Maritime grassland/heath

Maritime vegetation

The vegetation on cliff-tops is probably the closest to “natural” that is present in the UK (and indeed the whole of Western Europe). Most perennial, slow growing maritime species occur on sea cliffs not because they have a requirement for salt or any other physical or chemical characteristic of this habitat but because they are competitively inferior to faster growing inland species. High salinity reduces the vigour or kills terrestrial species and creates an extreme environment, with a low intensity of competition, in which this suite of competitively inferior “maritime” species can survive.

The maritime cliff communities of the NVC were described in Volume 5 of British Plant Communities, first published in 2000, along with the other maritime communities (those of shingle strand-line and sand-dunes and saltmarshes) and vegetation of open habitats.

In total, 12 maritime cliff communities have been identified.

The maritime cliff communities consist of three subgroups:

five maritime cliff crevice and ledge communities (MC1, MC2, MC3, MC4 and MC5)
five maritime grassland communities of sea-cliffs (MC8, MC9, MC10, MC11 and MC12)
two communities associated with sea-bird cliffs (MC6 and MC7)

The heath communities of the NVC were described, along with the mire communities, in Volume 2 of British Plant Communities, first published in 1991.

In total, 22 heath communities have been identified.

The heath communities consist of six separate subgroups:

five lowland dry heath communities, all with distinct, largely non-overlapping distributions in England and Wales (H1, H2, H6, H8 and H9)
three localised communities, with non-overlapping ranges in southern England, which are considered transitional between the above and the wetter communities classified in the NVC as mires (H3, H4 and H5)
two maritime heath communities, found exclusively on the coasts of northern and western Britain; one (H7) is more widespread than the other (H11)
four submontane heaths from upland areas in northern and western Britain; two of these (H10 and H12) are widespread, whereas the other two (H16 and H21) are more localised (confined to Scotland, and Scotland and the Lake District, respectively)
two sub-alpine communities, considered transitional between the previous and next groupings - H18, which is widespread in northern and western Britain), and H22, which is confined to Scotland
six montane heath communities with lichens and mosses, all of which are confined either to Scotland (H13, H14, H15, H17 and H20) or to Scotland and the Lake District (H19)

The woodland and scrub communities of the NVC were described in Volume 1 of British Plant Communities, first published in 1991.

In total, 25 woodland/scrub communities have been identified, consisting of 19 woodland communities, four communities classed as scrub and 2 as underscrub.

The woodland communities consist of:

Six mixed deciduous or oak/birch woodland communities, which between them are found throughout Britain
Three Beech woodland communities, found mainly in southern England
A Yew woodland community, almost completely restricted to southeast England (community W13)
A Scots Pine woodland community, restricted to Scotland
A Juniper woodland community (community W19)
Seven wet woodland communities, characterised by the presence of alder, birch and willows (communities W1, W2, W3, W4, W5, W6 and W7).
Communities of arctic-alpine willows

The scrub communities consist of:

Communities consisting of shrubs such as hawthorn, blackthorn and elder
Gorse and broom scrub

The underscrub communities consist of bramble and bracken underscrub.

A further scrub community, SD18, dominated by Sea Buckthorn, is classified among the sand-dune communities.

Maritime grasslands

In the most exposed locations, typical of the UK’s Atlantic facing sea cliffs, the effects of salt spray often override those of geology and soil type but the latter still have a significant impact on the habitat and hence the vegetation. Some cliffs only have a thin layer of soil and so conditions for flowering plants are extremely difficult. As soil thickness increases and the extreme influences of the maritime environment ameliorate this allows the development of true maritime grasslands (MC8 and onwards in the NVC system).

