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BIODIVERSITY REFERENCE
 
British habitats
 
   Lowland Heathlands   
 
(page 2)


COASTAL HEATHLANDS

Some of our most attractive heaths are on the western sea-cliffs, a blaze of colour when the heathers and Ulex gallii are in flower in late summer. U. gallii (Western Gorse) is a typical component of these heaths, notably NVC communities H4 and H8 (see previous page), but sometimes becomes a nuisance when it produces a very solid, prickly mass of vegetation that allows the plants and invertebrates of open conditions to survive only along the sides of increasingly narrow and trampled pathways. However, Ulex species also add nitrogen to the soils, as they possess root nodules containing nitrogen-fixing bacteria.
Dwarfed and prostrate ecotypes of a number of plant species have developed in the exposed conditions.

 
Cliff-top heathland in the south-west, dominated by Calluna vulgaris and Erica cinerea, with Western Gorse (Ulex gallii) (not yet flowering here) and scattered bushes of Common Gorse (U. europaeus). Photograph: Porthtowan, Cornwall, July 2000.
 


 
Ulex gallii and Erica cinerea in south-western coastal heath. Photograph: above Wicca Pool, Cornwall, July 2000.
 


 
Coastal heathland in the north-west. Calluna and Erica cinerea dominate a fragmented heath / grass mosaic on outcrops of Lewisian Gneiss. Patchy birch scrub (Betula pubescens) is established in the deeper, damper hollows. Photograph: near Lochinver, West Sutherland, August 2001.
 


 
Dune heathland - Calluna and Erica cinerea are locally dominant on the leached sand-hills. In the foreground is a base-poor slack that has been colonised by Birch (Betula pubescens). Photograph: Torrs Warren military range, Wigtownshire, September 1993.
 

On dune systems where there is little calcium from shell-sand, or where the sand-hills become severely leached, dune heath develops, dominated usually by Calluna but sometimes with Empetrum nigrum as a major colonist. Where there remains open, bare ground within the heaths, there may also be colonisation by lichens, especially grey-coloured lichens of the genus Cladonia, and the whole dune becomes "grey dune". These same lichens also characterise the degenerative phase of heather growth, when die-back of old heather exposes the sand, while the dead stems of the heather itself are colonised by another grey-coloured lichen, Hypogymnia physodes. It should be noted that the term "grey dune" specifically relates to lichen-rich dune – in recent times it has been subject to a degree of misapplication.

Erica cinerea (Bell Heather) is typically present in these grey-dune areas and the vegetation type is commonly the 'Calluna vulgaris-Carex arenaria heath, Erica cinerea subcommunity' (variant of H11) of the NVC.

It should be noted that many of the lichens themselves do not require base-poor conditions, but in practice it is mostly the acid, heathland areas that provide the stable but open habitat for colonisation.


 

DAMP HEATHS

There is no clear distinction between heaths and mires, and mires (wet, peat-producing ecosystems) commonly occur within heathland complexes. Notably, areas of water seepage in very shallow valleys can develop into valley mires and where more water can accumulate, bog-pool complexes can form.

 
Valley bog within heathland complex. The foreground is dominated by White Beak-sedge (Rhynchospora alba). Photograph: Rosenannon Downs, Cornwall, July 2000.
 

Clearly drainage is a key factor here, and wet heaths and mires can develop when there are layers of clay within sandy strata or when iron oxide is deposited in the B-horizons of podsols to form impermeable iron-pans.

Exposure of the Bagshot Sands, Dorset, showing a clay layer within the strata.

As already stated, the typical dominant of damp heath is Erica tetralix (Cross-leaved Heath), though Calluna is often equally abundant, along with Molinia caerulea subsp. caerulea (Purple Moor-grass). Tight carpets of Sphagnum (bog-moss) species, notably S. compactum and S. tenellum may cover the peat surface (these are not hummock-forming species that would produce more rapid peat development).

Carnivorous plants are often present, supplementing their nutrition by trapping insects and other invertebrates. All three British Drosera (Sundew) species occur on wet heaths, sometimes together, though the species that is most restricted to wet heaths as distinct from other mires is D. intermedia (Oblong-leaved Sundew). Both surviving British Pinguicula (Butterwort) species can also occur - P. lusitanica (Pale Butterwort) often grows with Drosera intermedia on the western heaths.

Wetter areas may contain conspicuous patches of Rhynchospora alba (White Beak-sedge), Narthecium ossifragum (Bog Asphodel) and Sphagnum auriculatum. Nationally rare and scarce species may include Erica ciliaris (Dorset Heath), Lycopodiella inundata (Marsh Clubmoss), Hammarbya paludosa (Bog Orchid), Gentiana pneumonanthe (Marsh Gentian) and Brown Beak-sedge (Rhynchospora fusca). All of these are on the Dorset heaths.

