Constant speces

Bidens tripartita, Filaginella uliginosa, Phalaris arundinacea, Polygonum amphibium, Polygonum hydropiper.

Physiognomy

The Polygono-Bidentetum comprises stands of open or closed vegetation variously dominated by Bidens tripartita, Polygonum amphibium or P. hydropiper. Other knotweeds are typically scarce but P. persicaria sometimes occurs. Filaginella uliginosa is constant but generally at low cover and there are very often some sparse shoots of Phalaris arundinacea. Alopecurus geniculatus and Agrostis stolonifera are quite common, occasionally forming dense mats of shoots and Callitriche hamulata occurs frequently. Other occasionals include Alisma plantagoaquatica, Myosotis laxa ssp. cespitosa, Juncus bufonius, Plantago major, Potentilia anserina and Stellaria alsine.

Habitat

The Polygono-Bidentetum is characteristic of periodically-flooded, eutrophic silts and clays towards the limit of inundation around fluctuating ponds, lakes and reservoirs.

It is the combination of periodic inundation and high levels of nitrogen in waters and/or substrates favoured by the ephemeral species of this assemblage that invade as flooding subsides. Typically, inundation occurs in winter or at least more extensively then, so that exposure of a damp, fertile substrate coincides with the warmer temperatures of spring for germination of the annual plants. In fact, some frequent species in this community are perennials, like Polygonum amphibium and Phalaris arundinacea, occurring at generally low covers but maintaining themselves towards the upper limits of flooding.

Small stands of ephemeral vegetation with an often open cover of annuals and short-lived perennials occur patchily on British salt-marshes. Recurrent assemblages are rare and there seems to be a large element of chance in the floristic composition, early arrivals frequently preempting the niche. Such vegetation may include Sagina maritima, S. nodosa and Plantago coronopus, more rarely Bupleurum tenuissimum (to the south-east) and Centaurium littorale (to the north) and provide a salt-marsh context for ephemerals such as Cochlearia danica and Desmazeria marina which also occur in other maritime habitats.

Breaks in the turf of mid-and upper-marsh communities provide the most usual habitat for such species and they are especially characteristic of old turf-cuttings where they form part of the sequence of recolonising vegetation giving way to mixtures of Festuca rubra, Agrostis stolonifera, Puccinellia maritima and Potentilla anserina, which come to approximate to the Puccinellietum maritimae, the Juncetum gerardi or the Festuca-Agrostis-Potentilla mesotrophic grassland. Such ephemerals also occur in disturbed situations around reclamation banks (e.g. Gray 1977, 1979, Adam & Akeroyd 1978).

This kind of vegetation is the nearest equivalent in Britain to similarly diverse assemblages on Continental salt-marshes which have been assigned to the Saginion alliance in the Saginetea maritimae Westhoff, van Leeuwen & Adriani 1962 (e.g. Beeftink 1962, 1965, 1975, 1977a; Tüxen & Westhoff 1963; Westhodd & den Held 1969).

Constant species

Alopecurus geniculatus, Rorippa palustris.

Physiognomy

A mat of Alopecurus geniculatus, often extensive and lush, is the most distinctive characteristic of the Ranunculo-Alopecuretum, with sometimes a small contribution to the carpet from Potentilla anserina, Poa trivialis and Ranunculus repens. There are frequent scattered plants of Rorippa palustris and various annual knotweeds, among which Polygonum lapathifolium, P. aviculare and P. hydropiper are the most common. Rumex crispus also occurs often and there can be some Elymus repens and Phalaris arundinacea, though these are generally not very abundant. A wide range of plants of damp, weedy places occur at low frequency.

Habitat

The Ranunculo-Alopecuretum is typical of periodically-flooded sills and sands on terraces, bars and islands in mature river valleys, on the edges of seasonal pools and small gentle streams in the lowlands and around fluctuating ponds and lakes with more nutrient-rich waters. Modest trampling by people, stock or wildfowl can be important in maintaining open ground for this vegetation and for dispersal of propagules.

