

Among the bulkier vascular species, the most common are Scirpus cespitosus, Eriophorum vaginatum, Molinia caerulea, Calluna vulgaris and Erica tetralix, mixtures of which form an uneven-topped tier, 2-3 dm tall and often rather open. The high frequency of E. vaginatum is one of the features which helps distinguish this vegetation from the most closely-related kind of wet heath, the Scirpus-Erica community, with which it is often associated; though, in fact, E. vaginatum is rarely very abundant here and never a consistent co-dominant, as it is in most types of Calluna-Eriophorum mire.

Synonymy

Carex rostrata-Sphagnum warnstorfianum nodum McVean & Ratcliffe 1962, Eddy et al. 1969; Violo-Epilobietum sphagnetosum recurvae Jones 1973 p.p.; Menyantho-Sphagnetum teretis Dierssen 1982. Constant species

Carex nigra, C. rostrata, Epilobium palustre, Festuca ovina, Potentilla erecta, Selaginella selaginoides, Viola palustris, Aulacomnium palustre, Calliergon cuspidatum, Hylocomium splendens, Rhizomnium pseudopunctatum, Sphagnum teres, S. warnstorfii.

Rare species

Homalothecium nitens, Sphagnum subsecundum.

Physiognomy

The Carex rostrata-Sphagnum warnstorfii mire has a dominant cover of sedges over an extensive carpet of base-tolerant Sphagna and a fairly numerous and diverse assemblage of herbs. As in the lowland counterpart of this community, the Carex-Sphagnum squarrosum mire, Carex rostrata and C. nigra are the commonest sedges, the former generally the more abundant and often of high cover, the latter usually subordinate though locally dominant. Other poor-fen sedges, C. panicea, C. echinata and C. demissa, occur frequently and sometimes in abundance, and C. pulicaris is occasional, but the more calciolous C. dioica is rare and C. curta, an occasional associate of C. rostrata in oligotrophic mires, likewise scarce. There is frequently a little Eriophorum angustifolium among the sedge cover, much less often small amounts of one of the bulkier Junci, Juncus articulatus or, more rarely, J. effusus or J. acutiflorus.

The Sphagnum carpet is typically extensive and quite distinctive in the prominence, along with S. recurvum, of the base-tolerant S. teres and S. warnstorfii, the latter an especially good preferential for this kind of montane mire. S’, subsecundum sensu stricto occurs more occasionally but is also very characteristic and the community provides one of the loci in Britain for S. contortum, though it is not so common here as in the Carex-Calliergon mire. S. squarrosum occurs occasionally but is not so consistent as in the Car ex-Sphagnum squarrosum mire. Other low-frequency species include S. palustre, S. girgensohnii, S. capillifolium, S. subnitens and S. papillosum, all generally of low cover. S. cuspidatum and S. auriculatum are typically absent.

Other bryophytes are numerous with Aulacomnium palustre and Rhizomnium pseudopunctatum attaining higher frequency here than in any other of our montane mires. Also distinctive are Calliergon cuspidatum, C. stramineum and, less frequently, the montane C. sarmentosum, though not C. trifarium which is more typical of the Caricetum saxatilis.

Synonymy

Sphagnetum Rankin 1911b p.p.; Sphagnetum regeneration complex Tansley 1939 p.p.; Scheuchzeria palustris vegetation Sledge 1949; Drosera intermedia-Schoenus nigricans Gesellschaft Braun-Blanquet & Tüxen 1952 p.p.; Sphagnum Hummock Complex, Sphagnum cuspidatum & S. pulchrum phases Rose 1953; Pool & furrow communities Pearsall 1956; Pool communities Ratcliffe & Walker 1958, Boatman & Armstrong 1968, Moore 1977, Boatman et al. 1981; Rhynchospora-Sphagnum vegetation Newbould 1960; Trichophoreto-Eriophoretum pool component McVean & Ratcliffe 1962; Eriophorum angustifolium-Sphagnum cuspidatum Association Birks 1973; Rhynchosporetum albae Koch 1926 sensu Birse 1980 p.p.; Caricetum limosae Dierssen 1982 p.p., Osvald 1923 ememZDierssen 1978 sensu Birse 1984p.p;,Pool communities 2.ii & 2.iii Hulme & Blythe 1984; Peatland noda 13-20 Lindsay et al. 1984; Sphagnum lawn bog hollows NCC New Forest Bogs Report 1984.

