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Examine the role of vegetation in the initiation and morphological development of coastal dune systems.

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Introduction

Katy Scott Effective Learning Skills Geography Summative Writing Assignment Examine the role of vegetation in the initiation and morphological development of coastal dune systems 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. ...read more.

Middle

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) ...read more.

Conclusion

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. Appendix 1 Common name Scientific name Plants of the strandline Sea rocket Cakile maritima Prickly saltwort Salsola kali Frosted orache Atriplex laciniata Plants of embryo dunes Sand couch Elytrigia juncea Lyme-grass Leymus arenarius Plants of fore or yellow dunes Marram grass Ammophila arenaria Sea bindweed Calystegia soldanella Hound's-tongue Cynoglossum officinale Sea holly Eryngium maritimum Isle of Man cabbage Coincya monensis ssp. monensis Portland spurge Euphorbia portlandica Sea spurge Euphorbia paralias Seaside pansy Viola tricolor ssp. curtsii Dune fescue Vulpia fasciculata Plants of grey dunes Red fescue Festuca rubra Bloody crane's-bill Geranium sanguineum Common broomrape Orobanche minor Seaside centaury Centaurium littorale Green-flowered helleborine Epipactis phyllanthes Dune helleborine Epipactis leptochila var. dunensis. Plants of older (de-calcified) fixed dunes Common bent-grass Agrostis capillaris Heather Calluna vulgaris Yellow bartsia Parentucellia viscosa Slender parsley-piert Aphanes australis Fine-leaved sheep's-fescue Festuca filiformis (tenuifolia) Dune scrub plants Willow spp. Salix spp. Sea buckthorn Hippophae rhamnoides Pyramidal orchid Anacamptis pyramidalis Plants of dune slacks Creeping bent-grass Agrostis stolonifera Creeping willow Salix repens Knotted pearlwort Sagina nodosa Grass-of-Parnassus Parnassia palustris Small-fruited yellow-sedge Carex viridula subsp. viridula Chaffweed Anagallis minima Baltic rush hybrid Juncus balticus x J. ...read more.

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