Sand Dunes

Shingle

Shingle is sediment between 2 and 200mm in size, comprised of a variety of different materials. It is globally restricted to only a few places – the UK, Japan and New Zealand are home to the large majority of shingle resources. Globally shingle coasts are found at higher latitudes where shores were subject to Pleistocene glaciation, although locally important examples of coral shingle exist.  In the UK, South coast examples are often flint based, having been eroded from chalk cliffs, while in the North and West, glacial and river depositions have fed shingle coasts. The substrate may be mixed with sandy or silt sediments due to the pattern of transport onto the beach or from nearby habitats like salt marsh or dune systems. The majority of shingle systems in the UK were formed by about 4,000 BP, geomorphological processes at the coast reworking and depositing shingle during periods of lower sea level. Around the coast of the UK, 3,500km of pure shingle exists while a total of 19,000km contains an important component of shingle.

In contrast, the extent of coastal vegetated shingle is far less, thought to total less than 6,000ha when last measured in 1991. Shingle is mobile by nature and as a result is a difficult substrate for plants to colonise. The environment is also inhospitable and the majority of vegetation observed is perennial in nature. Further inland where shingle is less mobile, closer vegetation cover is more common including successional development.

Geomorphology

Shingle beaches occur on high energy wave dominated coasts where a sediment supply is available for reworking. The beach profile tends to be relatively steep as the porous nature of shingle means backwash (the retreating wave) filters through the substrate depositing any sediment it still carries, rather than travelling over the surface and carrying more sediment away. The swash (incoming wave) action which deposits sediment is thus dominant to the backwash allowing net landward transport and creating a steeper profile. Shingle may only be found on the upper beach because the backwash is not sufficient to remove larger clasts. Shingle structures come in many different forms including spits, fringing pocket beaches, barriers and barrier islands formed by long shore drift, and cuspate forelands. Many shingle barrier systems result from Holocene marine transgression and are undergoing major change again as sea levels rise. Rising sea level tends to move shingle inland as moderate wave action pushes it to the top of the beach and major storms overtop the structure carrying ‘aprons’ of shingle over and initiating gradual rollover migration.

Fringing/pocket beach
Porlock, (Somerset) Claymoddie (Dumfries and Galloway)and Llanddulas (Clwyd).

These strips of shingle occur at the top of beaches in contact with the land and are subject to frequent inundation. They often occur underneath sedimentary cliffs, at the foot of coastal dunes or near salt marsh.

Spits
Scolt Head (Norfolk), Aber Dysinni (Gwynedd) and Whiteness Head (Highland)

These features occur when there is an abrupt change in direction of the coast away from the dominant direction of longshore drift. It is a long arm of sediment, attached to the beach at one end, which serve as a repository for sediment being carried along the current longshore drift pathway, rather than following the coastline.

(Tombolo) Barriers and bars
Slapton Sands (Devon), Cemlyn Bay (Anglesey) and Chesil (Dorset)

Are similar to spits but occur across bays and estuaries, may be attached at both ends and are often enclosing a freshwater area behind forming a lagoon.

Barrier islands
Scolt Head (Norfolk) or Culbin Bar (Highland)

Are areas of shingle deposited offshore with no attachment to the mainland and may act as a skeleton on which sand dunes can build.

Cuspate forelands
Dungeness (Kent), Rhunahaorine (Kintyre)

These are triangular shaped protrusions formed as a result of longshore drift in opposing directions. The current pathways in isolation from each other would form spits but in opposition, sediment is deposited in this pattern, pushed out to a point as waves resist each other.

Hydrology

Similarly to sand dunes, shingle features often conceal a fresh water table sitting on top of saline water. Its porous nature allows rapid infiltration of water and shingle does not retain water well, but the ‘mulching’ effect of shingle on the soil surface can help reduce evaporation (Randall, 2004). The freshwater table rises and falls twice daily as saline water comes in with the tide providing a vital water source for plants. The freshwater resource underlying shingle is of very good quality for drinking water meaning aquifers have been and continue to be used such as Dungeness. At Denge beach saline incursion prompted a limit on abstraction in 1984 when it was realised the resource was finite and in danger of being depleted. The amount of finer material such as silt and sand within the substrate determines to an extent the hydrological regime and therefore what communities can establish there.

Ecology

The main constraints on the development of vegetated shingle are the degree of mobility of the structure, its ability to retain water and the development of soil. Shingle rarely develops a true soil, although in Culbin, high rainfall has allowed the development of soil to a stage where it supports heathland scrub species. Soil development is dependent on the breakdown of organic matter so it is fortunate that pioneering species are able to withstand such inhospitable conditions. Sea kale Crambe maritima, sea pea, Lathyrus japonicus, and sea campion Silene uniflora are species which can tolerate exposure to salt spray and some degree of burial or erosion and so can even be found below the high water mark where shingle is mobile. Further up the beach where conditions are more stable and some humus has built up Babington's orache, Atriplex glabriuscula and sea beet, Beta vulgaris can establish. In the lee of the prevailing wind or on stable shingle ridges sea thrift and biting stonecrop can from a carpet of flowers and a rich lichen community can develop if shingle remains undisturbed for a long time. Scrub species only develops on the oldest, least disturbed shingle and as at Culbin and the mouth of the river Spey can develop into typical heathland species. Invertebrates are of vital importance to vegetation establishment as mites and collembolans help break down plant remains and others help pollinate. Many moth and bumble bee species are associated with the habitat, which because of its rarity affords them protection. There are many other special rare species, such as the Whelk-shell jumping spider (Pseudeuophrys obsoleta), which lives in empty whelk shells thrown up by storms.

