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Introduction The following summarises a study of the flora of dry stone walls in an area of the parish of Winsley, which is in West Wiltshire, about 6 miles from Bath and at the southern end of the Cotswolds. Apart from a few very limited descriptions, the only previous studies of dry stone wall flora I have located are those of Payne (1989), who gives a list of vascular plants found on mainly limestone dry stone walls in the Chew Valley in the Mendips, and Williams (1988), who does the same for walls built of acid rock in Shetland, with some reference also to bryophytes and lichens as groups. To my knowledge, the study reported here is the first systematic exploration of the flora of such walls in the Cotswolds, and the first to look in any detail at the lichens, mosses and liverworts which belong to this kind of community anywhere. A full account is provided in an article to appear shortly (Presland 2008). The external faces of dry stone walls the walls provide a surface on which plants and lichens can grow. This is our concern here. In what follows, the terms “flora” and “plants” are used, for simplicity, to include lichens and fungi, which are now regarded as being in different kingdoms from either animals or plants. The type of stone is a major determinant of the type of plant community found on walls. Limestone walls, such as those in the Winsley area, usually have a relatively rich flora, from lichens, through mosses and ferns to the higher plants. Lichens, early signs of life on these walls, favour exposed surfaces in pollution-free countryside. Mosses and liverworts clothe damper surfaces or places where a rudimentary soil is developing and create a more fertile soil for stonecrops, cranesbills, ivy and ferns to gain a foothold. Flora escapees from gardens further increase the variety Study methods For recording purposes, the study area was divided into stretches of road with convenient landmarks, each referred to as a site. Not all sites contained dry stone walls, and where they were present, they were often covered by Ivy, Clematis, hedge shrubs obscuring or markedly shading the walltop, or concreted at the top. Only walls which had at least the tops bare and unshaded bore plants of interest. Records were made of the plants growing on the top or of the walls or on the sides well clear of the ground. This provided a list of the plants in the flora of this environment and the number of sites in which each occurred. Below, I give an account of the flora in terms of these findings. Popular names of bryophytes are used, though they are frowned on by some bryologists. They are not vernacular names, but have been assigned by interested botanists, presumably in an attempt to make study of this group more accessible. Crustose lichens were not included in the systematic recording, partly because of identification difficulties. However, they occurred wherever the wall was bare and are the pioneers in this kind of environment. It is hoped to include images of the species mentioned on this site in due course. Results Crustose lichens from the study area which had been identified previously by lichenologists from specimens include Caloplaca aurantia, Caloplaca citrina, Lecanora campestris, and Lecanora calcarea, all typical of oolitic dry stone walls, and there are one or more unidentified black species. They were not recorded individually but were widespread. Overall, there were 27 dry stone wall sites at which specific recording of species occurred. At two of these, nothing significant was observed. So there were records from 25 sites. A total of 40 species of plants and fungi was recorded, though this was not the total occurring. The number of species recorded per site ranged from 0 to 16. Nineteen sites had ten or more species recorded, while a further four had five to nine species. This unpromising looking habitat therefore hosted a significant number of species, though not all were typically wall plants. The most common individual species recorded, in order of the number of sites in which they were seen on dry stone walls and the percentages of the 25 sites in which they occurred on such walls are listed below. Homalothecium sericeum (Silky Wall Feather-moss) - 24 sites (96%) All the above were seen mainly on wall tops, except Porella platyphylla, which was mainly on the sides. Other plants seen mainly on the wall tops were: Rhynchostegium confertum (Clustered Feather-moss) - 5 sites (20%) Other plants found mainly on the sides of walls rather than the tops (a more protected location) were: Polypodium interjectum (Intermediate Polypody) - 5 sites, 3 on the sides
and 2 on the tops of walls (20%) Also found were: Cladonia pyxidata (Cup-moss, actually a lichen) - 5 sites, occurring