Constant species

Eriophorum angustifolium, Menyanthes trifoliata, Sphagnum auriculatum, S. cuspidatum.

Rare species

Hammarbya paludosa, Rhynchospora fusca, Scheuchzeria palustris, Utricularia intermedia, Sphagnum pulchrum.

Physiognomy

The Sphagnum auriculatum bog pool community typically consists of floating masses or soft wet carpets of Sphagna with scattered vascular plants growing on or through them or in areas of open water between. The dominant Sphagna are S. auriculatum (including var. inundatum, sometimes considered within S. subsecundum) and S. cuspidatum’. the constancy and general abundance of the former, together with the rarity here of S. recurvum, provide a good contrast with the closelyrelated Sphagnum cuspidatum!recurvum bog pools.

Locally, throughout the range of the community, the bright orange-yellow S. pulchrum provides a conspicuous enrichment of this element of the vegetation, growing semi-submerged with the other species (as on Brishie bog, the only one of the Silver Flowe mires in Dumfries and Galloway where Ratcliffe & Walker (1958) found it) or as a somewhat firmer mat upon them (as on some of the lowland English valley mires described by Rose (1953) who distinguished a separate S. pulchrum phase).

Synonymy

Arctostaphylos mat Crampton 1911; Loiseleuria-Arctous sociation Poore & McVean 1957; Arctoeto-Callunetum McVean & Ratcliffe 1962, Prentice & Prentice 1975; Alectorio-Callunetum vulgaris (Birse & Robertson 1976) Birse 1980p.p.; Vaccinio-Ericetum cinereae (Birse & Robertson 1976) Birse 1980 p.p.

Constant species

Arctostaphylos alpinus, Calluna vulgaris, Deschampsia flexuosa, Huperzia selago, Racomitrium lanuginosum, Cladonia arbuscula, C. uncialis.

Rare species

Arctostaphylos alpinus, A. uva-ursi, Loiseleuriaprocumbens, Cetraria norvegica.

Physiognomy

Arctostaphylos alpinus occurs with some frequency and occasionally with local abundance in various kinds of dwarfed sub-shrub vegetation, but, through the heart of its range, it is most typical of this Calluna vulgaris-A. alpinus heath where it is a constant, though generally a subordinate one, in the woody mat. Characteristically here, this is very low, almost always less than a decimetre thick, sometimes just a couple of centimetres and often discontinuous with stretches of bare stones between. It is usually dominated by Calluna, the bushes stunted or flattened in the direction of the wind, with the muchcontorted branches finely interlocked. A. alpinus almost always contributes less than 25% of the cover of the mat, but its prostrate stems can grow beneath the heather and they put up little branched sprigs with rather striking bright green reticulate leaves. A. uva-ursi, of generally similar growth habit though with evergreen foliage, also occurs very occasionally in small amounts.

One or other of the crowberries is also very frequent, though of only low to moderate cover, with the creeping stems ramifying among the mat: Empetrum nigrum ssp. hermaphroditum is strongly preferential to the higher altitudes from which this kind of vegetation was first described, and ssp. nigrum largely confined to lower situations. Loiseleuria procumbens, another creeping evergreen Arctic-Alpine, is also characteristically found with ssp. hermaphroditum here, the Calluna-A. alpinus heath providing its major locus in the western part of its range. Erica cinerea, on the other hand, is a frequent companion of ssp. nigrum in lower-altitude stands of the community.

Vaccinium myrtillus occurs commonly throughout, but typically as sparse shoots, and V. uliginosum and V. vitis-idaea are only very occasionally found. Salix herbacea is sometimes seen as small scattered sprigs. Juniperus communis ssp. nana occurs in some stands, but the generally small contribution of this plant here helps distinguish this vegetation from the Calluna-Juniperus heath.

