Sefton Dunes

Coastal dunes cover 545 km² in the UK.

Sefton Dunes are located in northwest England and stretch for 17 km along the Irish Sea coast, between Mersey and Ribble estuaries, and are the largest area of coastal dunes in England.

This area has favourable conditions for dune development:

• a plentiful supply of sand delivered to the coastal zone by the Mersey and Ribble rivers
• a shallow offshore gradient
• prevailing onshore winds, blowing sand inland
• lowland coast

This dune environment has three principal features which run parallel to the coastline; mobile dunes, fixed dunes and dune slacks.

Primary succession in sand dune environments is called psammosere. As dunes get older inland from the high-water mark, the process of succession can be seen as a series of vegetation zones running parallel to the shore.

Mobile dunes are the youngest dunes and are located within 100m of the shoreline. They have sparse vegetation cover due to the harsh environmental conditions. These conditions include;

• exposure to strong winds and lack of shelter
• absence of dense vegetation to anchor the dunes, exposing plants to abrasive effects from blown sand
• shortage of fresh water (sand has high porosity)
• saline conditions
• lack of plant litter for soil development
• alkaline sands

Becasue of these condition, biodiversity is low and NPP (Net Primary Productivity) is limited. In addition, food webs are short.

Fixed dunes are older dunes that are found 200m from the shoreline and have complete vegetation cover and are fixed permanently in position.

Environmental conditions are less harsh, thus more favourable to plant growth. Thses dunes are more sheltered and have thin, but well developed soils that provide the minera nutrients and moisture for plants.

NPP and biodiversity are much higher and the nutrient cycle is richer.

Slacks are the depressions between dune ridges.

In slacks, the water table is at or near the surface, so, rather than drought being a problem. excess water is.

Specialised plants that are adapted to wet and aquatic conditions exist in slacks, these include creeping willow, rushes and flag iris. These plants that colonise the slacks create a freshwater hydrosere.

Dunes that form close to the high water mark are called embryo dunes and are only a few centimetres high. They have a sparse covering of sand couch grass (sand twitch) that trap enough sand to elevate the dunes above the mean high-water mark.

Sand couch grass is an example of a pioneer species as it is highly specialised, for example it is able to extract freshwater from salt water.

A few metres inland from the embryo dunes is the foredune ridge that rises to about 2m above the shoreline.

The foredunes are less exposed than embryo dunes and salt water incursion is less of a problem.

At Ainsdale, sand couch grass and marram grass dominate the foredunes, but, bare sand still comprises 40%.

These dunes at Ainsdale rise about 20m above the beach. This size shows the effectiveness of vegetation in trapping wind-blown sand.

Marram grass is still the dominant species and sand couch grass has disappeared. Other species include sea holly, thistles and lady's bedstraw. Marram grass is a xerophyte that is well adapted to the dry, exposed dune environment and is able to out-compete all other species.

The sand dune environment is also impacted by the marram grass as its dense growth adds organic matter and mineral nutrients to the sand, forming a skeletal soil which is able to retain some moisture. In addition, marram grass is able to stabilise the sand and provide shelter for other species further downwind.

Plant succession greatly modifies the environment of fixed dunes, with complete cover of vegetation, so there is less blown sand and winds are much lighter due to protection by the 1st dune ridge.

There is a shallow soil on the fixed dunes because the organic material from the plants mixes with sand and is neutral or slightly acidic. The soil acts as a store of mineral nutrients and moisture.

Specialised xerophytes, such as sea spurge, are still found, as well as a wide range of species, including bloody cranesbill, bird's foot and hawkweed. Further inland, woody plants and shrubs, like heather and hawthorn, start to grow.

The final vegetation community on the oldest dunes, under natural conditions, are a climax mixed oak-birch woodland. However, in Sefton, this is replaced by Scots pine that were planted as shelter belts between the late 19th Century and the 1930s.

For the past 100 years, human activity has been the main factor that drove the change in Sefton dunes' ecosystem. These changes have damaged the fragile dune environment, as well as the plants and animals that live there.

Originally, Sefton dunes covered 30km². However, as a result of residential development, golf courses, roads and holiday parks, only 20km² remain. 10km² of the remaining 20km² are in the same/similar natural state.