Flooding by river or lake waters or the seasonal accumulation of rainwater in shallow depressions can handicap the growth of pasture vegetation or leave deposits of silt and sand around shores and on the terraces of river valleys. Then the species of this community are often able to take rapid advantage of the areas of bare ground thus created, by germination of seed and spread of vegetative propagules.

Synonymy

Festucetum (rubrae) auct. angl.

Constant species

Festuca rubra, Plantago maritima, Glaux maritima.

Physiognomy

The closed grasslands of the Juncetum gerardi are normally dominated by mixtures of Festuca rubra and Agrostis stolonifera with a variety of herbaceous associates among which Plantago maritima, Glaux maritima, Armeria maritima and Triglochin maritima are generally the most frequent and abundant. Juncus gerardii itself is present in varying amounts: it is usually constant through all but the most anomalous of the Juncetum swards and in some cases is dominant or co-dominant. In certain subcommunities, there are frequent records for low-marsh species and an algal mat is often conspicuous over the substrate surface. In other sub-communities, a group of mesotrophic grassland and flush species are well-represented. The Juncetum gerardi is the community within which bryophytes reach their lowest limit on salt-marshes.

Sub-communities

As in the other major British salt-marsh association, the Puccinellietum maritimae, variation is virtually continuous, largely based on quantitative differences among relatively few species and frequently including a site-specific element reflecting local histories of marsh use. The following sub-communities should therefore be seen as foci of national variation with somewhat hazy boundaries.

Puccinellia maritima sub-community: Juncus gerardii-Puccinellia maritima nodum Adam 1976; Puccinellietum maritimae agrostidetosum Beeftink 1962. This sub-community comprises generally short swards which are floristically transitional between the Juncetum gerardi and the Puccinellietum maritimae. J. gerardi, Puccinellia maritima, Festuca rubra, Plantago maritima, Glaux maritima and Triglochin maritima are constant and varying proportions of these species co-dominate.

The sampling and analysis of salt-marsh vegetation

The herbaceous vascular vegetation on the intertidal silts and sands of salt-marshes is one of the most frequently used illustrations of ecological pattern but there are considerable difficulties in producing an adequate national classification of the plant communities of this distinctive habitat.

First, much salt-marsh vegetation is species-poor. There is little problem in sampling and sorting monospecific stands but, in many cases, a small number of species occur with varying abundance in a wide variety of combinations on salt-marshes. Early accounts of this vegetation (e.g. Tansley 1911, 1939) relied heavily on dominance in an attempt to make sense of such variation, but, as Dalby (1970) noted, this may obscure patterning among less conspicuous species that it is sensible to try and interpret. Furthermore, there has been a tendency in Britain to lump more complex vegetation, less susceptible to analysis, into a ‘general salt-marsh’ community. This term has sometimes been applied in its original, broad sense (Tansley 1911) to vegetation ‘not dominated by any single species, except locally’ and varying ‘from place to place according to local conditions and to the accidents of colonisation by different species’; on other occasions (e.g. Chapman 1934), it has been used to denote a more clearly-defined community.

Second, on many salt-marshes there is a site-related element in the floristic variation among the communities which reflects particular local histories of marsh use or unique combinations of environmental conditions.

Constant species

Poa annua, Senecio vulgaris.

Physiognomy

The Poa annua-Senecio vulgaris community brings together a variety of weed assemblages which are distinctive in their combinations of common species rather than by the presence of striking differentials. Poa annua and Senecio vulgaris are the only constants throughout but Lolium perenne is very frequent and Capsella bursa pastoris and Cerastium fontanum occur commonly in various sub-communities. Occasionals include Cirsium arvense, Plantago major, Poa trivialis, Veronica persica and Urtica dioica. The assemblages vary in their total cover and, though most of the more frequent species here are emphemeral, a perennial grassy element can be seen establishing in some sub-communities.

