We use cookies to give you the best experience possible. By continuing we’ll assume you’re on board with our cookie policy

Vegetation in the Initiation and Morphological Development of Coastal Dune Systems Essay Sample

essay
The whole doc is available only for registered users OPEN DOC
  • Pages:
  • Word count: 1115
  • Category: geography

Get Full Essay

Get access to this section to get all help you need with your essay and educational issues.

Get Access

Vegetation in the Initiation and Morphological Development of Coastal Dune Systems Essay Sample

Sand dunes are a distinctive coastal feature and specialized habitat. Dunes form where an obstacle such as a shingle ridge or vegetation traps a supply of dry, wind-blown sand. Active dune systems require an adequate supply of sand, which is normally sourced from beaches, which dry out between high tides. The sand blown inshore to form dunes is replaced by wave action, ensuring a constant supply of sandy material. Dunes are produced by wind transport of sand, supplied by marine processes, but the nature of the wind activity is critical in determining dune morphology and distribution. Sand may be derived from a variety of sources – offshore glacial material, erosion of coastal deposits (existing dunes, coastal cliffs, etc.), shell fragments from marine sources (as in the Outer Hebrides) and rivers. The interplay between sand availability, sand movement, vegetation and water table level is crucial in determining dune morphology and evolution. Many coastal environments are charaterised by accumulations of sand in the backshore zone. Figure 1 shows coastal sand dune distribution in United Kingdom.

There are two main types of coastal dune, vegetated and transverse. The most common type of coastal dune is vegetated and displays complex interaction between its vegetation and sand transport. The presence of vegetation causes these dunes to develop by the deposition of low angle beds of sand. These dunes have irregular surfaces and dune crests that are seperated by blowouts or slacks (Hansom 1990).

The formation of coastal dunes requires that the vegetation cover should be sparse or absent for at least a part of the year, as the plants bind the soil surface and the stems reduce the power of the winds (Chepil & Woodruff 1963). It is hard for plants to spread over loose, dry, barren sand surfaces, which may be fatally hot in the sunshine. On dune coasts the plants also have to cope with the drying and tearing action of the wind, abrasion, salt spray, saltwater flooding, heat, drought, burial in sand and a limited supply of nutrients. In addition, the wind blows the seeds away from the open sand surfaces and therefore hinders the spread of a vegetation cover. Such influences increase in intensity during storm events. Some plants are able to survive and even flourish. Species such as Spinifex are able to change their form (morphology) in response to changing conditions. (See appendix 1 for more dune species).

Even a sparse vegetation cover will weaken the power of wind, shelter the ground surface and trap sand grains (Wolfe & Nickling 1993). Dune plants are xenomorphic, i.e. they have adapted to tolerating dryness. They have long roots that reach down to the lower, humid sand layers, and their stems can survive bending by the wind.

As you can see from the diagram above (Figure 2), the sand dunes are divided into zones. Different vegetation species grow in each of the zones, in relation to how long the sand deposits have been there. The degree of stability is very important in determining which plants become established. Embryonic dunes are nearest to the sea and have few plants growing on them except lyme (Leymus arenarius) and marram grass (Ammophila arenaria) (Figure 3). This is a coarse, long-leaved grass found only on sand dunes, where it is abundant and an important part of the structure and ecology of the dune systems. It binds loose, wind-blown sand with a network of branching rhizomes. Its ability to do this means that it is perfectly equipped to cope with deposition rates of up to 1m of sand per year. The growth of marram is directly related to the rate of influx of sand.

As more sand accumulates, the embryo dunes join to form fore dunes which can reach a height of 5m. Fore dunes are also often known as yellow dunes, on account of the amount of bare sand yet to be colonised. Landwards of the fore dune, the increasing amount of vegetation means that sand movement is more restricted, however, as the dunes are higher, the velocity of the wind is much greater. The dune eventually reaches a point where these strong winds remove as much sand as they deposit. As the sand is still mobile, marram grass is the dominant species although grasses such as red fescue (Festuca rubra) (Figure 4) and sand sedge (Carex arenaria) (Figure 5) invade (Hansom 1990). Landwards of the yellow dune, the dunes become increasingly grey as humus and bacteria from plants and animals are added and the dune is occupied by grey-coloured lichens, mosses and low lying shrubs such as buckthorn (Figure 6). These grey dunes can reach heights of 10-30m before the supply of fresh sand is cut off because of their increasing distance from the beach (Waugh 1995).

