Lesson ObjectivesLesson Objectives

To understand how changes in coastal ecosystems result from natural change and the direct and indirect impact of human activities.

What are we looking at?What are we looking at?

1. The distribution of sand dunes in the UK.

2. The key features of sand dune ecosystems.

3. The human impact on them and how they can be managed.

Sand dune systems are built over 100s of years. They start at the seaward side and gradually migrate landward, increasing in size as they go. They are in dynamic equilibrium – i.e. they are always changing to maintain the balance.

Similar to the different trophic levels in a food chain, the different stages in the system are called seres. Each sere is characterised by different vegetation. This sequence of vegetation change in a given area, where plant communities replace one another is known as succession (natural change).

Since the basis of this system is sand, the system is known as a psammosere.

What is the sand dune ecosystem?

Distribution of important sand Distribution of important sand dunes in the UKdunes in the UK

As you can see, the important sand dune complexes are concentrated in the Western Isles and eastern coast of Scotland, Wales, the north east coast of England and the northern part of the south west coast of England.

Although there are some exceptions, it is unusual to find sand dune systems on the South Coast.

4 conditions are needed to form large sand dune complexes: -

1. A sediment supply

2. A force (or onshore wind)

3. A wide, sandy beach which is exposed at low tide

4. Adequate vegetation to stabilise the dunes.

Formation of sand dunes

A steady supply of sand is required in order for sand dunes to form.

Generally, 20% of the sand is blown up the beach from the foreshore (the area between the high and low tide mark), hence it needs to be exposed at low tide. 80% is blown onto the dunes from the backshore (the area between the high tide line and the dunes)

Low tide mark

High tide mark

ForeshoreBackshore

Supply of sediment

The movement of our sediment supply (sand) on to the dunes is impossible without a force.

On the east coast of the UK, the strong winds come off the North Sea whereas on the west coast they come off the Atlantic.

A wind force

Suggestion: To ease your revision draw out this diagram and annotate it fully to avoid pages of notes.

A psammosere

Embryo dunes are the first in a sand dune ecosystem. As sand is blown up from the backshore, it collects behind shells and pieces of drift wood to form small heaps of sand.

These are colonised by grasses such as Sand Couch and Lyme grass, which can root in loose sand and tolerate moderate levels of salinity. The types of grasses have a waxy coating which enables them to retain water. The leaves are often rolled up, which reduces the leaf surface area exposed to the atmosphere, decreasing transpiration.

Since these are the first plants to grow, they are known as pioneer species. Lyme grass

Formation of embryo dunes

As the amount of sand that is deposited increases, the pioneer plants cannot grow quickly enough to avoid being smothered.

When the rate of deposition is greater than 30cm per year, Marram grass takes over the process of stabilising the dunes.

Marram grass can grow up to 1m per year and can spread sideways up to 3m per year, helping to trap the sand and keep it in one place.

Foredunes

Yellow dunes, so called because the patchy plant coverage exposes large areas of clean yellow sand, are predominantly characterised by Marram grass because of its deep root system and its ability to re-grow through newly deposited sand.

It, like the other grasses, have leaves which are able to fold to reduce its surface area, are waxy to reduce transpiration and which can be aligned to thewind direction.

Marram grass

Wind direction

Yellow dunes on the Sefton coast

Yellow dunes

Dune scrub stageAs a result of the humus from the previous stages, a sandy soil has now developed, which is able to support ‘pasture’ grasses and bushes. Species such as Hawthorn, Elder, Brambles and Sea Buckthorn (which has nitrogen fixing root nodules so can thrive in nutrient poor soil) are present.

As the scrub develops, shorter species will be shaded out.

HawthornBrambles

Elder Sea Buckthorn

Dune scrub

Grey dunesBy now, the dunes have more or less been covered in vegetation, anchoring the sand in one place.

As sand stops being deposited, the marram grass dies out and mosses and lichens colonise the dunes.

Humus from decaying vegetation combines with the lichens and mosses to give the dune a dirty, grey colour.

Where the sand consists of large quantities of sea shells, a calcareous soil will develop.

Where the sand is purely quartz grains, a more acidic soil will develop.

Older grey dunes which have been calcareous may become more acidic as the rain leaches nutrients from the soil.

Conifer PlantationsThe final seral stage in the sand dune system is the colonisation of conifers, such as Corsican Pine, which are very tolerant of salt and poor soils.

In some dune systems, these trees are planted, but the dunes will develop into woodland eventually regardless of this.

These final species in dune succession are known as the climatic climax vegetation. i.e. they are the ultimate vegetation, which are in harmony or equilibrium with their local environment.

Dune slacksThe hollows between the dune ‘ridges’ are known as ‘slacks’. They are often wet during much of the year since they are closer to the underlying water table. Consequently, they can support an unusual mix of plant and animal species.

Spiders and red leaf beetles are particularly common, as are Creeping Willow, marsh orchids and other herbaceous plants.

Dune slack

Red leaf beetle Marsh orchid

Creeping willow Rushes

Psammosere kite diagrams

Blow outs

A blow out at Oxwich Bay

Blow outs are erosional features within the sand dune system. Often caused by storms or human impact, they are formed where the wind is able to break through the vegetation and remove it. This exposes large semi-circular areas of sand that look rather like bunkers on a golf course!

Blow outs often take some time to be re-colonised by pioneer species.

Human impact on psammoseresThere are two forms of human impact on the sand dune ecosystem.

1. Direct impacts:

Human activities such as trail biking, rambling, picnics, school fieldtrips and even military training all disturb the equilibrium on the sand dunes. They destabilise the dunes, resulting in blow outs.

In addition, the dunes slacks may be breeding grounds for rare animals and these can be upset and endangered by human activity.

E.g. in Ainsdale, near Merseyside, the dune slacks are the breeding grounds of the rare natterjack toads. These are becoming endangered by trail biking.

e.g. in Oxwich Bay, South Wales, there are over 300,000 visitors per year, which includes 10,000 school students who trample over the dunes, destroying the vegetation.

Human impacts on psammoseres

2. Indirect impacts:

Increased management on the British coastlines is having an impact on the dune systems.

e.g. The building of sea defences reduces or completely removes the sediment supply required to feed the ecosystem.

e.g. Over management of the dunes results in the system being too stable. This results in the species diversity becoming less.

Coastal dune management

Coastal dunes are important ecosystems which contain 50% of the flowering plants in Britain.

They are the link between the sea and the land and because they are both important and fragile ecosystems, money needs to be spent to conserve and protect them.

Coastal dune managementSome of the strategies used to preserve and protect the sand dunes

are:

1. Aiding deposition of sand on the beaches by using groynes or beach replenishment.

2. Re-planting and watering dunes3. Fencing to restrict access, and banning trail bikes, horses and

dogs.4. Controlling visitor walkways.5. Education using signs, displays and visitor centres.6. Land use zoning – providing car parks, litter bins and toilets in

less sensitive areas. E.g. in Braunton Burrows, Devon.7. Creating nature reserves. E.g. in Oxwich Bay, South Wales8. Removing/controlling scrub either through burning (e.g.

Brauton Burrows) or through introducing controlled grazing by animals (e.g. Oxwich Bay).

References

http://www.seftoncoast.org.uk/shore_sanddunesprocess.html

http://www.coastalguide.org/dune/conserva.html

www.countrysideinfo.co.uk/successn/primary2.htm