Oblong-leaved Sundew (Drosera intermedia) is a characteristic carnivorous plant of wet heaths in the south of England, becoming much more local and mainly coastal further north. Here it is growing with Molinia caerulea (the grass) and Sphagnum (looks like S. compactum).
Photograph: Rosenannon Downs, Cornwall, 2000.


 
Dorset Heath (Erica ciliaris) is a species of south-west Europe that just reaches Britain as a nationally rare native in Dorset and Cornwall (plus one site in western Ireland, also a rare introduction elsewhere). Primarily it is a plant of the damper heaths and through habitat destruction it is now lost from a number of sites. It is a 'near threatened' Red Data book species (Rose in Wigginton, 1999). Photograph: Cornwall, 2000.
 


 

CYCLIC PROCESSES

Even when there is no development or succession to another vegetation type, heathland remains in a state of constant change. Open ground may be colonised by Calluna, but as it establishes it creates a microclimate for other plants and other organisms. Mosses such as Hypnum jutlandicum may establish an underlayer beneath the now maturing Calluna. However, as the Calluna continues to age, it begins to die off in the centre, even though younger branches may root around the periphery. Lichens such as Cladonia may now be able to colonise the exposed, drying surface of the ground. Eventually, the renewed Calluna growth from the newly established plants will replace the lichens and the sequence begins again.

Community structure may, therefore be cyclic. Such cyclic processes have been recognised in a number of different vegetation types, including climax forests, though it must also be admitted that some claimed cycles have proved to be somewhat speculative. They are well known, however, in heathland and tundra dwarf-shrub communities. Basically, pioneer, building, mature and degenerative phases can be recognised in Calluna and other dwarf shrubs, and during the degenerative phase, invasion by other species can occur. These species, even if perennial and competitive, then may also go through the same sequence of phases.

A classic such cycle is that involving alternation of Calluna and Pteridium aquilinum (Bracken), each replacing the other in its degenerative phase, a cycle described by the ecologist A.S. Watt from his long-term studies of the Breckland heaths.

 
Grass / bracken / heather mosaic in dune heathland. Here the bracken (Pteridium aquilinum) apparently is still in invasive, pioneer phase and it is probably too early to predict cycles. Photograph: Torrs Warren military range, Wigtownshire, September 1993.
 

Heath management may, however, be to stabilise vegetation in one phase, or at least to short-cut the sequence. The aim of rotational burning of grouse-moors is to clear the old, 'leggy' heather and create conditions for more rapid renewal of young heather. This maintains the heather as the dominant and provides swards of young heather shoots as food for the grouse.


 

ANIMAL LIFE

As mentioned above, heaths may be managed quite specifically for one bird, the Red Grouse (Lagopus lagopus), though the majority of grouse-moors are on higher ground or on blanket bogs. Heaths are important for other bird species, such as the Stonechat (Saxicola torquata), which is relatively frequent where there is plentiful gorse, while one of the great rarities of the southern heaths is the Dartford Warbler (Sylvia undata). The Hobby (Falco subbuteo) is a small, fast-flying bird of prey that favours heathlands; it is able to take even swallows on the wing.

Heaths, however, are most notable and valuable for reptiles, with all British reptile species occurring on the southern heaths, most particularly in Dorset. Reptiles, being cold-blooded, need to bask to raise their body heat and heaths provide the open conditions allowing them to do that.

So perhaps it is not surprising that the most characteristic vertebrate predator of heaths is a snake, the Adder (Vipera berus), our only venomous species. Bare sunny hollows on heathy banks are always liable to be occupied by a sleeping adder (often several on one bank) and a freshly woken adder is often at its most belligerent! In view of their superb camouflage this is a hazard that must always be borne in mind by any visitor to the heaths - the present author has walked within a metre of a sleeping adder, not seeing it until afterwards, on a number of occasions.

When the adder is awake and on the move it is a beautifully adapted predator, fast, silent and deadly to the small mammals, lizards and young birds which form its main prey. It is protected by law from being injured or killed by man.

 
Adder (Vipera berus), not-quite-asleep on a bare bank in dune heathland. Photograph: Torrs Warren, Wigtownshire, 1993.
 


Very much rarer and now endangered by loss of habitat is the Smooth Snake (Coronella austriaca), now with its stronghold on the remaining heaths of south Dorset. It is not venomous, feeding on slow-worms and other lizards, young birds and also insects. It is fully protected by law (Wildlife & Countryside Act, 1981), though one of its principle prey species is also endangered and legally protected, i.e. the Sand Lizard (Lacerta agilis). The latter has its stronghold on the same heaths, though it occurs a little more widely and is still in one area of coastal heaths (see link below).

