The humid dune slacks support a population of the Annex II species petalwort Petalophyllum ralfsii for which the site is also selected. Morrich More in north-east Scotland is one of the largest acidic dune sites in the UK.
The sequence of development has resulted in the formation of extensive humid slack communities of an acidic character which lie as parallel hollows between the dune ridges and form part of a complex mosaic of dune habitats, several of which have been proposed as Annex I habitat types in their own right.
This is the most important acidic dune system in Scotland, owing to its size and the exceptional diversity of the habitats within it. Studland Dunes is a large acidic dune system in south-west England with well-conserved structure and function.
The site has been intensively studied. The structure and function of dune systems are well-represented with dune-building processes still active. These processes have resulted in the formation of acidic humid dune slack communities with a high water table, which lie in the parallel hollows between the dune ridges.
In these slacks, acidic fen and reedbeds have developed. Some areas are dominated by grey willow Salix cinerea and birch Betula sp. The dune slacks are linked to an area of open fresh water known as the Little Sea. Kenfig in south Wales contains the most important example of Humid dune slacks in the UK, owing to the extent of the habitat type and the conservation of its structure and function.
These calcareous dune slacks are also amongst the most species-rich in the UK, supporting communities dominated by a variety of mosses and a number of rare plants, notably Fen orchid Liparis loeselii , for which the site is also selected. Some of the dune slacks on the site are still in the early successional stage of development. Magilligan in Northern Ireland is one of the largest dune systems in the UK. It has an extensive and well-developed series of Humid dune slacks , which contain virtually all of the dune slack vegetation in Northern Ireland.
The dunes are of an acidic character. A wide range of slack vegetation occurs on the site, including wet open dune slacks at an early successional stage, slacks dominated by creeping willow Salix repens ssp.
The hydrology of the site is little modified and the structure and function of the site are therefore well-conserved.
Dune slacks are particularly well-represented at Sandscale Haws, the largest calcareous dune system in Cumbria. The slacks support a good range of vegetation communities and are very species-rich.
Several uncommon species including marsh helleborine Epipactis palustris , dune helleborine Epipactis dunensis and coralroot orchid Corallorhiza trifida occur. Examples of three different humid dune slack communities have been recorded within the complex. The dune slack vegetation with silverweed Potentilla anserina and common sedge Carex nigra is particularly well-developed. They are formed in two ways.
Primary dune slacks are formed on rapidly accreting coasts where the top of the beach is cut off from the sea by a dune ridge forming further out on the beach. This is occurring on the Sefton Coast at Birkdale, a feature known locally as the green beach. Primary dune slacks are long and narrow and parallel to the coast. Secondary dune slacks result from a blowout, where erosion down to the water table has occurred. If the erosion is extensive, a large flat area of wet sand is exposed.
Most of the dune slacks on the Sefton Coast are secondary dune slacks and they are orientated at right angles to the coast, parallel to the prevailing wind direction. The dune water table fluctuates annually because of the differences in rainfall and evapo-transpiration between the summer and winter months. Because of this, many dune slacks are flooded during the winter period.
Dune slack at Ainsdale during the winter The wet sand created by secondary dune slack formation is colonised by plants and a succession occurs. This succession on wet sand, however, is very different to that on the dry dunes. Dune habitats can look different in different locations.
To watch a video about Embryo Dunes in Lincolnshire, click here. With plant roots now reaching deep into the dune, semi-fixed dunes are pretty stable, but you can still see exposed sand on their surface which is able to move. These dunes will continue to accrete sand from the beach and, the sand on these dunes can be blown over the ridge and inland to grow the dunes behind them.
These are also known as yellow dunes because of the colour of the sand. Sand dunes are separated by dips, called dune slacks. Slacks are formed in two ways — either when a new dune ridge forms in front of a low-lying area which cuts it off from the sea, or when a dune blowout forms in an area that's got lots of vegetation, exposing a dip of bare sand.
Where these low areas are low enough to meet the dune water table, freshwater pools can form. These slacks are fantastic habitats for dune wildlife such as natterjack toads, which use the pools for breeding. As you move further away from the beach, the dunes become less yellow in colour and begin to turn grey. This is because these dunes are starting to build up more humus the broken-down organic plant matter which is found in soil from the diverse plant life and bacteria which now lives in these stable dunes.
These dunes are also better at holding in water, making them able to support larger shrubs. These are also known as grey dunes and can still have sand blowing through them from blowouts, the semi-fixed dunes or even from the beach on a really windy day!
To watch a video about Fixed Dunes in Cumbria, click here. Dune heaths are found on the more acidic sandy areas where rain has leached out the lime from the sand.
Here you can find many species of heather, lichens and fine grasses, often with a thin layer of peaty soil. Behind some sand dune systems, salt marshes can form where sheltered estuaries or creeks can deposit fine sediments, or where where gentle tidal waters can deposit sediments. In the following, we will discuss the complex interactions between dune slack vegetation, hydrological conditions, and management in dune slacks in order to conserve or restore these ecosystems for future generations.
The examples discussed will be mostly from the NW European dune areas, where dune areas have been affected very negatively by human activities, such as mass recreation, abstraction of drinking water for large cities, increased atmospheric nitrogen deposition from industrial and agricultural areas, and large-scale afforestation Van Dijk and Grootjans This destruction of what is seen by many as the last remnants of natural ecosystems led to much societal opposition during the last decades and many restoration projects were initiated to restore dune ecosystems with a high biodiversity Kooijman, Chap.
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