Synonymy

Molinietum caeruleae Moss 1911, Rankin 1911a, b, Smith 1911, Crampton 1911, Stapledon 1914, Jefferies 1915, Fraser 1933, Tansley 1939, ail p.p.; Molinia-Myrica nodum McVean & Ratcliffe 1962, Adam et al. 1977; Molinia caerulea grassland McVean & Ratcliffe 1962, Edgell 1969, Meek 1976, Meade 1981 p.p.; Junco acutiflori-Molinietum O’Sullivan 1968, Hill & Evans 1978, Ratcliffe & Hattey 1982 p.p.; Festuco-Molinietum anthoxanthosum Evans et al. 1977; Molinia flushes Ferreira 1978; Wet Grassy Juncus Heath NCC Devon Heathland Report 1980; Myricetum galis Birse 1980; Molinia caerulea-Myrica gale community Wheeler 1980c p.p.; Molinia-Potentilla erecta nodum Bignal & Curtis 1981; Erica vagans-Schoenus nigricans heath Hopkins 1983 p.p.

Constant species

Molinia caerulea, Potentilla erecta.

Rare species

Agrostis curtisii, Erica vagans, Lobelia urens.

Physiognomy

The Molinia caerulea-Potentilla erecta mire encompasses vegetation of quite widely differing floristics and physiognomy, but characterised throughout by the overwhelming abundance of Molinia. This is a feature which helps distinguish the community from rather similar vegetation types of the Juncion acutiflori and Caricion nigrae, where Molinia can occur occasionally but where dominance is usually held by rushes or small sedges, themselves quite frequent here, though typically of subsidiary cover. monlinia-dominance is not, however, confined to this community in western Britain: throughout the range of the Molinia-Potentilla mire, this grass is a very common element in lowland Erico-Sphagnion blanket mires and Ericion tetralicis wet heaths and it shows a distressing tendency to increase its abundance in these vegetation types in certain circumstances, bring ing them very close in composition and structure to this community. Indeed, many references to a Molinietum or to ‘Molinia grassland’ in the British literature (e.g. Moss 1911, Rankin 1911a, b, Smith 1911a, Crampton 1911, Stapledon 1914, Jefferies 1915, Fraser 1933, Tansley 1939, McVean & Ratcliffe 1962, Meade 1981) and to other more precisely-defined units, like the Festuco-Molinietum of Evans et al. (1977) and the Molinia-Potentilla nodum of Bignal & Curtis (1981), include vegetation of this kind together with what is here termed Molinia-Potentilla mire, and bear ample testimony to the problems of separation of these different communities in the more oceanic parts of the country.

Synonymy

Rhacomitrio-Vaccinietum Smith 1905 p.p.; Rhacomitrium-Carex bigelowii nodum, Empetrum hermaphroditum faciès Poore & McVean 1957; Empetrum-hypnoid moss community Poore & McVean 1957, Rhacomitreto-Empetretum McVean & Ratcliffe 1962, Birks 1973; EmpeZrwm-hypnaceous moss heath McVean & Ratcliffe 1962; Alchemilla alpina-Vaccinium myrtillus nodum Birks 1973.

Constant species

Carex bigelowii, Deschampsia flexuosa, Empetrum nigrum ssp. hermaphroditum, Festuca ovina/vivipara, Galium saxatile, Vaccinium myrtilus, Hylocomium splendens, Pleurozium schreberi, Racomitrium lanuginosum, Rhytidiadelphus loreus, Cladonia uncialis.

Rare species

Anastrophyllum donianum, A. joergensenii, Bazzania pearsonii, Mastigophora woodsii, Plagiochila carringtonii, Scapania ornithopodioides.

Physiognomy

The Vaccinium myrtillus-Racomitritum lanuginosum heath brings together a variety of vegetation types in which Vaccinium myrtillus and/or Empetrum nigrum ssp. hermaphroditum, occasionally with other sub-shrubs, are co-dominant with Racomitrium lanuginosum or, in some stands, hypnaceous mosses. V. myrtillus is the commonest woody plant overall, although it is quite often subordinate in cover to E. nigrum ssp. hermaphroditum, the two forming a low mat, generally less than 1 dm thick, which has the appearance of a patchy mosaic of bushes growing among the moss carpet. V. vitis-idaea also occurs commonly in most types of Vaccinium-Racomitrium heath, though usually at low cover, and there is very occasionally some V. uliginosum. Calluna vulgaris is typically scarce throughout, though it becomes a little more common at lower altitudes, where the vegetation can approach the Calluna-Racomitrium heath (as on Skye: Birks 1973); Juniperus communis ssp. nana and Erica cinerea can also show local prominence in such stands. In other cases, Alchemilla alpina, which is quite a frequent plant through the Vaccinium-Racomitrium heath, attains co-dominance among the subshrubs. As well as these floristic differences, there is also considerable variation in the total cover of the woody mat, with vegetation at one extreme looking very obviously heathy, other stands resembling Carex-Racomitrium moss-heath with a local abundance of subshrubs (Poore & McVean 1957).