The MC8 Festuca rubra-Armeria maritima maritime grassland

The MC8 Festuca rubra-Armeria maritima maritime grassland is the most salt tolerant of the true grassland communities. This community is typical of steep to moderate slopes, up to 50m above sea level and still receives large amounts of sea spray. MC8 grasslands are UK-wide in their occurrence as they are found on a wide range of rock types. Soils are generally brown rankers, moderately deep and rich in rock fragments and organic matter (derived from the bulky grass mattress) and of neutral pH. MC8s may extend down to spray-splashed cliffs where there may be a transition to crevice communities as the soil thins. Where red fescue dominates the sward it is like a bouncy mattress and is a delight to walk or sit on, botanically it is not so interesting as it is usually extremely species poor. On shallower soils with a sunnier aspect richer assemblages of species join red fescue including coastal stalwarts such as kidney vetch Anthyllis vulneraria, bird’s-foot-trefoil Lotus corniculatus, sea campion Silene uniflora, English stonecrop and of course thrift, which is better suited than red fescue grass to excessive drainage. It is perhaps this community above all others that typifies the British coast at its best in late May and early June where the cliffs are awash with colour.

MC9 Festuca rubra-Holcus lanatus maritime grassland.

With more shelter, a gentler slope and deeper, though generally free-draining, soils the Festuca rubra-Armeria maritima association gives way to a MC9 Festuca rubra-Holcus lanatus maritime grassland. Soil conditions (moisture and nutrient status) are now as important as maritime influence. Although red fescue still dominates the community has a more mesophytic (moderately moist) feel with frequent Yorkshire fog Holcus lanatus, cocksfoot grass Dactylis glomerata, white clover Trifolium repens, sorrel Rumex acetosa, ribwort plantain Plantago lanceolata and common mouse-ear Cerastium fontanum. To landward (or shelter) this community often grades into H7 Calluna vulgaris-Scilla verna maritime heath (see below).

MC11 Festuca rubra-Daucus carota ssp. gummifer maritime grassland

On calcareous sea cliffs, where rendzinas deepen to brown calcareous soils on more sheltered, gentler slopes the MC9 Festuca rubra-Holcus lanatus community tends to be replaced by the MC11 Festuca rubra-Daucus carota ssp. gummifer maritime grassland. This community is characterised by a short tussocky sward, red fescue still dominates but cocksfoot grass is now an obvious compatriot, sea carrot Daucus carota ssp. gummifer when in flower gives the cliff tops a striking appearance and this community its distinctive stamp. Sea carrot is susceptible to frost and this may explain why it tends to be restricted to the cliffs of southern Britain. Where drainage is excessive sea-kale Crambe maritima, buck’s-horn plantain P.coronopus, rock samphire Crithmum maritimum and viper’s-bugloss Echium vulgare do well, as does common restharrow Ononis repens. In this community maritime influence is muted: soil depth and drainage characteristics account for observed variation.

MC10 Festuca rubra-Plantago spp. maritime grassland

To differences accounted for by exposure and edaphic diversity those attributed to grazing pressure must be added. Some sea cliffs are open to stock (sheep and cattle) and rabbits are ubiquitous although not to pre-1950’s levels. The effect of grazing in general is to shorten and tighten the sward and to favour grazing resistant or unpalatable species. With grazing red fescue, Yorkshire fog and cocksfoot grasses usually decline in favour of ribwort, sea and buck’s-horn plantains and the resultant community is the MC10 Festuca rubra-Plantago spp. maritime grassland.

MC12 Festuca rubra-Hyacinthoides non-scripta maritime bluebell community

In areas where there is no grazing, where there are deep, moist, fertile brown soils with a moderate maritime influence, often on gentle to moderate north facing slopes, a lush carpet of red fescue, bluebells Hyacinthoides non-scripta, sorrel Rumex acetosa and Yorkshire fog grass can develop. This vegetation type is recognised as the MC12 Festuca rubra-Hyacinthoides non-scripta maritime bluebell community. It is found on most rock types but not limestone. The maritime influence keeps vigorous grasses like false oat grass Arrhenatherum elatius in check, which might otherwise out-compete the bluebells. Interestingly it is held that this community need not be a relic of once scrub/wood covered land as it occurs on sites where it is difficult to envisage woodland cover ever surviving.

