Clevedon Pill, North Somerset – Saltmarsh Survey 2013
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Clevedon Pill, North Somerset – Saltmarsh Survey 2013 Introduction Clevedon ‘Pill’ is a small inlet south of Wain’s Hill where the Land Yeo and the Blind Yeo flow out into the Severn Estuary. The Blind Yeo is a man-made drainage ditch that receives its water from the many local rhynes, which also provide boundaries for the local fields. The flow is controlled by sluice gates. The Land Yeo is a small river that starts near Dundry on the Mendip Hills and flows via Nailsea to Clevedon. It flows through the centre of Clevedon, although it is often lost to view behind the houses. In 2004 the sea defences here were improved by raising the bank to the seaward side of Marshall’s Field and installing new sluices to control the flows from both the Land Yeo and the Blind Yeo. The blue line shows the Mean High Water Mark: the average of all the High Water levels recorded over a long period The whole area of the Clevedon coastline is a Site of Special Scientific Interest (SSSI), primarily because it has some particularly interesting geology, but the flora is interesting too. Area surveyed The area surveyed in 2013 was from the corner of the Boat Store at ST391705 boat store to the Sluice Gate of the Blind Yeo at ST392702, using the upper (seaward) footpath as the landward boundary (see arrows on map below) The Pill is tidal, the water varying in its salt content from the mudflats, which are flooded twice daily, through the saltmarsh up to the sea defences. The tidal range is very large – up to 14 metres in the Severn Estuary – so the area between low and high water is extensive; a fact not lost on the many waders and wetland species that feed here. Left Clevedon Pill with the Land Yeo in the foreground at low tide. Right Clevedon Pill at High Tide (yes they are the same boats!) taken 1 hr after HW – tide height was 12m There is a large Reed Bed (see below) at the land-ward end of the saltmarsh, which is only flooded at High Water Spring Tides, and beyond that is grassy scrubland with a few stunted trees and an artificially created bank which is colonized by flowers somewhat more typical of the limestone grassland. Survey Methods The area was surveyed approximately every two weeks from January to October 2013. Plants were identified using New Flora of the British Isles by Clive Stace (second edition), The Wild Flower Key by Francis Rose, Grasses by C E Hubbard and The Collins Guide by D McClintock and RSR Fitter. Plant species were recorded on an Excel Spreadsheet. Abundance was estimated using the DAFOR scale. The plants were photographed and monthly updates were added to a blog at http://clevedonpillflora.wordpress.com The extent of the Reed Bed (black line) and the seaward extent of the saltmarsh (yellow line) were recorded using GPS. Observations on the Saltmarsh Flora A total of 95 flowering plant species were recorded and 10 species of Algae. Most saltmarshes show a typical zonation, with the most salt-tolerant plants found at the seaward edge, and the least tolerant where they are only flooded with seawater at High Water during Spring Tides. This zonation also varies with the amount of disturbance the area receives from wind and wave action and also the stability, or otherwise, of the mud. The number of species found in the seaward parts of the saltmarsh is small compared to those found above the Mean High Water mark (see below). Number of species found in lower, middle and upper shore Lower Lower/ middle Middle Upper The zonation is not clear cut; some species such as Plantago maritima are found all over the site, also Aster tripolium and Limonium vulgare. The description that follows is not comprehensive but will give some idea of the character of the site. The seaward extent of the saltmarsh, at low tide, looking towards Blackstone Rocks (left) and towards Wain’s Hill (right) Lower Shore The mud flats are first colonised by an assortment of green alga forming extensive bright green cushions (see below left) – these include Derbesia sp and Ulva prolifera mixed with Rhizoclonium riparium. There are also isolated clumps of Spartina anglica both on the mud and also on the rocky shore (see below, right). The stabilised mud(see below) is colonised by several species, including Puccinellia maritima, extensive communities of Plantago maritima and abundant Aster tripolium, also Triglochin maritima, Limonium vulgare, Armeria maritima, Spergularia media and Sueda maritima. Puccinellia maritima (under water), Plantago maritima, Aster tripolium and Sueda maritima (pale green, centre). An assortment of green algae, mainly Ulva prolifera and Ulva intestinalis also Ulva lactuca and possibly other microscopic species, can also be seen in the channels and ponds that criss-cross the