Floristic continuity in that particular direction is strengthened by the high frequency here of such vascular associates as Carex bigelowii, Festuca ovinalvivipara, Deschampsia flexuosa and Galium saxatile, although these plants are not generally as abundant as they can be in the Carex-Racomitrium heath: C. bigelowii sometimes occurs as scattered, quite large,

Synonymy

Carex hostiana-C. demissa nodum Poore 1955b; Carex demissa-C. panicea nodum Poore 19556 p.p.; Flush vegetation Holdgate 1955a p.p.; Turfy marshes Pigott 1956a; Gravel flushes Pigott 1956«; Calcareous marsh Sinker 1960; Carex panicea-Campylium stellatum nodum McVean & Ratcliffe 1962; Schoenus nigricans provisional nodum McVean & Ratcliffe 1962 p.p.; Kobresieto-Caricetum Ratcliffe 1965 p.p.; Gymnostometo-Caricetum Ratcliffe 1965; Caricetum lepidocarpae-hostianae Shimwell 1968a; Carex panicea-Campylium stellatum Association Birks 1973; Eriophorum latifolium-Carex hostiana Association Birks 1973; Schoenus nigricans Association Birks 1973 p.p.; Pinguiculo-Caricetum dioicae Jones 1973 p.p.; Carex fens Proctor 1974 p.p.; Pinguiculo-Caricetum dioicae Jones 1973 emend. Wheeler 1975; Schoenus nigricans Community Birse & Robertson 1976; Caricetum hostiano-pulicaris (Birse & Robertson 1976) Birse 1980; Carici dioicae-Eleocharitetum quinqueflorae (Birse & Robertson 1976) Birse 1980p.p.; Anagallis tenella-Equisetum variegatum Association Birse 1980; Campylio-Caricetum dioicae Dierssen 1982; Eleocharitetum quinqueflorae Dierssen 1982; Schoenus ferrugineus stands Wheeler et al. 1983 p.p.

Constant species

Carex dioica, C. hostiana, C. lepidocarpa, C. panicea, C. pulicaris, Eriophorum angustifolium, Juncus articulatus, Pinguicula vulgaris, Aneura pinguis, Bryum pseudotriquetrum, Campylium stellatum, Ctenidium molluscum, Drepanocladus revolvens.

Rare species

Bartsia alpina, Carex capillaris, Equisetum variegatum, Juncus alpinus, Kobresia simpliciuscula, Minuartia stricta, M. verna, Primula farinosa, Schoenus ferrugineus, Sesleria albicans.

Physiognomy

The Pinguiculo-Caricetum dioicae includes some of the most distinctive of our more calcicolous flush vegetation in which small sedges, dicotyledons and bryophytes predominate, usually forming the bulk of a short sward, often hummocky and open. Although there is a strong contingent of constant species, the community is very variable in its composition, showing some marked differences in the proportions of its more frequent species and in the representation of groups of plants preferential to particular habitats or regions. And, where certain of these species are abundant, they can have a striking effect on the physiognomy of the vegetation. The habitat conditions, too, can have a marked influence on the appearance of the community. Most stands are grazed and the herbage is accordingly often cropped very short; where herbivore pressure is not so high, the vegetation can have a more luxuriant look, hemicryptophyte dicotyledons especially making an obvious contribution.

Synonymy

Heather Moor Smith & Moss 1903, Smith & Rankin 1903 p.p.; Callunetum Lewis & Moss 1911, Elgee 1914, Tansley 1939, Fidler et al. 1970 p.p. Calluno-Ericetum einereae Bridgewater 1970 p.p.; Cladonio crispatae-Callunetum Coppins & Shimwell 1971 p.p.; Pohlio-Callunetum Shimwell 1975 p.p.

Constant species

Calluna vulgaris, Deschampsia flexuosa, Pohlia nutans.