Almost all dune systems are subject to erosion, whether it is a natural threat or one created by human activity. Some of the natural threats include falling water tables. In dune slacks, temporary and sometimes permanent ponds form. Here, the ecosystem is stressed due to the seasonal changes in the habitat, so therefore only specialised species are able to survive. Water tables tend to vary from year to year, but a particularly long period of low water tables would put too much stress on the ecosystem and many specialised species would be unable to cope, and be replaced with coarse vegetation and scrub. Another natural threat is grazing. Grazing is needed to maintain fixed dune communities and prevent the dunes developing into scrub and woodland.

However, if the dunes are over-grazed by livestock and rabbits, then this can have damaging effects, but if the dunes are under-grazed, the scrub and woodland species will begin to grow. Humans cause interference as sand dunes are very popular with tourists. Holiday makers may walk through them or park their cars on them. The dunes can cope with pedestrians to an extent, but cars and walkways from car parks to the beach cause a great deal of damage. Embryo dunes are formed when sand is blown up the beach and trapped by pioneer species of plant such as marram grass. When pedestrians continually walk in these areas these very important plant species may be destroyed and sand is no longer trapped. Failure of the dune vegetation to recover from any damage, may result in dune erosion due to the effects of onshore winds mobilising bare sand in the form of blowouts. Movement of sand landward results in erosion of the beach/dune system. The blowouts that induce this mode of erosion may in turn initiate further degradation within landward dunes as drifting sand buries and kills vegetation in its path.

We can write a custom essay

According to Your Specific Requirements

Order an essay

You May Also Find These Documents Helpful

Social Sciences: Geography, Anthropology, Sociology, Eeconomics and...

Geography is the study of the physical parts of the earth and its atmosphere, geography can also be the study of the human activity. Every day, geography affects our daily lives. Examples of geography affecting us on a regular basis are shown from everyday experiences. The environment constantly affects us, whether it be by weather and climate change or giving us natural resources like energy...

Geographical Investigation into sub session on the...

Aims: The key question for this enquiry is: "How and why does vegetation change along a psammosere succession?" This question states that, I must investigate into how the vegetation changes on the sand dunes through the heath land. With this key question, there are subheadings as shown below: * How does the number of plant species change through the succession? This question states, that I...

Geography Erosional Landforms

Corrie = Corries, also known as cirques, are often the starting point of a glacier. Snowflakes collect in a hollow. As more snow falls, the snow is compressed and the air is squeezed out to become firm. With the pressure of more layers of snow, the firm will, over thousands of years, become glacier ice. Erosion and weathering by abrasion, plucking and freeze-thaw action will...

Riverwalk vs River Front

Everything new eventually becomes less new, and then -- although no-one can say precisely when -- old.  Sometimes when there has been rapid advancement in one area of a city, the contrast between the old and new can be startling. Such is the case with the old river-walk and new riverfront areas of the Las Olas area in Fort Lauderdale. Starting from the year "1917,...

Villa Solheira

The villa’s character is highlighted by a charming outdoor garden, a swimming pool, and a terrace, all looking out to a striking view in this side of the Algarve. The climate is excellent in this sunny region—warm and even all year long, The villa has all the things needed to enjoy a private comfortable lifestyle. Families will absolutely love the villa’s luxurious interiors, with its...

Get Access To The Full Essay
icon
300+
Materials Daily
icon
100,000+ Subjects
2000+ Topics
icon
Free Plagiarism
Checker
icon
All Materials
are Cataloged Well

Sorry, but copying text is forbidden on this website. If you need this or any other sample, we can send it to you via email.

By clicking "SEND", you agree to our terms of service and privacy policy. We'll occasionally send you account related and promo emails.
Sorry, but only registered users have full access

How about getting this access
immediately?

Become a member

Your Answer Is Very Helpful For Us
Thank You A Lot!

logo

Emma Taylor

online

Hi there!
Would you like to get such a paper?
How about getting a customized one?

Couldn't Find What You Looking For?

Get access to our huge knowledge base which is continuously updated

Next Update Will Be About:
14 : 59 : 59
Become a Member