Wall Ferns

Walls provide a variety of habitats in which ferns can grow, including crevices and joints between the stones, on the wall tops where small amounts of soil build up and also on the stones themselves. Several native ferns of the Spleenwort (Asplenium) family are found growing on walls within Hull. Species recorded in Hull include Wall-rue (Asplenium ruta-muraria), Maidenhair Spleenwort (Asplenium trichomanes) and Black Spleenwort (Asplenium adiantum-nigrum).

 Wall-rue shows a distinct preference for limestone when growing on natural rock and it finds similar conditions in the mortar of walls, where it is more commonly found. It is the typical pioneer species of wall vegetation over most of Europe. Many young plants are often found where mortar has broken away to form small ledges and crevices. Maidenhair Spleenwort usually grows on mortared walls and in rock crevices, preferring surfaces that face south-west. This species is not confined to any particular kind of rock though it is often abundant on limestone. Black Spleenwort grows most commonly on hedge banks and is generally uncommon on mortared walls.

 Hart's-tongue (Phyllitis scolopendrium) and Rustyback (Ceterach officinarum) are also found within the City. The usual habitat of Hart's-tongue is hedge banks, but it is commonly found on old walls, on rocks or sometimes in woods. This fern shows a distinct preference for limestone and lime-rich soils. Rustyback is naturally a plant of crevices in limestone but such conditions are simulated in mortared walls and it is on walls that this fern is most frequently found. This fern is sensitive to extremes of temperature and drought so during dry weather the leaves curl up and remain in this position until rewetted.

Current Status

Wall-rue

The Wall-rue is common over the greater part of the British Isles and grows at altitudes from sea level to 1000m. It is perhaps more common in some western and northern districts than in eastern England, partly because of the higher rainfall in the west, but primarily because there are more old stone walls in western districts than in the east. Wall-rue is not directly threatened but is sensitive to atmospheric pollution and scarcer around industrial areas. Wall-rue is infrequent in Hull and is only found on old walls.

Maidenhair Spleenwort

Maidenhair Spleenwort is distributed throughout the British Isles and is known to occur in every county, growing from sea level up to about 800m. It is most abundant in the wetter western and northern parts of the British Isles and is scattered in the east. It is perhaps the most common of the small fern species found on walls and in rock crevices. Maidenhair Spleenwort occurs on walls within the Hull. Although generally rather uncommon it can be seen in profusion on walls in Wensley and Aysgarth Avenues.

Black Spleenwort

Black Spleenwort is one of the commoner ferns in Britain, occurring over the most of the country and is locally abundant in the west. It is absent from some areas in Central and Highland Scotland and the colder rain-shadow east of the Pennines. In areas of low rainfall it is only found on walls exposed to prevailing winds and rarely occurs above 600m. Black Spleenwort is uncommon in Hull, although it does occur in quantity on a garden wall to the north-west of the city centre. Interestingly, this is in the same street as the only occurrence of Rustyback, although not on the same wall.

Hart's-tongue

In Britain, Hart's-tongue is very widespread and extremely abundant in many parts of the country, especially in the west. This is one of the more widely distributed ferns within Hull. Small plants may be found growing on shady walls in many localities scattered throughout the Hull area.

Rustyback

Rustyback is widespread in Britain, but only abundant in areas of high rainfall and therefore shows a strongly western distribution. It is most common in lowland areas to about 200m, although occasionally found at higher altitudes. It is common in SW England and Wales and the Lake District. It is scattered in the Pennines and SW Scotland but very rare north of the Grampian Highlands and east of the Pennines in England. This fern is not threatened in its native habitats but is vulnerable to rebuilding of man-made walls and buildings at the edge of its range. Rustyback had been thought to be extinct in south-east Yorkshire until a small colony was recently found on a garden wall to the north west of Hull city centre. The colony currently contains about 10 small plants distributed on either side of a low wall.

Current Factors Affecting Wall Ferns 

• Many of these fern species are not under threat in their natural habitats but are being lost within urban areas. Many old buildings or walls that support these plants are lost due to redevelopment and others are re-pointed to make them look 'tidy'.
  
  
• People often remove ferns and other plants from walls because they are thought to cause damage. The damage that plants can cause to walls is poorly researched. Woody species, if allowed to grow to any size, can force blocks apart so the removal of trees and shrubs is sensible. Some long-lived perennials may slightly disrupt stonework if growing over a long period of time. However, small herbaceous species with soft stems, such as ferns and a range of other wall flowers can not break down walls. All are picturesque species that should be left to decorate walls, provide local character and soften these otherwise hard landscape features.
  
  
• Air pollution in urban areas, particularly areas supporting heavy industry, may limit the growth of wall ferns.

Current Action

Legal Status

All wild plants are given limited protection under UK law. Under the Wildlife and Countryside Act (1981) it is illegal to uproot any wild plant without permission from the land-owner or occupier. The Countryside and Rights of Way Act (2000) has increased the penalties for offences against plants so that they are sufficiently high to act as a deterrent.

Wall ferns often appear on old buildings, many of which will be 'Listed Buildings' and therefore require special consent before demolition.

Management, Research and Guidance

Over the period of 1998 to 2000 the members of the Hull Natural History Society undertook a project to map the distribution of plants within the Hull area. Distribution maps have been produced for most of the plants found in Hull including ferns.

Action Plan Aims 

1. To undertake a survey to determine the botanical interest of the walls within the City.
2. To encourage people to consider the vegetation on walls as an asset, having conservation and amenity value.
3. To encourage those responsible for wall maintenance to restrict spraying and weeding to those species likely to harm masonry or obscure important details.
4. To ensure re-pointing work is carried out around desirable wall plants.
5. To ensure liaison with KuHCC Development Control and Building Conservation Officer to ensure protection of fern habitat and explore the possibility of habitat development.

What We Are Going to Do

What We Can All Do

• Don't remove ferns or other non-woody plants from walls.
  
  
• Let the Hull Biodiversity Partnership know if you have ferns growing near you.
   

Links With Other Action Plans

Management of The Built Environment and Industrial Land will affect Wall Ferns. Lichens are often found in similar habitats and may benefit from management for wall ferns.

References

Brightman, F.H., Nicholson, B.E. (1985) The Oxford Book of Flowerless Plants. Peerage Books, London.

Dony, J.G., Jury, S.L., Perring, F.H. (1986) English Names of Wild Flowers. BSBI.

Gilbert, O. (1996) Rooted in Stone: The Natural Flora of Urban Walls. English Nature. Peterborough.

Jermy, C., Camus, J. (1993) The Illustrated Field Guide to Ferns and Allied Plants of the British Isles. HMSO, London.

Middleton, R. (2000) The Plants of Hull: A Millennium Atlas. (Retrieved January 2002, from http://www.hull.ac.uk/hullflora)

Taylor, P.G. (1960) British Ferns and Mosses. Eyre and Spottiswoode Publishers Ltd, London.