Heaths are also noted for their spiders. The funnel-like webs of Aglena labyrinthica may be conspicuous on the southern heaths, but on a sunny day the Wolf Spiders (family Lycosidae) attract most attention. They are active, mobile hunters, favouring open ground, and while they are not at all confined to heathlands, they can occur on them in surprising abundance. Arguably "the" special heathland spider is the Ladybird Spider (Eresus sandaliatus), so named as the male has a bright red abdomen with black spots. It is an extreme rarity, known with certainty only at one site in Dorset, and it is a protected species under the Wildlife & Countryside Act.


Aglena labyrinthica is a sheet-web spider that is frequent on the southern heaths, spinning its characteristically funnel-shaped webs amongst low vegetation.
Photograph: Rosenannon Downs, Cornwall, 2000.


Silver-studded Blue (Plebejus argus), a butterfly now largely confined to the southern heaths. Only the male is blue.
Images: adapted from Morris (1870), plate LXI.

The Silver-studded Blue (Plebejus argus) is a butterfly that once had a wide distribution in England and Wales, but its strongholds today are the heaths of southern England, notably Dorset, the New Forest and western Surrey (Heath et al., 1984). Elsewhere its colonies are more isolated, now mostly coastal and again mostly on heathland (a separate ecological race on chalk and limestone perhaps now restricted to one site). The foodplants include gorses, heathers and Bird's Foot-Trefoil (Lotus corniculatus) and the caterpillar, like a number of other species of Blue, is tended by ants. Its decline is evidently through habitat destruction.

Morris (1870) wrote of this species:

"It is a very pretty and interesting, though rather plain species; and pleasant it is to watch it as it wanders about to "bid good-morrow to the flowers," in the height of summer, when you are glad to lie down on some grassy bank and gaze upon the plants or the insects that surround you, listening the while to the murmur of the tinkling rill, or it may be the gentle rippling of the tide over the pebbled beach, every site and every sound full of present and inexpressible enjoyment, and recalling perhaps also other times and other scenes and passages connected with them, which, alas! cannot be otherwise be recalled than by the memory, too retentive, and yet not retentive enough."
It is not clear if this was intended as a warning!


 

CONSERVATION

It will be apparent that heathlands are always vulnerable. In many cases they appear to have been initiated by human activity and their nature has depended on continued management, but farming changes have seen the end of many traditional practices. By and large, the "village poor" no longer need their common land, grazing practices change and heaths are abandoned to gorse scrub and birch woodland, or they have been ploughed, limed, fertilised and converted to arable (many such losses quite recently in Dorset and Cornwall). Wetter heaths have been drained and large areas have been turned into commercial conifer plantations. It has even been known for important sites to be damaged by well-meaning but fundamentally ignorant 'conservationists' planting trees!

While losses have been serious and unique sites are gone forever, greater awareness of their importance means that a good range of sites now have some form of conservation protection from statutory and voluntary bodies. Nevertheless, their legal protection is often tenuous and in drought years, fires can wreak great damage. Heaths are now so fragmented that such damage may not be followed by reestablishment of the rarer species from adjacent areas.

Lowland heaths are a habitat specifically included in the UK Biodiversity Action Plan (see link below).


 

References:

  • Burnett, J.H., (1964). The vegetation of Scotland, Oliver & Boyd, Edinburgh.
  • Gimmingham, C.H., (1972). Ecology of heathlands, Chapman and Hall, London.
  • Heath, J., Pollard, E., & Thomas, J., (1984). Atlas of butterflies in Britain and Ireland, Viking, Harmondsworth.
  • Morris, F.O., (1870). A history of British butterflies, 3rd ed., Bell and Daldy, London.
  • Ratcliffe, D.A. (ed.), (1977). A nature conservation review, 2 vols., Cambridge Univ. Press, Cambridge.
  • Rodwell, J.S., et al. (1991). British plant communities, 2: Mires and heaths, Cambridge Univ. Press, Cambridge.
  • Tansley, A.G., (1939). The British Islands and their vegetation, Cambridge Univ. Press, Cambridge.
  • Wigginton, M.J., (1999). British Red Data Books. 1. Vascular plants, 3rd ed., JNCC, Peterborough.


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© A.J. Silverside
e-mail: alan.silverside@uws.ac.uk
Page first hosted at www-biol.paisley.ac.uk/bioref/, November 2001; transferred, with minor edits, to lastdragon.org September 2009
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