Sub-communities

Polygonum persicaria-Ranunculus repens sub-community. The abundance of knotweeds and spurges is often the most striking feature here, with Polygonum aviculare and, more strongly preferential, P. persicaria both constant, Euphorbia helioscopa and E. exigua frequent. Stellaria media is also more common in this sub-community than elsewhere with Ranunculus repens, Anagallis arvensis, Viola arvensis, Bilderdykia convolvulus, Anthemis cotula, Trifolium repens and Lapsana communis. Preferential occasionals include Sinapis arvensis, Raphanus raphanistrum, Spergularia arvensis and Fumaria officinalis.

Polygonum aviculare-Matricaria perforata sub-community. P. aviculare remains constant here with P. persicaria and P. arenastrum occasional, but more striking is the high frequency and often abundance of mayweeds: Chamomilla suaveolens, C. recutita and M. perforata are all common in this sub-community. Chenopodium album and Coronopus squarratus are also weakly preferential.

Synonymy

Tripleurospermum inodorum stands Kay 1994 p.p.

Constant species

Matricaria perforata, Polygonum aviculare, Stellaria media.

Physiognomy

The Matricaria perforata-Stellaria media community comprises annual vegetation dominated by mixtures of Stellaria media, Polygonum aviculare and Matricaria perforata. Also quite frequent overall but variously represented in the different sub-communities are Poa annua, Elymus repens, Bilderdykia convolvulus and Sonchus asper. Occasionals of the community include Cirsium arvense, Atriplex patula, Raphanus raphanistrum and Urtica dioica. Acrocapous mosses are sometimes conspicuous on bare ground, Bryum rubens, Barbula unguiculata and Dicranella staphylina being recorded most commonly.

Sub-communities

Anagallis arvensis-Viola arvensis sub-community. The vegetation here tends to be quite species-poor but enlivened by the pretty flowers of Viola arvensis and Anagallis arvensis.

Poa annua-Galeopsis tetrahit sub-community. P. annua shows its peak of frequency here with Galeopsis tetrahit, Cerastium fontanum and Elymus repens also frequent, Aphanes arvensis and Juncus bufonius occasional.

Elymus repens-Potentilla anserina sub-community. E. repens and Poa annua both remain frequent in this subcommunity but Agrostis stolonifera also becomes common, along with Potentilla anserina and Equisetum arvense. Also more frequent, though showing their peak of occurrence in the next sub-community, are Bilderdykia convolvolus, Chenopodium album, Capsella bursapastoris, Chamomilla suaveolens, Trifolium repens and Veronica persica. Lamium purpureum, Bromus sterilis, Tussilago farfara and Ranunculus arvensis are more distinctive occasionals.

Bilderdykia convolvulus-Veronica persica sub-community: Lycopsietum arvensis (Raabe 1944) Passarge 1964 sensu Silverside 1977; Alchemillo-Matricarietum chamomillae R.Tx. 1937 emend. Passarge 1957 sensu Silverside 1977.

Spartina alterniflora is a naturalised alien in Europe first recorded in Britain in 1829 from the river Itchen, Hampshire (Marchant & Goodman 1969b). By the turn of the century, it had spread to occupy extensive areas of Southampton Water and occurred as far east as Chichester Harbour in Sussex (Rankin in Tansley 1911, Marchant & Goodman 1969b). Since then it has declined, at least partly in response to land reclamation (Marchant 1967) though perhaps also as a result of invasion by Spartina anglica, the fertile amphidiploid which arose from hybridisation between S. alterniflora and S. maritima.

S. alterniflora now survives only at Marchwood, Hampshire, and as transplanted clumps in the Spartina Garden in Poole Harbour, Dorset (Marchant & Goodman 1969b). The natural stand comprises a dense cover of S. alterniflora shoots with some Spartina anglica, Puccinellia maritima and Aster tripolium (Beeftink & Géhu 1973, Géhu & Delzenne 1975). The association occurs in scattered localities down the Atlantic coast of western Europe and is characteristic of situations with a lower and more variable salinity than other Spartina-dominated communities (Beeftink & Géhu 1973). The Marchwood stand has been placed in the sub-association asteretosum tripolii which has also been recorded from Brittany and Spain (Beeftink & Géhu 1973, Géhu & Delzenne 1975, Kortekaas et al. 1976).

