Sea Sandwort colonisation & sand erosion at Rhossili

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Sea Sandwort, Honckenya peploides, is a small, low-growing, fairly fleshy plant that lives on the upper beach where it forms a rapidly spreading carpet of vegetation by means of an extensive stolon system beneath the surface of the sediments.  Sea Sandwort frequently grows where strand-line debris has trapped drifting sand. When Sea Sandwort plants colonise this habitat, they impede and hold even more drifting sand particles amongst their leaves, stems, and root systems. These plants can therefore be important pioneers that help to stabilise the foreshore and act as a precursor to the formation of dune systems.

You could see this happening on Rhossili beach in  July this year. The first three photographs in this posting show a colony of Sea Sandwort growing well on an accumulation of sand near the top of the shore close to the solifluction terrace escarpment at the base of Rhossili Down. This species was one of several pioneering plant communities acting as sand stabilisers along the length of the beach.

However, by late October this year, these plant colonies had either been severely damaged or eradicated totally. Using the Sea Sandwort as an example, it is possible to compare the July pictures with the October ones of the same plant stand, and to see how the mound of sand on which the plants were living has been largely removed. It is likely that the extreme high tides around 16th October 2012 (predicted height of 10.14 metres above Chart Datum at Mumbles), driven by strong onshore winds, washed the sand away. The seaward edge of the mound has been truncated to form a low cliff-like face. Many of the plant stems and roots are now exposed to the air, hanging like a curtain over the vertical edge of the remaining block of sand, or draped like streamers over the flat surface of the shore.

Similar changes to the beach environment, probably caused by the same natural event, could be witnessed elsewhere along Rhossili beach. Extensive tracts of both sand dunes and terrace escarpment have been cut back by the waves leaving vertical faces up to 2 metres high where once there were gradual slopes of sediments partially vegetated by maritime plants such as marram grass, sea holly, sea bindweed and more.


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2 Replies to “Sea Sandwort colonisation & sand erosion at Rhossili”

  1. Yes, solifluction is a great word. I had forgotten till your comment that I had explained the geological phenomenon that it describes in earlier posts that were waiting for update. I’ve done that now. So, if anyone wants to know more about solifluction, they can enter it as a search word in my blog and get a list of all the posts that mention it.


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