Threats to UK Coastal Habitats

 

UK coastal habitats and their associated species are threatened by a range of factors. The coastline has been subject to urban development, land-claim for agriculture and industry, recreational pressure, and changing agricultural use. Conservation designations, improved site management and planning policies have reduced some of these threats, but port and other transport developments remain issues. An increasingly important issue, especially on soft coasts, is 'coastal squeeze', i.e. where the extent of saltmarsh is diminishing as it is 'squeezed' between flood defences and rising relative sea levels.

 

The table below provides a summary of major pressures and threats to UK coastal habitats – details are given beneath. These are based on information in the 3rd UK Report on Implementation of the Habitats Directive, the UK Biodiversity Habitat Action Plans, and Common Standards Monitoring for Designated Sites: First Six Year Report.

 

 

Sand dunes

Saltmarsh

Vegetated shingle

Maritime cliff and slopes

Machair

Changing agricultural practice, including grazing

*

*

*

*

*

Sediment supply/dynamics

*

*

*

 

 

Recreation

*

 

*

 

 

Coastal protection, including afforestation

*

 

 

*

 

Infestation by Phomopsis juniperovora

*

 

 

 

 

Air pollution

*

 

 

 

 

Falling water tables

*

 

 

 

 

Erosion and ‘coastal squeeze’

 

*

 

*

 

Development, extraction and other land claim

 

*

*

 

 

Cord grass Spartina anglica invasion

 

*

 

 

 

Social change in crofting

 

 

 

 

*

 

Sand Dunes

 

Sediment supply

Unless artificially constrained, the seaward edges of sand dunes can be a highly mobile feature, though there is a natural trend to greater stability further inland. Very few dune systems are in overall equilibrium, and a majority of those in the UK demonstrate net erosion rather than net progradation; insufficient sand supply is frequently the underlying cause.

 

Beach huts encroaching onto sand dunes © JNCC

Coastal protection/afforestation

Many dune systems are affected by sea defence works or artificial stabilisation measures, such as sand fencing, marram planting or afforestation to conifers. Such defence systems usually reduce the biodiversity inherent in the natural dynamism of dune systems, and may cause sediment starvation down-drift. UK dunes as a whole suffer from over-stabilisation and poor representation of the mobile phases. A few dune systems have been largely transformed to conifer plantations, beneath which the dune vegetation is suppressed and the water table lowered.

 

Recreation and beach management

Sand dunes are used heavily for recreational purposes. Moderate pressure by pedestrians may cause little damage, and may even help to counteract the effects of abandonment of grazing, but excessive use, and vehicular use in particular, causes unacceptable erosion. On some heavily used beaches the formation of embryo dunes is inhibited by beach cleaning using mechanical methods, which impedes the seaward accretion of dune systems.

 

Changes to agricultural practice – grazing

Grazing is normally necessary to maintain the typical fixed dune communities, but over-grazing, particularly when combined with the provision of imported feedstuffs, can have damaging effects. A more widespread problem is under-grazing, leading to invasion by coarse grasses and scrub, though rabbits are locally effective in maintaining a short turf.

 

Air pollution

Atmospheric nutrient deposition is considered to be a factor adversely affecting sand dunes. It is also suspected that nutrient deposition on many sand dunes is already above their critical threshold for impacts on vegetation. For dune slacks, this could lead to a speeded up succession away from dune slack vegetation. For further info: UK Air Pollution Information System (APIS). 

 

Restoration of dune slack vegetation at Dawlish Warren NNR, Devon - bramble scrub has been cutback to allow species-rich herbaceous vegetation to florish © JNCCFalling water tables

Dune slacks support characteristic communities dependent on a seasonally high water table, including the formation of temporary or even permanent ponds. In some dune systems with important slacks, a long-term fall in the water table has led to loss of the specialist slack flora and invasion by coarse vegetation and scrub. The causes are believed to be local extraction of water and/or drainage of adjacent land used for agriculture or housing.

 

Infestation by Phomopsis juniperovora

Dunes with Juniper is a habitat found only on two sites in Scotland. Junipers are vulnerable to infestation by pathogenic fungi, especially juniper blight (Phomopsis juniperovora), which infect the new growth, which gradually dies, leading to the loss of the habitat.

 

Saltmarsh

 

Erosion and 'coastal squeeze'

Erosion of the seaward edge of saltmarsh occurs widely in the high energy locations of the larger estuaries as a result of coastal processes. There is evidence that this process is exacerbated both by the isostatic tilting of Britain towards the south-east, and by climatic change leading to a relative rise in sea level and to increased storminess. Many areas of saltmarsh are being 'squeezed' between an eroding seaward edge and fixed flood defence walls.

 

Sediment dynamics

Local sediment budgets may be affected by coast protection works, or by changes in estuary morphology caused by land claim, dredging of shipping channels and the impacts of flood defence works over the years.

 

Spartina anglica (bright green) invading Salicornia beds, Strangford Lough, Northern Ireland © Paul CorbettCommon Cord-Grass invasion

The common cord-grass, Spartina anglica, readily colonises mudflats and has spread around the coast - see photo. The development and spread of Spartina anglica has had most impact on the pioneer communities of saltmarsh, especially on Salicornia communities. As a result, attempts have been made to control it at several locations, although in some areas it is undergoing dieback for reasons not fully understood.