The sampling and analysis of the vegetation

Sand dunes occur widely around the British coast and, from the beginnings of plant ecology in this country, attracted sufficient attention for Tansley (1939) to be able to outline some of the major vegetation types encountered there and to sketch out a successional line that remains a commonly invoked example of serai development.

Necessarily, perhaps, the understanding of pattern and process in this distinctive landscape was dominated in these early years by studies of a few particular sites like Braunton Burrows on the Somerset coast, the Southport dunes and north Norfolk (e.g. Oliver 1913; Watson 1918; Salisbury 1922, 1925; Pearsall 1934). With the vegetation of coastal shingle which figured from the start in these enquiries, it was again striking sites like Blakeney and Chesil Beach which received attention (Oliver 1911, 1913; Watson 1922; Richards 1929). Further painstaking investigation of some of these and a very few other sites, like Newborough Warren on Anglesey, has yielded an informative understanding of the ecology of important aspects of the dune habitat (e.g. Ranwell 1959, 1960a, b; Willis et al. 1959a, b; Willis & Yemm 1961) but without any wider descriptive framework of dunes throughout Britain in which to contextualise the picture of vegetation types emerging. More broadly, Scottish sand dunes figured little in our view of these communities until Gimingham's (1964a) overview.

With something as complex and variable as vegetation, no key can pretend to offer an infallible short cut to diagnosis. The following should thus be seen as simply as a crude guide to identifying the types of vegetation found on salt-marshes and must always be used in conjunction with the data tables and community descriptions. It relies on floristic (and, to a lesser extent, physiognomic) features of the vegetation and demands a knowledge of the British vascular flora. It does not make primary use of any habitat features, though these may provide a valuable confirmation of a diagnosis.

Because the major distinctions between the vegetation types in the classification are based on inter-stand frequency, the key works best when sufficient samples of similar composition are available to construct a constancy table. It is the frequency values in this (and, in some cases, the ranges of abundance) which are then subject to interrogation with the key.

Samples should always be taken from homogeneous stands and be 2 × 2 m or 4 × 4 m according to the scale of the vegetation or, where stands are irregular, of identical size but different shape.

Synonymy

Juncetum maritimi auct. angl. p.p., includes Juncus maritimus-Oenanthe lachenalii ass. R.Tx. 1937

Constant species

Agrostis stolonifera, Festuca rubra, Glaux maritima, Juncus gerardii, J. maritimus.

Physiognomy

The association is dominated by tall dense clumps of Juncus maritimus with an understorey of Agrostis stolonifera, Festuca rubra, Glaux maritima and Juncus gerardii. There is a rich subsidiary flora in which mesotrophic grassland species (notably Leontodon autumnalis and Trifolium repens) and weed species (for example, Atriplex hastata, Elymus repens and Rumex crispus) are conspicuous. Bryophytes may be locally abundant with patches of Calliergon cuspidatum, Amblystegium riparium, A. serpens and Eurhynchium praelongum. Stands of the association may be based on individual clones of J. maritimus, in some cases up to 15 m in diameter, or occur as an extensive zone.

Sub-communities

Plantago maritima sub-community: Juncetum maritimi Yapp & Johns 1917; Festuca rubra-Juncus maritimus nodum Adam 1976. Plantago maritima and Triglochin maritima attain constancy in the often luxuriant vegetation of this sub-community and there are frequent records for Leontodon autumnalis, rayed Aster tripolium and Armeria maritima. It sometimes occupies extensive areas, notably at Ynys Hir in the Dovey estuary, Dyfed.