 

http://www.buglife.org.uk/advice-and-publications/advice-on-managing-bap-habitats/coastal-vegetated-shingle


Brown-banded carder bee (Bombus humilis), Large garden bumble bee (Bombus ruderatus), Short haired bumble bee (Bombus subterraneus), and the hopper-bug Aphrodes duffieldi. Rhopalus rufus
a bug Monosynamma maritima
a leafhopper Aphrodes duffieldi
Dark guest ant (Anergates atratulus)
a Cuckoo bee Nomada ferruginata
Shrill carder bee (Bombus sylvarum)
a
Gilkicker weevil (Pachytychius haematocephalus)

Gulls, plovers and terns will nest on shingle structures but as they are ground nesting, predators such as foxes and human trampling are a significant threat to breeding. The habitat is a haven for many over wintering and migratory birds who find food in the shingle itself or associated scrubland and wetlands. Many of the UK’s sites have endemic species like the leafhopper Aphrodes duffieldi at Dungeness and the scarce Nottingham catchfly, which is the food plant of several rare moth species. On some of the less disturbed sites, grey seals haul out to rest or give birth.

Threats

Coastal vegetated shingle is subject to similar threats as sand dunes including pressures from human use, coastal squeeze inhibiting its ability to naturally migrate and interruption to the sediment supply. The vegetation on this habitat does not form stabilising mats or grasslands as readily as it does on sand dunes meaning shingle habitat can be destroyed more quickly by erosive processes and general disturbance. However, because sandy beaches are generally preferred to shingle for recreation the pressure may be less than on sandy shores. The plant and animal communities which have colonised shingle have generally done so where mobility of the shingle is low meaning that any physical disturbance of the sediment is poorly tolerated. Vehicular use on shingle whether by the military or other users is particularly problematic for shingle habitats and there are examples of vehicle tracks on shingle ridges at Dungeness which will remain indefinitely. Where access is totally or partially controlled, vegetation and invertebrates have been shown to increase while a lack of access is particularly helpful to ground nesting birds whose eggs are virtually camouflaged on the shingle.

Any kind of development on shingle is likely to negatively affect it by reducing its ability to migrate in response to the sea and directly by reducing the area available for colonisation. Water abstraction, nuclear power plants, housing and defence are all examples of development which occur on the habitat. Although this kind of development has stopped, many shingle sites are already damaged and rehabilitation efforts are limited while the structures remain. The morphology of the shingle ridge may have been altered  by building and sea defence works to protect the infrastructure further inhibits its ability to behave naturally. Water abstraction at Dungeness has been limited but there is still evidence of drought stress on the vegetation.

A reliable sediment supply is perhaps the most important factor in sustaining a shingle resource as without sediment to pick up and deposit on the beach, the sea would simply erode shingle structures. The supply may not be continuous and storm events deposit the greatest volumes of shingle onto the shore. Shingle features constantly change morphologically as their finite sediment supply is reworked landward and alongshore. The sediment supply is compromised when it is extracted for aggregates, restricted by coastal defence structures or artificially redistributed around the site. Now that there is more knowledge about coastal sediment cells, coastal squeeze and managed realignment attempts are being made to rectify these problems. One method involves mechanical beach re-profiling, which is unlikely to solve the problem as it does not address the issue of supply. In the long term shingle structures need to be able to respond to periodic storms, changes in sea level, wave regime or currents which it cannot do if its movement is restricted by sea defence structures. Natural long shore drift is prevented by groynes while sea defence walls behind a feature stop shingle ridges rolling back landwards. 

Coastal vegetated shingle is very rare and invites protection at a number of levels. Firstly it is recognised under an EU habitat type ‘Perennial vegetation of stony banks’ with a few sites consequently being proposed SACs and some trying to become SPAs under the EC bird directive. European funding is available and at Orfordness, a Life project has allowed large scale management tasks to take place including control of access and experimental ridge recreation. The majority of sites have been designated SSSIs/ASSIs and many are also declared as LNRs/NNRs meaning statutory or local management bodies are involved. The new generation of shoreline management plans will reflect the government’s commitment to protecting coastal habitats and outline ways in which sites with shingle can allow it to respond to sea level rise in future. There is far greater knowledge of geomorphology in coastal management today and the use of coastal sediment cells will be useful in understanding how shingle structures can function as sea defences most effectively. In the past, we have always prioritised human activity over nature but slowly as we realise this is unsustainable there may be a reprieve for shingle habitats.

One of the biggest problems involved in protecting coastal vegetated shingle sites is the difficulty in accurately mapping and monitoring the habitat. Most approximations of the size of the resource are based on a survey from 1994. More recently Natural England commissioned a new survey which took advantage of newer technologies and allows the information to be conveyed in GIS. Still, the problem of determining habitat boundaries remains as shingle structures are often found in transitional zones bordering sand dunes and salt marsh. Where vegetation cover percentage is high, this is even more difficult. The mobile nature of shingle structures mean they are constantly evolving and changing position making comparisons over different timescales troublesome.

http://jncc.defra.gov.uk/pdf/csm_coastal_shingle.pdf

Common Standards Monitoring Guidance for Vegetated Coastal Shingle Habitats. Version August 2004

Action Plan for coastal vegetated shingle available at http://jncc.defra.gov.uk/page-5155 

Doody, P., and Mitchell R., 1982. The conservation of coastal shingle features.  Nature Conservancy Council.

Haslett, S. K., 2000. Coastal Systems. Routledge, London.

Woodroffe, C. D., 2002. Coasts Form, process and evolution. Cambridge University Press, Cambridge.