Physiognomy

In the Calluna vulgaris-Deschampsia flexuosa heath, Calluna vulgaris is almost always the most abundant plant, though it often forms a fairly low, and sometimes quite open, canopy made up of immature individuals: burning is very common on the heathlands where this community occurs, many stands are of a more or less uniform age and relatively few are old enough to have mature or degenerate heather plants. Quite often, too, the cover shows signs of grazing with the heather nibbled close and both these factors have some influence on the contribution of other sub-shrubs. Typically, none of these associates is consistently frequent throughout, though certain species can become quite common and attain a measure of local abundance, if only exceptionally rivalling Calluna in their cover. Vaccinium myrtillus is the most important of these and, particularly where the community extends to higher altitudes, where the climate is cooler and more humid, its frequency and abundance presage a shift to the Vaccinium myrtillus-Deschampsia flexuosa heath. Much more locally, V. vitis-idaea and/or the hybrid V. x intermedium (Ritchie 1955Z?) can be found here, and Empetrum nigrum ssp. nigrum has sometimes spread in this kind of vegetation, as on Ilkley Moor in West Yorkshire (Fidler et al. 1970, Dalby et al. 1971). Erica cinerea and Ulex gallii, by contrast, are very scarce, although stands of the Calluna-Ulex gallii heath, of which both of these species are characteristic, do occur within the range of the Calluna-Deschampsia heath and can be difficult to separate from it. Erica tetralix is likewise rare, although it can figure locally in transitions to the Ericetum tetralicis, a fairly common feature in the mosaics of dry and wet heaths seen in the North York Moors (e.g. Elgee 1914).

Apart from Calluna, the only other vascular constant of the community is Deschampsia flexuosa but, even where the cover of the heather is fairly open, this is often represented by fairly sparse tufts and, under very dense canopies, it can be virtually extinguished.

Synonymy

Tufaceous mounds Holdgate 1955a p.p.; Cratoneuron commutatum-Saxifraga aizoides nodum McVean & Ratcliffe 1962, Birks 1973; Cratoneuron springs Ferreira 1978; Cratoneuron drip-zones Ferreira 1978; Cratoneuron commutatum Community Birse 1980; Cratoneuron filicinum Community Birse 1980.

Constant species

Festuca rubra, Bryum pseudotriquetrum, Cratoneuron commutatum.

Physiognomy

Cratoneuron commutatum occurs frequently and with a measure of local abundance in a variety of calcareous mires, but in the Cratoneuron commutatum-Festuca rubra spring it is consistently dominant in large swelling masses, often forming prominent mounds or banks, of a golden-green colour grading to orange-brown. In some stands, which seem to preserve the same general floristic composition, C. filicinum accompanies or totally replaces it: the two species can show intergradations, and indeed both exhibit wide intraspecific variation (Bell & Lodge 1963, Smith 1978) but, by and large, C. filicinum is a smaller and somewhat stiffer plant and its stem leaves are plicate.

Other bryophytes can make a contribution to the mat, though typically it is a minor one. However, Bryum pseudo triquetrum is very common and occasional include Philonotis fontana and the distinctly calcicolous P. calcarea, Aneura pinguis, Pellia endiviifolia, Drepanocladus revolvens, Gymnostomum recurvirostrum, G. aeruginosum, Brachythecium rivulare and Dicranella palustris. Very typically, there is some tufa deposition among the bryophyte shoots, which lends the mat a distinctive crunchy texture and allows it to build up into mounds.

The vascular element of the vegetation is typically species-poor and of low total cover with, in many stands, just a few scattered herbs. But there is consider able variation in this associated flora from place to place and, particularly where stands are developed over gently-sloping ground, a richer and more extensive herb layer can be found, such that the vegetation comes close to the Cratoneuron-Carex spring or to a Caricion davallianae flush. Often, however, the only species present are Festuca rubra, Cardamine pratensis and Saxifraga aizoides. The last can be quite conspicuous here, particularly when it has its yellow summer flowers, but it is generally present only in small amounts and is totally absent from springs of this kind throughout southern Scotland (e.g. Meek 1976, Ferreira 1978) and in Wales.

Occasional herbs include Agrostis stolonifera, Deschampsia cespitosa, Equisetum palustre, Chrysosplenium oppositifolium, Poa trivialis, Carex panicea, C. nigra, C. dioica and the rare Epilobium alsinifolium and Equisetum variegatum.