Oenanthe lachenalii sub-community: Juncus maritimus-Oenanthe lachenalii ass. R.Tx. 1937; Oenanthe lachenalii-Juncus maritimus nodum Adam 1976. Triglochin maritima, Leontodon autumnalis and Oenanthe lachenalii are constant here, the last giving a particularly distinctive appearance to the vegetation in the flowering season, though it is rarely present in abundance.

Synonymy

Dune grassland Tansley 1911, 1939, Gimingham 1964a; Dune pasture Gimingham 1964a p.p.; Machair Gimingham 1964a, 1974, Ran well 1974; Euphrasio-Festucetum arenariae Birse 1980; Astragalo-Festucetum arenariae Birse 1980 p.p.

Constant species

Festuca rubra, Galium verum, Lotus corniculatus, Plantago lanceolata, Poa pratensis, Trifolium repens.

Rare species

Acaena novae-zelandiae, Astragalus danicus, Dianthus deltoides, Epipactis atrorubens, Mibora minima, Oxytropis halleri, Primula scotica.

Physiognomy

The Festuca rubra-Galium verum community consists of dune vegetation in which Festuca rubra and a variety of other grasses, dicotyledons and mosses make up a generally closed sward, occasionally rank, but usually just a decimetre or two tall, and sometimes closely cropped to a short, tussocky turf. Ammophila arenaria, the usual dominant with us on more mobile sand, remains common overall, but it is no longer a constant feature of the vegetation: indeed, in some sub-communities here, it is only occasional. Moreover, even where it is still frequent, the cover is rarely extensive and often reduced to small tufts of shoots noticeably lacking in vigour. F. rubra, by contrast, is usually abundant, the typical dominant in the sward, and commonly recorded as var. or ssp. arenaria with its far-creeping rhizome systems and rather lax tussocks of stiff leaves (Hubbard 1968, Tutin et al. 1980). Other grasses are generally subordinate but some can be quite common. Poa pratensis agg., for example, often obviously P. subcaerulea, is a constant of the community, though only exceptionally of more than moderate cover, and in regions of moister climate Holcus lanatus becomes very frequent.

Synonymy

Calliergon cuspidatum-Salix repens nodum Jones 1992 p.p.; Young dry slack nodum Jones 1992

Constant species

Carex arenaria, Juncus articulatus, Leontodon hispidus, Sagina nodosa, Salix repens, Aneura pinguis, Bryum pseudotriquetrum.

Rare species

Equisetum variegatum, Pyrola rotundifolia, Moerckia hibernica, Petalophyllum ralfsii.

Physiognomy

The Sagina nodosa-Bryum pseudotriquetrum dune-slack community comprises short and often rather open swards dominated by a low and patchy cover of Salix repens, a patchy turf of grasses and diminutive herbs and a sometimes extensive contingent of mosses and thalloid liverworts. The vegetation is typically submerged briefly and to shallow depths in the winter and it is on the bare damp patches of sand and shell debris exposed as the water level falls that the various ephemerals and less competitive bryophytes of the community can gain a hold.

Apart from S. repens, the commonest vascular perennials are Carex arenaria, Juncus articulatus and Agrostis stolonifera, all typically represented by sparse shoots, with small scattered rosettes of Leontodon hispidus. Among these, by late spring, there are often numerous tiny plants of Sagina nodosa with the more prominent Centaurium eythraea. Seedlings of Rubus caesius occasionally figure and there are sparse plants of Samolus valerandi, Mentha aquatica, Carex serotina, Equisetum palustre and Taraxacum officinale agg. Ammophila arenaria is typically very scarce in this vegetation and of insignificant cover.

Synonymy

Ammophiletum arenariae Tansley 1911, 1939 p.p.; Elymo-Ammophiletum arenariae Br.-Bl. & De Leeuw 1936 p.p.; Leymus arenarius consocies Bond 1952; Ammophila arenaria stands Gimingham 1964a p.p.; Potentillo-Elymetum arenariae (Raunkiaer 1965) Tx. 1966 sensu Birse 1980.

