Habitat account - Coastal sand dunes and continental dunes


2150 Atlantic decalcified fixed dunes (Calluno-Ulicetea * Priority feature

Background to selection

Distribution of SACs/SCIs/cSACs with habitat 2150 Atlantic decalcified fixed dunes (Calluno-Ulicetea).  Click image for enlarged map.
Distribution of SACs/SCIs/cSACs with habitat 2150 Atlantic decalcified fixed dunes (Calluno-Ulicetea). Click image for enlarged map.

Description and ecological characteristics

 

This habitat type occurs on mature, stable dunes where the initial calcium carbonate content of the dune sand is low. The surface soil layers rapidly lose their remaining calcium carbonate through leaching, and become acidified. The Annex I types Atlantic decalcified fixed dunes (Calluno-Ulicetea) and 2140 Decalcified fixed dunes with Empetrum nigrum are similar in composition. Within the UK Decalcified fixed dunes with Empetrum nigrum has a more restricted distribution, being confined to Scotland, in relatively wetter and more base-poor conditions. Atlantic decalcified fixed dunes is more widespread, tolerating drier and warmer conditions. At some Scottish sites it is difficult to distinguish between these two Annex I habitat types, as the vegetation forms a continuous spectrum of variation within complex habitat mosaics. Indeed, they may succeed one another at the same location over time.

 

The most characteristic community is dune heath in which heather Calluna vulgaris is found in combination with sand sedge Carex arenaria. The main species present vary considerably throughout the UK. Bell heather Erica cinerea is abundant in dune heath on west coast sites, but much scarcer in the east, where heather Calluna vulgaris predominates. Associated with the heathland in drier conditions, and forming transitions with it, is acidic dune grassland. This is often a precursor to heath development and in these drier conditions is usually characterised by a combination of the fine-leaved grasses such as sheep’s-fescue Festuca ovina and common bent Agrostis capillaris, with sand sedge Carex arenaria. On very nutrient-poor sand that is also subject to severe drought the heath tends to be dominated by lichens, which form a continuous grey carpet over the ground. In the UK this Annex I type corresponds to the following NVC types:

 

     

  • H1d  Calluna vulgaris – Festuca ovina heath, Carex arenaria sub-community
  • H11a  Calluna vulgaris – Carex arenaria heath, Erica cinerea sub-community
  • H11c  Calluna vulgaris – Carex arenaria heath, species-poor sub-community

 

Other dry heath types occurring on coastal sand dunes may also be referable to this Annex I type.

 

Grey hair-grass Corynephorus canescens is a prominent feature of the small number of fixed, decalcified dune systems in eastern England. This species is more typical of the dry acidic dunes of the Baltic and 2330 Inland dunes with open Corynephorus and Agrostis grasslands, and represents an interesting outlier in the UK of a dune type much more widespread on the continent.

 

At most sites at which Atlantic decalcified fixed dunes (Calluno-Ulicetea) vegetation occurs, it forms a mosaic with other Annex I habitat types. Fixed dune vegetation tends to occur on the larger dune systems, which have the width to allow it to develop.

European status and distribution

 

Atlantic decalcified fixed dunes (Calluno-Ulicetea) are widespread in Europe, and the UK lies at the centre of the north – south range of this habitat type.

UK status and distribution Click to view UK distribution of this habitat

 

Atlantic decalcified fixed dunes (Calluno-Ulicetea) are well represented in the UK and there is considerable variation in the vegetation of this habitat type, both between northern and southern sites and between sites on the east and west coasts. A large proportion of the area of the national resource occurs on a relatively small number of sites, the largest of which (Morrich More) is in Scotland.

Site selection rationale

 

Sites have been selected to represent the ecological variability and geographic range of this habitat type. Sites selected tend to be the largest examples, in which substantial areas of dune heath occur in a mosaic of dune habitats. These sites are the least-modified and tend to be inherently stable in terms of structure and function. A relatively small number of sites, supporting a large proportion of the total national resource, has been included in the SAC series.