Synonymy

Koenigia islandica-Carex demissa nodum Birks 1973.

Constant species

Carex demissa, Deschampsia cespitosa, Juncus triglumis, Koenigia islandica, Saxifraga stellaris, Blindia acuta, Scapania undulata.

Rare species

Juncus biglumis, Koenigia islandica, Sedum villosum.

Physiognomy

Since it was first found in Britain in 1934 and finally accurately determined in 1950 (Burtt 1950, Raven & Walters 1956), Koenigia islandica has been observed on and around The Storr in Skye, where it was first collected, on other parts of the Trotternish ridge there (Birks 1973) and on Mull (Birse 1984), in a variety of vegetation types. In certain cases it is best seen as an occasional, sometimes of quite high local cover, in communities which occur widely elsewhere: some stands, for example, can be placed in the Philonoto-Saxifragetum, while others are very similar to the Festuca-Agrostis-Alchemilla or Carex-Poly trichum grassheaths. Others, however, are more peculiar and it is these which are gathered into this Carex demissa-Koenigia islandica community.

It is an open vegetation type, with a bryophytedominated carpet broken by areas of wet, silty and stony ground. Scapania undulata, Calliergon sarmentosum and Blindia acuta are all common and each can be abundant, with occasional patches of Dicranella palustris, Philonotis fontana, Drepanocladus revolvens, Marsupella aquatica and Sphagnum auriculatum. Scattered through this mat and over the rills themselves are plants of Carex demissa, Koenigia, Deschampsia cespitosa, Saxifraga stellaris, Juncus triglumis, J. bulbosus and the rare J. biglumis and Sagina saginoides. All of these are generally of low cover, though many can show a measure of abundance and Koenigia itself, though its individual plants are little more than a few centimetres across, can cover quite an area of ground.

Habitat

In common with many of the other situations in which Koenigia is found, both in this country and elsewhere, the Carex-Koenigia community occurs on ground which is kept periodically moist by circumneutral and oligotrophic waters. Typically, it is found in open silty or stony flushes fed by vigorous seepage from spings issuing at moderately high altitudes, over 500 m, from the basalt of the Trotternish ridge.

Other vegetation of the same general type as the Hyperico-Potametum and characteristic of similar, seasonallyinundated habitats with rather base-poor and only moderately enriched waters, undoubtedly occurs in Britain, but it has been very poorly sampled. Some, lacking Hypericum elodes but otherwise essentially the same as the Hyperico-Potametum, could perhaps be regarded as impoverished stands of that community, though it must be noted that species such as Potamogeton polygonifolius, Eriophorum angustifolium, Juncus bulbosusfkochii and Sphagnum auriculatum also occur with some frequency in bog-pool and poor-fen vegetation.

Then, there are stands in which Eleocharis multicaulis is strongly dominant with little or no H. elodes or P. polygonifolius, and some at least of these look very similar to the Eleocharitetum multicaulis Tüxen 1937 which has been recorded from Eire (Braun-Blanquet & Tüxen 1952, Brock et al. 1978, van Groenendael et al. 1979; see also Ivimey-Cook & Proctor 19666) and from other parts of western Europe (Schoof van Pelt 1973,

Dierssen 1975, 1982). White & Doyle (1982) list Deschampsia setacea as a characteristic species of such vegetation and this national rarity is certainly typical, in Britain, of this general kind of habitat. Scirpus fluitans can also be found dominating in swards which lack some of the most typical Hyperico-Potametum plants and, in the New Forest and Cornwall, Baldellia ranunculoides is a frequent and conspicuous component of low-growing vegetation in seasonally-wet pools. In the Burren, the latter kind of assemblage was designated the Baldellio-Littorelletum by Ivimey-Cook & Proctor 19666, although there the habitat was characterised by baserich and calcareous waters.

In the latest revision of the Littorelletalia by Dierssen (1975), all these vegetation types are grouped together with the Hyperico-Potametum in the Hydrocotylo-Baldellion alliance, a group comprising assemblages of mesotrophic to oligotrophic, and periodically-fluctuating waters. Other Littorelletalia communities, mostly falling in the Isoetion lacustris and Lobelion dortmannae, are dealt with in the chapter on aquatic vegetation.

