Video of the site
View the video clip of the site and the survey. A film transcript is also provided below.
Video showing the site and the survey
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Film Transcript
Sand dunes are excellent places to study ecological succession - especially when they are actively forming - like this one on the Atlantic coast of Portugal. The dune in this exercise consists of a sandy spit running in an east-west direction along the coast. Inland, behind the spit lies an extensive estuary formed by two rivers.
We shall be investigating how the developing dunes become colonized by plants and how the plant community drives the successional development of the dune. To do this we shall be sampling along a line running northwards at right angles to the sea. As we move inland we survey increasingly older parts of the dunes.
At the top of the beach, just past the high water mark, sand is pushed and blown into loose heaps known as the yellow dune. Within a few metres plants begin colonizing the sand - species like marram- a tough grass able to endure salt spray and burial in the shifting sand. It stabilises loose sand so consolidating the dune. Other pioneer species such as sea holly and sea daffodil can also be found - both have specialised underground structures in the form of swollen roots or bulbs which enable them to conserve water and resources.
Our transect starts here and extends inland for 260m. We sample at 10m intervals, using a 0.25 metre square quadrat. Percentage cover of plants in each quadrat is visually assessed. Soil samples are also taken at each sampling point. These will be analysed for sodium levels and organic matter. This will enable us to examine possible changes in the abiotic and biotic conditions which direct the pattern of the succession.
Further inland and we notice a change in the landscape. There is less bare sand - we are now in what is referred to as the grey dune. Around 90m from the high water mark the sandhills are lower and the vegetation appears more established. There is a greater degree of plant cover here. There are more perennials such as the restharrow Ononis natrix and annuals such as the pink-flowered catchfly Silene colorata which are able to grow in the sheltered lea of the yellow dune.
By 200m there is a substantial increase in ground cover with a noticeable presence of grasses species. This is known as the back dune and supports the longest established dune community. We end our transect at 260m as shortly after this the succession ends because of the nearby estuary. Data from the transect can be used to follow the development of the plant community. Additionally, changes in the salt content and the amount of organic material will help explain how abiotic factors control the dune community and how the developing plant community is itself an agent of change.