Site accounts

Barry Links Eastern Scotland
Barry Links is a large site on the east coast of Scotland and has a relatively extensive area of Atlantic decalcified fixed dunes (Calluno-Ulicetea). The dunes are part of a full successional transition from embryonic foredune to heath on fixed dune. There is a complex of dune grassland on Atlantic decalcified fixed dunes. The pattern of development of Calluna heath suggests that decalcification has occurred through leaching of the sand over an extended period of time. This is in contrast to most other sites with extensive dune heath. Usually these sites are composed of sand with an extremely low initial calcium carbonate content, and decalcification is a relatively rapid process. In addition there are transitions to wet heath, which in turn grades into dune slack.
Dornoch Firth and Morrich More Extra-Regio, Highlands and Islands
Dornoch Firth and Morrich More represents Atlantic decalcified fixed dunes (Calluno-Ulicetea) in north-east Scotland, with dune heath containing heather Calluna vulgaris and sand sedge Carex arenaria. At this site, dune vegetation has developed on a coastline that has been generally rising relative to sea level in the 7,000 years since the last glaciation. A combination of leaching, stabilisation and the decreased influence of saltwater has produced a sequence of dry, stable dune ridges, interspersed with wet dune hollows. The Atlantic decalcified fixed dunes vegetation covers a large area on this site and forms part of a complex mosaic of fixed dune vegetation types, principally 2140 Decalcified fixed dunes with Empetrum nigrum, together with saltmarsh and transitional communities that include large populations of several northern dune species, such as Baltic rush Juncus balticus. This is the most important acidic dune site in Scotland, owing to its size and the exceptional diversity of habitats within it. Despite some localised industrial development, structure and function are well-conserved at this site and accretion is continuing.
Dorset Heaths (Purbeck and Wareham) and Studland Dunes Dorset and Somerset
Studland Dunes comprises the only large dune heath site in the south and south-west of Britain. The heathland occupies a series of dune ridges, which have developed over a period of several hundred years. The development of these ridges was the subject of a classic study (Diver 1933) and the processes are still active today. Structure and function of the dune heath communities are therefore well-conserved. The dry open heath is an important habitat for rare reptiles such as sand lizard Lacerta agilis. At the western margin of the dune ridges the dry dune heath grades into wet heath in which cross-leaved heath Erica tetralix is prominent, while at the northern end it grades into the southern heathland types of inland Dorset.
Drigg Coast Cumbria
Drigg represents Atlantic decalcified fixed dunes (Calluno-Ulicetea) in north-west England. There are substantial areas of the habitat type, showing a wide range of ecological variation. Some areas are dominated by heather Calluna vulgaris and bell heather Erica cinerea. Within the dry dune heath are wetter areas in which cross-leaved heath Erica tetralix is prominent. There are large areas of acidic dune grassland with a prominent lichen component and also areas where sand sedge Carex arenaria grows in carpets of the moss Racomitrium canescens.
Invernaver Highlands and Islands
This very exposed and active dune system is an extensive representative of Atlantic decalcified fixed dunes (Calluno-Ulicetea) on the north coast of Scotland and is an extreme northern variant of the habitat type. Areas of sand have been blown up and over cliffs by strong winds to form ‘climbing dunes’. This situation is functionally similar to the blown sand of Penhale Dunes, although the communities present are very different because of climate and location. These dunes support a highly complex mosaic of fixed dune grassland and heathland communities. Atlantic decalcified fixed dunes exist in a matrix of other dune heath communities that include a number of arctic-alpine species. This is the largest example of an extreme northern variant of this vegetation type and is of interest because it forms a transition between the typical northern acidic dune heath vegetation and the arctic vegetation that is widespread further north. It is therefore considered to be particularly important in the European range of ecological variation of dune vegetation.
Luce Bay and Sands Extra-Regio, South Western Scotland
Torrs Warren – Luce Sands is the largest acidic dune system in south-west Scotland and supports extensive areas of Atlantic decalcified fixed dunes (Calluno-Ulicetea). It contains a variety of dune landforms and therefore a complex mosaic of dune habitats. Atlantic decalcified fixed dunes dominated by heather Calluna vulgaris is extensive and occupies the drier dune areas. The dunes are relatively undisturbed and are more or less free from grazing by domestic livestock, resulting in relatively stable vegetation communities.
Murlough Extra-Regio, Northern Ireland
Murlough is the largest and most important dune heath site in Northern Ireland. The site is an old dune system with acidic sands and a long history of traditional management. The vegetation is dominated by heather Calluna vulgaris and bell heather Erica cinerea, with some areas of acidic dune grassland and other areas dominated by mosses and an abundance of lichens. These areas of heath grade into 2130 Fixed dunes with herbaceous vegetation (“grey dunes”) and gorse scrub.
Winterton - Horsey Dunes East Anglia
Winterton – Horsey Dunes is the only significant area of dune heath on the east coast of England and also includes areas of acidic dune grassland as an associated acidic habitat. The contrast with the nearby calcareous and species-rich dunes of north Norfolk is marked. The Atlantic decalcified fixed dunes (Calluno-Ulicetea) vegetation is characteristic of dune heath in an eastern locality with low rainfall. The drought-resistant grey hair-grass Corynephorus canescens is a characteristic species of the open dry dune soils.

SACs/SCIs/cSACs where this Annex I habitat is a qualifying feature, but not a primary reason for site selection

Morecambe Bay Cumbria, Extra-Regio, Lancashire
Sefton Coast Merseyside
 

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