 

Land claim

Large-scale saltmarsh land claim schemes for agriculture are now rare. However, smaller-scale land claim for industry, port facilities, transport infrastructure and waste disposal is still comparatively common, and marina development on saltmarsh sites occurs occasionally. Such developments usually affect the more botanically diverse upper marsh and landward transition zones.

 

Changes to agricultural practice – grazing

In recent decades, some grazed saltmarshes have been abandoned, leading to domination of the mid to upper marsh by rank grasses. Intensive grazing is considered to be a problem in some areas: grazing has a marked effect on the structure and composition of the vegetation by reducing the height of the vegetation and the diversity of plant and invertebrate species, but creates a sward attractive to wintering and passage wildfowl and waders. Less intense grazing produces a tussocky structure which favours breeding waders. Traditionally ungrazed saltmarshes should remain so.

 

Vegetated shingle

Drift line vegetation depends on a continued supply of sediment - Strangford Lough, Northern Ireland © Paul Corbett

 

Sediment supply and dynamics

The health and ongoing development of a shingle feature depend on a continuing supply of shingle. This may occur sporadically as a response to storm events rather than continuously. It is frequently lacking owing to interruption of coastal processes by coast defence structures, by offshore aggregate extraction, or by artificial re-distribution of material within the site. Attempts have been made to rectify the situation by beach recharge or by mechanical re-profiling – which is likely to fail in the long run because it does not address the lack of new material. Shingle features are rarely stable in the long term. Many structures exhibit continuous longshore drift and ridges lying parallel to the shoreline tend to be rolled over towards the land by wave action in storm events. This movement has a knock-on effect on low-lying habitats behind the shingle. Movement is likely to be accelerated by climate change resulting in sea level rise and increased storminess.

 

Extraction and development

Shingle structures have been subject to varying degrees of extraction resulting in severe alteration of morphology and vegetation or almost total destruction of major parts of the feature. Industrial plant, defence infrastructure and even housing have been built on shingle structures, destroying vegetation and ridge morphology.

 

Recreation

Shingle vegetation is fragile and the wear and tear caused by access on foot, and particularly by vehicles, has damaged many sites. The causes include military use, vehicle access to beaches by fishermen, and recreational use. Such disturbance can also affect breeding birds.

 

Changes to agricultural practice – grazing

In a few cases areas of shingle were traditionally grazed, but this management has now largely ceased, leading to domination by willow carr on wetlands and changes to vegetation structure. The impacts of removal of grazing on breeding birds and other shingle species are not fully understood.

 

Maritime cliff and slopes

 

Coastal cliff grassland being restored at Hope's Nose, Torbay, Devon - thorny scrub has been cleared and sheep grazing re-instated © JNCCErosion

This is a highly significant factor in soft cliffs. High rates of erosion do not imply a loss of the cliff resource, either in geological or biological terms. Cliff face communities are able to retreat with the cliff line, and erosion is vital for constantly renewing geological exposures and recycling the botanical succession on soft cliffs. However, cliff-top vegetation may be destroyed where it is squeezed between a receding cliff face and cultivated land.

 

Coastal protection

Protective systems have been built on many soft cliff coasts in order to slow or stop the rate of erosion and thus protect capital assets behind the cliff line. Such works have the effect of stabilising the cliff face, resulting in geological exposures being obscured, bare soil and early pioneer stages being progressively overgrown, and wet flushes drying out. Soft cliffs require a certain amount of natural erosion to maintain their interest, but unprotected soft cliff is now a relatively scarce habitat.

 

Changes to agricultural practice

Post-war intensification of agriculture has led to maritime grassland on more level terrain being ploughed out, while that on sloping ground has been abandoned and, where not maintained by exposure, is frequently overgrown by scrub. In traditional low-intensity grazing systems, livestock were grazed on cliff grasslands where they maintained open maritime grassland vegetation.

 

Machair

 

Changes to agricultural practices

This has resulted in an overall loss of arable biodiversity through loss of species number and abundance, with apparent similar declines in the associated fallow that is a feature of the normal machair rotational management system. The practice of cutting grass for silage rather than hay reduces seeding by flowering plants and destroys the nests of characteristic birds such as the corncrake. Improvement of machair grassland – usually done by re-seeding, drainage and stock feeding – reduces sward species diversity as well as habitat diversity over a wider area. The application of herbicides on crops and the use of modern ploughs both appear to be direct causes of species loss. Under-grazing and more generally poor management of seasonal grazing allow species-poor grassland to develop. Over-grazing is a problem on some areas of machair, preventing plants from setting seed. On some sites it has disrupted geomorphological processes, such as blowouts.

 

Social change in crofting

Such change has resulted in heavy, all-year grazing of machair grasslands as part of a switch from arable to stock grazing, and from cattle to sheep as predominant stock. This has reduced sward species diversity and the ability of plants to flower and set seed. It has also reduced cover for breeding birds.