Maritime cliffs and slopes
What is it?
Maritime cliffs and slopes comprise sloping to vertical faces on the coastline where a break in slope is formed by slippage and/or coastal erosion. There appears to be no generally accepted definition of the minimum height or angle of slope which constitutes a cliff, but the zone defined as cliff-top should extend landward to at least the limit of salt spray deposition, which in some exposed situations may reach up to 500m inland.
This definition may therefore encompass entire islands or headlands, depending on their size. On the seaward side, the area exends to include the splash zone and lichens and other species occupying this habitat.
Approximately 4000km of the UK coastline has been classified as cliff.
Cliff form is determined by geology and geological structure, together with environmental history (past and present marine erosion and glacial processes). While most maritime cliffs have been formed by coastal erosion, steep slopes falling to the sea in mountainous districts may have been formed long before the sea level reached its present position. In such cases, only the lower part of the slope will have been steepened by the sea.
Most cliff types can be classified as either ‘hard cliffs’ or ‘soft cliffs’. However, there are some intermediate types.
Hard cliffs are vertical or steeply sloping and are inclined to support few higher plants other than on ledges and in crevices or where a break in slope allows soil to accumulate. They tend to be formed of rocks resistant to weathering, such as granite, sandstone or limestone, but they can also be formed of softer rocks such as chalk, which may erode to a vertical profile.
Soft cliffs are formed in less resistant rocks such as shales and unconsolidated materials such as boulder clay. They are often unstable and tend to form less steep slopes that are more easily colonised by vegetation. Soft cliffs are subject to frequent slumping and landslips and this can occur especially where water percolates into the rock and affects its strength.
Cliff and cliff-top vegetation varies markedly even over short distances, changing in relation to slope angle, soil type and depth, freshwater run-off, nutrient enrichment caused by cliff-nesting birds, chemistry of the underlying rock, exposure to wind and salt spray, the water content and stability of the substrate and, on soft cliffs, the time elapsed since the last movement event. There is much local variability, with changing exposure around headlands.
The major natural and semi-natural cliff and cliff-top habitats in the UK are bare ground, spray-zone lichen covered rock, rock crevice, cliff ledge, seabird colony, perched saltmarsh, flushes, maritime grassland and maritime heath. Soft cliffs on sheltered coasts can develop under-cliff vegetation of woodland, scrub, tall herb and rank grassland, often very close to the sea.
The situation in the South East
|Extent in England||1,164 ha|
|Extent in the SE region||278 ha|
|Percentage UK resource in the SE||24%|
|Extent covered by SSSI designation||data to de added|
Rate of Change
|County||1998 extent (ha)||2008 extent (ha)|
|Isle of Wight||50|| app. 50
1998 data taken from 'The Biodiversity of South East England - An Audit and Assessment' published by the Wildlife Trusts of South East England and the RSPB, South East and Central Regions
2008 data taken from regional or national BAP habitat inventory.Please note that some of the changes listed here are due to improvements in mapping and habitat definition.
Erosion. Erosion 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. Cliff erosion in many places provides an essential supply of sediment to coasts lying down-drift of the cliffs.
Coastal protection. Coastal protection 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. Cliff faces may also be re-profiled and sown with hardy grasses of little value for nature conservation. All 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. A MAFF survey in 1994 identified over 90km of new cliff protection works likely to be needed in the next 10 years, resulting in a potential loss of 36% of the remaining soft cliff resource. Additional effects of such defences include both accelerated erosion and sediment starvation at coastal sites down-drift of defended sites. It has been estimated that sediment inputs may have declined by as much as 50% over the past 100 years due to cliff protection works.
Built development. There have been many instances in the UK of urban or industrial development and holiday accommodation being built too close to cliff-tops. Where the cliffs are subsequently discovered to be eroding, there is often political pressure to build the type of defensive works described above. Built development also prevents cliff-top biological communities from retreating in response to cliff erosion, subjecting them to a form of 'coastal squeeze'.
Agriculture. In traditional low-intensity grazing systems, livestock were grazed on cliff grasslands where they maintained open maritime grassland vegetation. 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. Localised eutrophication can be caused by fertiliser run-off from arable land above and this encourages coarse, vigorous 'weed' species at the expense of the maritime species. Agricultural land drains discharging on the cliff face may cause local acceleration of erosion.
Recreational use. The siting of holiday accommodation on cliff-tops not only reduces the landscape value of a site, but can also cause heavy localised erosion and disturbance to nesting birds. An increase in the number of walkers and dogs along some coastal footpaths has increased livestock worrying and even losses and forced a number of farmers to remove their stock from these sites. Consequently, some of the sites are now suffering from a lack of appropriate grazing, and scrub encroachment is likely to become a problem.
Introduced species. Predators, such as cats and rats, can have a significant impact on populations of cliff or burrow nesting seabirds, particularly on island sites. Also the spread of certain alien, invasive plants, especially members of the flowering plant family Aizoaceae such as the hottentot fig Carpobrotus edulis, can have a devastating impact indigenous maritime plant communities.
Vision for martime cliffs and slopes
The South East Biodiversity Forum’s vision for this habitat is that there should be:
No further loss of existing habitat • Good management, including visitor management, on all extant sites
No damage to site integrity from activities arising outside the sites, eg. inadequately managed public access
Re-creation of maritime cliffs and slopes on appropriate sites to restore some past losses, including the linking up of fragmented sites
Greater public appreciation of vegetated maritime cliffs and slopes and their specialist wildlife, including greater awareness of the impacts of human pressures, such as dog-walking, mountain-biking, dumping of waste.
Creation of alternative green space around important maritime cliffs and slopes under pressure for increasing new housing