Environmental Science
FACT SHEET www.curriculum-press.co.uk
Number 065
Investigating Sand Dunes Sand dunes are important habitats. In the exam, questions on sand dunes may test your understanding of succession, zonation, conservation management strategies or ecological sampling. You may decide to investigate sand dunes for your coursework. If so, remember that Environmental Science investigations must always have human impact as a central theme. So, if you are planning to do your investigation on sand dunes, you should be focussing on impacts of tourism or management techniques, for example.
This Factsheet summarises: • • •
These dunes increase in height as the plants grow, thus further decreasing wind speed. Marram grass is a very tough grass and can withstand desiccation, high salt levels and even burial. It is therefore, an extremely important plant in the formation of dunes.
the key features of sand dunes the practical approaches you might use, or be tested on, in exam questions recent exam questions and the most common mistakes students make in doing their own investigations and in exam questions
Marram grass has xerophytic features ie features that allow it to withstand desiccation (Fig 1).
How dunes form When the tide is low, sand bars become exposed. The wind can blow sand off these bars on to the beach. Dunes will form behind any object that slows down the sand-bearing wind. The leaves of plants such as marram grass (Ammophila arenaria) are very effective at slowing the wind so that small mounds of sand build up around the base of the plant.
Succession As a community develops, it alters its physical environment eg. root growth changes the physical and chemical nature of the soil by aerating it and adding exudates etc. The changed environmental conditions which result actually favour the colonisation and growth of different species which eventually give rise to a new community. This process of change is called succession.
Fig 1. Marram grass hairs reduce air movement/traps water vapour/traps air/increases relative humidity so there is less of a diffusion gradient for water vapour
Within the dunes, the initial organisms provide organic material for soil development. As this slowly continues, it enables the establishment of more advanced plant species, which in turn provide more organic material and encourages further soil development. As nvironmental conditions become more favourable, particularly due to soil accumulation, the level of primary production and so biomass increases. Species diversity also increases rapidly, with each successional stage having a dominant species, which is either the largest or the most abundant plant.
Section of a leaf of marram grass.
leaf rolled –this reduces external (exposed) surface area/increases relative humidity
The decline in species diversity approaching climax occurs because the dominant species out-competes other species.For example, oak trees in deciduous woodlands out-compete other species for sunlight, water and nutrients.
thick cuticle reduces evaporation/ diffusion of water/water loss
Sand dune succession Various zones can be recognised in a set of sand dunes which may represent different stages of succession (Fig 2)
Fig 2. 1 Embryo dunes – small scattered patches of marram grass which are largely selfseeded or growing from rhizomes which are up to 3m long. Only a very few species -Pioneer species can cope with the adverse conditions -salty, dry, nutrient-poor, shifting sand, intensely hot in Summer, cold in Winter
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2 Mobile dunes (yellow dunes) – some large areas of bare, moving sand but greater cover of marram grass.
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4 Fixed dunes – almost complete vegetation cover. Marram grass is sparse and is only found in isolated clumps before utlimately disappearing. Many other species of plants are present
5 Dune slacks – areas which develop where the sand becomes eroded so that the water table is reached. The sand forms a damp depression at low level and the area is prone to flooding in winter. Large numbers of rabbits keep the vegetation short but cause damage in ‘blow-outs’ where bare sand is exposed.
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6 Climax – sand dunes normally develop into scrub then woodland
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3 Semi-fixed dunes (or grey dunes) – smaller patches of bare sand with a greyish tinge. Many plants besides marram grass. increasing age of dunes
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