Constant species

Leymus arenarius.

Physiognomy

The Leymus arenarius community consists of open to locally dense stands of dune vegetation dominated by the tall and tussocky perennial grass Leymus arenarius. It is a rhizomatous plant, able to colonise and fix mobile sand and keep pace with substantial accumulation by upward and outward extension of its stout buried stems, such that the robust glaucous shoots, often well over 1 m high, can be found emerging from dunes that have grown to several metres tall (Trail 1904, Bond 1952).

No other species is constant throughout, but Elymus farctus is locally common, invading foreshore sand ahead of or together with the Leymus and sometimes remaining as a subsidiary and shorter element to the cover here, though only thickening up in vegetation which is best regarded as transitional to Elymus farctus foredunes. Ammophila arenaria is likewise never a prominent feature here, but it is a characteristic colonist of wind-blown sand along with or subsequent to Leymus and can be found as an occasional in the community, going on to exceed the lyme grass in frequency and abundance among the various kinds of Ammophila dunes. Then, in some stands, Festuca rubra is quite common with Elymus repens sometimes marking out places where there has been incorporation of organic detritus.

Synonymy

Spergula arvensis-Lamium amplexicaule community Sissingh 1950

Constant species

Capsella bursa-pastoris, Chenopodium album, Poa annua, Senecio vulgaris, Stellaria media, Urtica urens.

Rare species

Erodium moschatum, Medicago polymorpha, Sisymbrium irio.

Physiognomy

In the annual vegetation of the Urtica urens-Lamium amplexicaule community, the usual dominants are Stellaria media, Poa annua or Capsella bursa-pastoris, with Chenopodium album making a very frequent but somewhat more variable contribution to the cover, Senecio vulgaris and Urtica urens constant but generally of less abundance.

Also frequent, sometimes with locally high cover, are Lamium amplexicaule, Solanum nigrum and the now widely naturalised Galinsoga parviflora, a South American plant which escaped from Kew around 1860 (Salisbury 1964). Spergula arvensis, Veronica persica, Matricaria perforata, Chamomilla suaveolens, Polygonum aviculare and Elymus repens are common, too, though usually at low cover and another South American introduction, Solanum sarrachoides, is occasional. Polygonum persicaria, Sonchus oleraceus, S. asper and Bilderdykia convolvulus are scarce companions.

More locally, this vegetation can show a very distinctive enrichment from a variety of ‘shoddy aliens’. These are plants whose seed was brought in with rags from different parts of Europe, the waste from which, after recovery of wool fibre, was dumped or spread on fields as a fertiliser.

Synonymy

Caricetum arenariae Tansley 1939 p.p.

Constant species

Carex arenaria, Cornicularia aculeata.

Rare species

Astragalus danicus, Corynephorus canescens.

Physiognomy

The Carex arenaria-Cornicularia aculeata community includes lichen-rich swards in which sand-sedge is the only constant vascular plant. It is, though, never a vigorous dominant here, only occasionally having high cover and more usually occurring as scattered tufts of shoots, sometimes distinctly moribund. Neither are any other herbs consistently abundant. Festuca ovina and F. rubra are quite commonly found, for example, but usually as small scattered tussocks and, though Agrostis capillaris occasionally forms patches in the turf, these are rarely dense. Then, although Luzula campestris is fairly frequent, it generally occurs as rather sparse individuals. Sometimes more abundant, though only very locally around the East Anglian coast, is the rare grass Corynephorus canescens which, while being essentially a pioneer plant of more open sands, can continue to seed into these swards for several years (Marshall 1967). Certain annual grasses like Aira praecox, A. caryophyllea and Phleum arenarium may also occur with considerable local abundance where bare patches develop. Finally, among the monocotyledons, Ammophila arenaria is a frequent feature of coastal stands of the community though, even more than Carex arenaria, it is characteristically of very debilitated growth, persisting as sparse, scattered tussocks.