where crumbling or distortion of walls created more or less horizontal surfaces
lower than the wall tops and therefore providing more shelter (20%) A number of other species occurred either once or twice, but are not of much interest because they are not typical wall plants. Overall, the results show that many of the plants which one might expect to find in this kind of environment were present at an encouraging number of sites. Development of the flora Unstructured observation locally and study of literature on limestone rocks and walls generally (Darlington 1981, Segal 1969), South Court Environmental Limited 1994) enable an account of the succession of vegetation on Winsley’s dry stone walls. The first species to occur, the pioneers, are crustose lichens, which have flat bodies which cling closely to the surface to minimise exposure to wind and cold. They can be found on both the tops and sides of walls. They are accompanied by particular species of moss, which are mainly on the horizontal surfaces - Tortula muralis (Wall Screw-moss), Grimmia pulvinata (Grey Cushion-moss) and Schistidium apocarpum (Common Beard-moss). These pioneers break off little fragments of rock as they grow and, with dead bits of their bodies and windblown particles of dust, a simple soil is formed on which more demanding plants can grow - more mosses and lichens, a few fungi and a variety of flowering plants and ferns. One of these is the greenish orange lichen Xanthoria parietina. Further mosses come in at this stage - mainly Bryum capillare (Greater Matted Thread-moss) and Orthotrichum anomalum (Anomalous Bristle-moss). As the soil becomes more substantial, further mosses appear on the wall tops, including Homalothecium sericeum (Silky Wall Feather-moss), Rhynchostegium confertum (Clustered Feather-moss) and Encalypta vulgaris (Common Extinguisher-moss). The liverwort Porella platyphylla (Wall Scale-moss) and the lichen Cladonia pyxidata (Cup-moss) also arrive, but mostly on the sides. The fungus Galerina pumila can occasionally be seen growing on wall-top mosses. Various flowering plants also invade, colonising mainly the wall tops, particularly: Geranium lucidum (Shining Cranesbill), Sedum acre (Biting Stonecrop), Saxifraga tridactylites (Rue-leaved Saxifrage), Geranium pyrenaicum (Hedgerow Cranesbill), Erophila verna (Common Whitlow-grass), Sedum rupestre (Reflexed Stonecrop), a garden escape which naturalises readily, and Centranthus ruber (Red Valerian) in one spot. Umbilicus rupestris (Wall Pennywort) occurs on the sides. A range of ferns occurs at this stage. The only one on wall tops is Polypodium interjectum (Intermediate Polypody). It also is found on the sides, as are Asplenium ruta-muraria (Wall-rue), Ceterach officinarum (Rusty-back) and Phyllitis scolopendrium (Hart’s-tongue). Where next? A number of key questions can be identified relating to the flora of dry stone walls and these are listed below. Investigations for them are already in progress, and it is hoped to include results on this site soon. 1. What kinds of plants, lichens and fungi grow on dry stone walls elsewhere? 2. Which of these organisms grow on limestone dry stone walls and which on walls constructed of acid rocks? 3. Is the flora of dry stone walls significantly and consistently different from that of mortared walls? 4. Can the flora of dry stone walls be distinguished from the flora of the surrounding environment? 5. How does the flora of dry stone walls fit into the National Vegetation Classification? 6. How can the flora of dry stone walls be conserved and enhanced? These questions are all under investigation in Winsley or elsewhere and findings are expected to appear in various publications and on this site in due course. Further information from John Presland, 175c Ashley Lane, Winsley, Bradford-on-Avon, Wilts BA15 2HR. Tel 01225 865125 References Darlington A (1981) Ecology of Walls. Heinemann Educational, London. Payne R M (1989) The flora of walls in the Chew Valley. Somerset Archaeology and Natural History 133: 231-242 Presland J (2008) Dry stone walls in Winsley: their flora and its conservation. Wiltshire Botany 10, awaiting publication. Segal S (1969) Ecological Notes on Wall Vegetation. Dr. W. Junk N. V., The Hague: South Court Environmental Limited (1994) What’s on a Wall? The Ecology of Walls, edn 3. South Court Environmental Limited, Northampton. Williams L. (1988) Observations on the flora of wall habitats on Yell, Shetland, in J. A. Fowler ed. Ecological Studies in the Maritime Approaches to the Shetland oil Terminal: Report of the Leicester Polytechnic to Shetland, August 1986 and July 1987. Leicester Polytechnic, Leicester. John Presland, September 2007 |