Synonymy

Callunetum arenosum Tansley 1911 p.p:, Callunetum Farrow 1915, Watt 1936; Callunetum arenicolum Tansley 1939 p.p.

Constant species

Calluna vulgaris, Festuca ovina, Dicranum scoparium, Hypnum cupressiforme s.l.

Physiognomy

The Calluna vulgaris-Festuca ovina heath is a heatherdominated community, very poor in vascular associates, though sometimes showing a modest diversity among the bryophytes and, more especially, the lichens. Calluna vulgaris is usually the only woody species present and invariably the most abundant. More particularly, Erica cinerea, Ulex minor and U. gallii, which become important constituents of the sub-shrub component of dry heaths further to the south and west, are largely excluded here. They sometimes figure in stands on or near the East Anglian coast, and the first two can occasionally be found in the few stations for the community south of the Thames, but the general scarcity of these species furnishes a good diagnostic criterion, provided that it is remembered that they can be locally eliminated from richer heath types to produce the kind of virtually pure Calluna that is usual here. Another general absentee is Erica tetralix'. this becomes increasingly prominent through the whole range of wet and humid heaths towards south-west Britain but is very scarce here and strictly limited to those rather unusual situations where there is a transition to soils with impeded drainage. Ulex europaeus is likewise uncommon, though it can become locally abundant where there has been some disturbance, not necessarily recent, as along trackways or around the margins of plantations.

However, although it is Calluna which gives this community its distinctive stamp, the cover and height of the canopy are very variable. This affects not only the gross appearance of the vegetation, which can have a canopy of living heather anything between 10 and 100 cm tall, covering 50-100% of the ground, but it also has a controlling influence on the variety, abundance and distribution of the associated flora, which is for the most part confined to areas between the Calluna clumps and to the centre of those bushes which are collapsing with age or showing early regeneration from the stools or seed.

Synonymy

Pohlia ‘glacialis’ spring Ratcliffe 1964; Pohlia albicans vax. glacialis spring Ratcliffe 1977.

Constant species

Deschampsia cespitosa, Saxifraga stellaris, Pohlia ludwigii, P. wahlenbergii var. glacialis.

Rare species

Alopecurus alpinus, Cerastium cerastoides, Epilobium alsinifolium, Phleum alpinum, Pohlia ludwigii, P. wahlenbergii var. glacialis.

Physiognomy

Pohlia wahlenbergii var. glacialis can be found as an infrequent and low-cover associate in a variety of vegetation types of wet ground through the uplands of north-western Britain but, in the Pohlietum glacialis, it dominates in spongy carpets, often of quite small extent, but exceptionally covering up to 200 m2, of a bright apple-green colour that makes the stands readily recognisable from a distance. Few other bryophytes occur with any frequency and none is consistently abundant. There is commonly a little P. ludwigii and Philonotis fontana sometimes attains a measure of prominence, though typically it is of nothing like such high cover as in the Philonoto-Saxifragetum. Other bryophytes recorded occasionally are Hygrohypnum luridum, Bryum weigelii, Calliergon stramineum, Scapania undulata, S. uliginosa, Dicranella palustris and Marchanda alpestris.

In this carpet, vascular plants are few in number and typically of low cover. Only Deschampsia cespitosa (presumably ssp. alpina at the high altitudes characterised by this community) and Saxifraga stellaris are constant, but the rare Arctic-Alpine Cerastium cerastoides is quite often found and there can also be some Stellaria alsine, Chrysosplenium oppositifolium, Epilobium anagallidifolium, Veronica serpyllifolia var. humifusa and Rumex acetosa. Other rare plants which find an occasional locus here are Epilobium alsinifolium, Alopecurus alpinus and Phleum alpinum.

Habitat

The Pohlietum is strictly confined to spring-heads associated with the late snow-beds of the higher reaches of the Scottish Highlands, where there is vigorous irrigation by cold, oligotrophic waters.

Although P. wahlenbergii var. glacialis occurs in small amounts over quite a wide range of altitudes through the uplands of north Wales, Cumbria and Scotland, it is found with the kind of dominance characteristic here only within the high-montane zone, at altitudes generally above 850 m, where mean annual maximum temperatures do not exceed 21 °C (Conolly & Dahl 1970).