Maritime heath and scrub

If some form of woodland is the climatic climax over much of the British Isles and grassland a biotic plagio-climax vegetation, then in between the two there is “scrub” which must be seen as nothing more than a successional stage, transitory between the aforementioned vegetation types. But on the coastal strip, as traditional agriculture retreats behind fences and grazing from stock animals decreases, maritime grasslands and heath, on all but the most salt-lashed areas, are being overgrown by scrub in the form of blackthorn, gorse and bramble interspersed with barcken. Here where the prevailing conditions are too extreme for trees, scrub becomes the climax vegetation in its own right.

Scrub is not without merit. It provides excellent cover for birds and invertebrates and is valuable alongside a diverse coastal mosaic of grassland types and heath. But there is a feeling that the coast is suffering from an over-dose of scrub to the detriment of other coastal habitats and biodiversity in general. Various schemes are being set up to manage the situation by controlled burning and/or cutting and/or grazing to get the amount of scrub back into balance and encourage restoration of the other coastal vegetation types.

Maritime heath

Landward of the maritime grassland communities, with salt input still significant but decreasing, a belt of maritime heath is often visible. In the NVC scheme heaths are vegetation types in which sub-shrubs play the most important structural role, sometimes in a broken or dwarfed canopy, with species such as ling Calluna vulgaris and other ericoids (heaths), various berries Vaccinium spp, crowberry Empetrum nigrum, bearberry Arctostaphylos spp, gorse Ulex minor and U. gallii the usual dominants, alone or in various combinations.

Calluna vulgaris-Scilla verna heath (H7).

he scheme recognises twenty-two types of heath community, two of which have been commonly recorded on the coast, namely H7 and H8, but the most relevant to the present discussion is the consistently maritime community Calluna vulgaris-Scilla verna heath (H7). Here salt-spray deposition is at moderate levels, soils are base-poor brown earths and rankers, sub-shrubs (ling and bell heather Erica cinerea) are few in number and rather inconspicuous, being reduced to a low, wind-shaped mat that is often patchy in exposed and rocky locations. Throughout, plants such as sheep’s fescue Festuca ovina, Yorkshire fog grass, bird’s-foot trefoil, cat’s ear Hypochoeris radicata, thyme Thymus polytrichus, ribwort plantain and tormentil Potentilla erecta are present with spring squill and sea plantain in quite rich grassy swards together with other suites of herbs as conditions vary with salt input and soil type. On exposed sea-cliffs this maritime heath probably represents the climatic climax community although grazing pressure will influence it. Salt and/or grazing pressure will prevent further successional development.

It is interesting to note how species abundances within the community respond to small-scale abiotic variations. Sea plantain favours grazed areas; cat’s-ear drier soils; glaucus sedge Carex flacca and the spring sedge C.caryophyllea free-draining, base-rich soils; carnation sedge C.panicea and common sedge C.nigra wetter, more acid ground; common dog-violet Viola riviniana and devil’s-bit scabious Succisa pratensis moist conditions and sea carrot, common milkwort Polygala vulgaris and lesser hawkbit Leontodon saxatilis drier. These variations are the key to the various sub-communities (sub-divisions of the main community types) that exist within the NVC scheme. H7 for example, has five sub-communities H7a-H7e, where H7a is the Armeria maritima sub-community. This sub-community is the most salt-tolerant of the five, ling is present as the most salt tolerant of the sub-shrubs accompanied by a good assemblage of maritime herbs. Salt input is high enough to override small differences in soil type.

The Calluna vulgaris-Ulex gallii heath (H8)

The Calluna vulgaris-Ulex gallii heath (H8) is a community found on free draining, generally acid to neutral soils in the warm oceanic regions of lowland Britain. It often merges with H7 to seaward and is limited in its salt tolerance by the sensitivity of western gorse Ulex gallii to salt spray. A coastal variant, the Scilla verna sub-community typically has more spring squill and sheep’s fescue than the other four sub-communities.

Scrub

In sheltered situations on the upper reaches of cliffs the heaths grade into bracken Pteridium aquilinum or scrub dominated patches. The main woody colonisers are gorse Ulex europaeus, which is even more salt sensitive than western gorse and favours drier, acid soils and blackthorn Prunus spinosa which does better on moister mulls.

Maritime grassland/heath/scrub grazing systems

Maritime cliff communities in the British National Vegetation Classification system