Plants at the Outer Harbour, August 2012
Tue 28 Aug 2012
A total of 52 different plant species were recorded but it is likely the total number is greater than this - some plants will have grown, flowered and died back earlier in the year and we may have missed others.
Some plants were present as single specimens e.g. Triticum aestivum (Bread Wheat) while others were present in large numbers e.g. Salsola kali (Prickly Saltwort), Atriplex prostrata (Spear leaved Orache) and Senecio vulgaris (Groundsel).
The Outer Harbour was created in winter 2009/10 and involved digging out shingle, sand and mud which was embanked to the east and south sides. These southern and eastern sides of the bank are steadily eroded by the tidal stream as it enters and leaves the main channel and a little more dredged material was added to the outsides on the east in winter 2010/11.
This is is a completely new habitat so how did so many plants colonise a newly created habitat so quickly – how did they get there? Some have seeds that are dispersed by wind e.g. Groundsels and Thistles. Many on the list, especially the typical salt marsh and sand dune plants have seeds that are dispersed by water, e.g. the Oraches and their seeds will have been present in the sand and gravel used to build the bank or washed up on it as it was being built. However, some are a bit of a puzzle and were probably carried there by birds or people. How did the solitary wheat seed get there? We think it possible that the seed of this and perhaps a few others such as Shepherd’s-purse were probably carried there either on the vehicles, such as dumper trucks that were used to build the bank or perhaps on the shoes or clothing of the people who operated them or on those of other people who may have walked on the bank before it was fenced off to protect the birds.
Some of the plants found on the bank are nationally scarce or restricted to small areas of the country, and some depend on a continual cycle of episodic shingle disturbance, such as Yellow Horned Poppy, and the Shrubby Sea Blight (Suaeda vera) which is common here but rare outside Lincolnshire, Norfolk and Essex and mainly found south of the UK to the Mediterranean. The Yellow Horned Poppy was found on Wells beach in 1998-2002* where sea defences had been constructed but is otherwise rarely seen on this part of the coast and has declined in Norfolk.
What does the future hold for this interesting plant community? The presence of the nesting birds and those that now roost there will be helping the plants by adding nutrients from their droppings to the otherwise rather nutrient-deficient sand and shingle. The plants also act as traps for wind blown organic matter which settles and rots and the plants themselves also contribute as they die and decompose. Many of the plants that have grown on the bank this year will have set seed and this will germinate next year so we intend to survey the area again at the same time next year. It will be interesting to compare what we find next year with this year’s list. However, the bank could be significantly modified by storms as has happened from time to time at other places along this coast in which case it will no doubt be rebuilt and the process of colonisation will start again.
Over the past two years, through natural processes, the surface of the bank has consolidated from loose shingle into a harder more stable mix of shingle and fine wind blown sand. Bushy plants such as Saltwort are actively trapping sand and initiating mounds and small dunes. This sand and fine shingle and shell particles is favoured by the terns for nesting, and was formerly a much commoner feature on this coast but is now very restricted due to frequent trampling of most beach areas by walkers and holiday visitors.
Where it remains undisturbed the bank top is likely to become more densely covered by grasses including Marram, and probably by Suaeda bushes (Seablite). Where this happens the bank will become less attractive to terns, although birds such as Ringed Plovers and Oystercatchers will still use it for nesting. However the need to maintain the bank as a shelter for the Outer Harbour means that some surface disturbance and shingle replacement will be necessary and this is likely to provide fresh shingle on which plant colonisation will re-start.
The plant list
Acer pseudoplatanus (Sycamore, very small seedling)
The plant names are those given in Stace, C.A. ‘New Flora of the British Isles, Third Edition, published in 2010 by Cambridge University Press.
Where the letters ‘sp’ occur in the list, as in Cirsium sp., Vicia sp. and Salicornia sp., we were unable with confidence to identify to species level so we have given the genus name. It is worth pointing out that Salicornia (Glassworts) are particularly difficult to identify to species level without fresh flowering material and use of a microscope.
All 51 of the plants seen were angiosperms (flowering plants). No lichens, mosses, ferns or gymnosperms were seen – unsurprising because angiosperms are generally much better at colonizing bare ground which is one of the secrets of their dominance of the World’s flora. Lichens and mosses are likely to colonise stable areas of the bank in future. Red poppy was also present on the bank earlier in the season taking the total to 52, although it is not known which of the four red poppy species it was.
* Erica Goode, Dorothy Vick, Madge Smith, ‘Wildflowers of Wells Next the Sea: 1998 - 2002’ 2002
Article by Chris Rose and Richard Price