seaward part of the saltmarsh. Lining the banks of the Land Yeo and the channels to the landward side of the saltmarsh are extensive communities of Triglochin maritima, and Aster tripolium - also Cochlearia anglica which was very obvious early in the year and seems to be an important coloniser of the freshwater channels. Triglochin maritima, Aster tripolium and Cochlearia anglica on the banks of the Land Yeo Middle Shore Further up the shore there are extensive stands of sedges and rushes especially Carex extensa and Juncus gerardii and grasses including Sea Couch, Elytrigia atherica and Festuca rubra. Aster tripolium and Limonium vulgare can also be found here along with Glaux maritima. Upper Shore The upper shore is dominated by a large reed bed (Phragmites australis). Behind the reed bed are patches of a variety of interesting sedges and rushes including the impressive plants of the Greater Pond Sedge, Carex riparia. Hemlock Water Dropwort, Oenanthe crocata and Wild Angelica Angelica sylvestris grow here, together with Wild Carrot, Daucus carota and Common Fleabane, Pulicaria dysenterica. This area merges into the sea defences, a steep bank dominated by grasses, docks and Black Knapweed Centaurea nigra, with quite a variety of small leguminous plants, as well as a large stand of Tall Melilot, Melilotus altissimus in the more sheltered part of the bay. A small stand of Tree Mallows (Malva arborea) can also be seen. Acknowledgements and thanks Thanks are due to several local botanists. Our local Tree Warden, Angela Slotte helped me to get started, Dr Helena Crouch, Vice Recorder for VC6 and Pam Millman of the Somerset Rare Plants Group gave advice on identification, and Katherine Slade from Cardiff Natural History, National Museum of Wales identified the Chlorophyta. Other references Adam P (1981), The Vegetation of British Saltmarshes. New Phytologist Volume 88, Issue 1,143–196. 1981 Thompson D, McNeilly T and Gray AJ Population variation in Spartina anglica (CE Hubbard) New Phytologist Volume 117, Issue 1 129–139 1991 Dee Holladay 20/10/13 Plants found at Clevedon Pill (Saltmarsh to upper footpath) 2013 DAFOR L/M/U shore Achillea millefolium Yarrow O U Agrostis stolonifera Creeping Bent F U Alopecurus pratensis Meadow Foxtail F U Angelica sylvestris Wild Angelica O U Anthriscus sylvestris Cow Parsley O U Apium graveolens Wild Celery O U Armeria maritima Thrift A LM Armoracia rusticana Horse-radish O U Arrhenatherum elatius False Oat-grass F U Aster tripolium Sea Aster A LM Atriplex glabriuscula Babington's Orache F MU Atriplex prostrata Spear-leaved Orache F U Barbarea sp Winter Cress O U Beta vulgaris Sea Beet F U Brassica rapa Wild Turnip O U Carex extensa Long-bracted Sedge O MU Carex flacca Glaucous Sedge O U Carex hirta Hairy Sedge O U Carex otrubae Fox Sedge O U Carex riparia Greater Pond Sedge R U Centaurea nigra Black Knapweed F U Cirsium arvense Creeping thistle O U Cochlearia anglica Scurvy grass A LM Convolvulus arvensis Field Bindweed O U Crepis vesicaria Beaked hawk's Beard O U Crithmum maritimum Rock Samphire O U Crocosmia x crocosmiiflora Montbretia R U Cynosurus cristatus Crested Dog's-tail F U Dactylis glomerata Cock's-foot F U Daucus carota Wild Carrot F U Dipsacus fullonum Wild Teasel O U Elytrigia atherica Sea Couch A MU Fallopia japonica Japanese Knotweed R M Festuca rubra Red Fescue A LM Ficaria verna Lesser Celandine O U Filipendula ulmeria Meadowsweet O U Galium palustre Common Marsh bedstraw O U Galium verum Lady's Bedstraw O U Glaux maritima Sea milkwort A M Heracleum spondylium Hogweed F U Juncus gerardii Mud/Saltmarsh Rush A M Juncus inflexus Hard Rush O U Lathyrus nissolia Grass Vetchling O U Lathyrus pratensis Meadow Vetchling O U Lemna sp Duckweed O L Leucanthemum vulgare Oxeye Daisy O U Leucojum aestivum Summer Snowflake R U Limonium vulgare Sea lavender A LM Lotus corniculatus Birds-foot Trefoil F U Malus pumila Apple O U Malva arborea Tree Mallow O U Medicago lupulina Black Medick O U Melilotus altissimus Tall Melilot F U Oenanthe crocata Hemlock Water Dropwort F U Parapholis strigosa Sea Hardgrass ? U Persicaria amphibia Amphibious Bistort O U Phleum pratense Timothy Grass F U Phragmites australis Common Reed A U Picris echioides Prickly Ox tongue O U Plantago coronopus Buck's-horn Plantain O U Plantago lanceolata Ribwort Plantain F U Plantago major Hoary Plantain O U Plantago maritima Sea Plantain D LM Poa pratensis Smooth Meadow Grass F U Polygonium aviculare Knotgrass F U Potentilla reptans Creeping Cinquefoil O U Primula vulgaris Primrose R U Prunella vulgaris Self Heal O U Puccinellia maritima Common Saltmarsh Grass A L Pulicaria dysenterica Common Fleabane F U Raphanus raphanistrum ssp mari Sea Radish F U Rosa canina Dog Rose O U Rumex conglomeratus Sharp Dock O U Rumex crispus Curled Dock F U Rumex obtusifolius Broad-leaved