Gardens contain a wide range of substrata and microhabitats and thus tend to support a relatively large number of lichens per unit area. The majority of lichen species occurring in gardens are common species associated with relatively recent structures and relatively young trees. Gardens containing older structures and trees, especially if they are several centuries old, are more likely to contain notable lichen species. The geographical location of the garden will have a significant bearing on the lichens which are present.
Lichen diversity in gardens – some case studies
1. An overview of English gardens.
Allen & Hilton (2011) reported the results of a British Lichen Society project in which 45 gardens were studied as the Society’s contribution to the International Year of Biodiversity. Results from the survey indicate that:
the South-West provided the highest diversity of lichens reflecting the high rainfall and generally good air quality of that region.
the Midlands followed closely, its strength being saxicolous species.
Garden size is an important factor, larger gardens providing more scope for a variety of different features. Nevertheless some notable records came from smaller gardens.
Thatched roofs provide a refuge for heathland lichens while smaller features, including a canvas chair and Rhododendron leaves support interesting communities.
Paving, fruit trees and old brick walls were especially rich in species.
2. Caloplaca demissa
The British Lichen Society was allowed access to the gardens at Highgrove in Gloucestershire during August 2010. Along the edges of the Thyme Walk are set some massive terracotta urns on which most of the lichens present are common species similar to those found on brickwork or sandstone headstones. One minutely lobed crust was collected and subsequently turned out to be the first, and so far, only record of Caloplaca demissa in the British Isles.
3. Caloplaca calcitrapa
The magnificent house and gardens at Cliveden in Buckinghamshire are now owned by the National Trust. Two separate balustrades are present along the south side of the house, the most spectacular of which is the early seventeenth century Borghese Balustrade which was purchased by Lord Astor in the late nineteenth century from the Villa Borghese Gardens in Rome. Extensive restoration work was being undertaken to the terrace and balustrades during 2012 and a survey was commissioned in case any notable lichens needed special consideration during the works (Powell & Vondrák 2012). An unfamiliar specimen of Caloplaca was collected from the newer balustrade and this subsequently proved to be the first, and so far only, occurrence of Caloplaca calcitrapa in Britain (an enigmatic record since this is considered to be a species restricted to the Mediterranean basin). The Borghese balustrade was situated in Rome for more than two centuries, and was probably covered in Mediterranean lichens at the time of transfer to England. This may be the source of the C. calcitrapa and provides an interesting and rare example of a potentially introduced lichen community.
4. Whipsnade Tree Cathedral
Punctelia reddenda is a large leafy lichen, generally thought of as an ancient woodland indicator, usually growing on the mossy trunks of broad-leaved trees in the south and west of the British Isles. It was discovered on a softwood fence surrounding the Whipsnade car park (Powell 2011). Its appearance here in Bedfordshire is remarkable for two reasons. Previously it was unknown from anywhere in East Anglia, the Midlands or the south-east of England north of London. Even where it does grow (and nowhere is it a common species) a rotting fence rail would be considered an unusual substrate.
This post and rail fence was due for imminent replacement but, alerted to its importance, the National Trust came up with an elegant solution. The old fence was retained in situ and a new supporting fence was constructed using untreated softwood. The lignum of fences is often found to have particularly interesting lichen communities and in the case of this habitat notable species can colonise relatively quickly.
The oldest features such as old walls, ornamental features and any ancient trees are more likely to support important lichen communities than recent features. Exceptions to this general rule include fences, shingle roofs and thatch.
Consideration should be given to the potential harm to lichen communities if restoration or relocation of old features is contemplated. Ideally an experienced lichenologist should be consulted to conduct a survey beforehand.
In general ivy should be prevented from colonising new areas of stonework because its dense shade smothers lichen communities.
There is a limited but interesting community of lichens which can grow on the surfaces of evergreen leaves. The study of these lichens provides a fascinating project which will transform any visits to gardens or parks. It is likely that foliicolous species are responding to changes in atmospheric pollution and to climate change and any records will provide useful scientific information. Here are a few examples of the type of things found in the Midlands (probably the poorest region) in the last couple of years:
- Phylloblastia inexpectata has been recorded with some frequency on holly, Rhododendron, ivy and other leaves in parks, gardens as well as old woodlands.
- Phylloblastia fortuita was first discovered in Britain in 2007 (before it had been named as new to science) and has since then turned up at several sites including shrubberies in Cambridge University Botanic Garden.
- Scoliciosporum curvatum was found on holly leaves in Sutton Park, within seven miles of the centre of Birmingham.
- Fellhanera bouteillei turns up from time to time on box and yew hedges.
Allen, A. & Hilton, B. (2011). Lichen diversity in gardens. Bull. Brit. Lichen Soc. 108: 11-32.
Powell, M. (2011). Lichens on softwood fences, some remarkable records and a happy ending. Bull. Brit. Lichen Soc. 108: 6-7
Powell, M. & Vondrák, J. (2012). Italian balustrade at Cliveden hosts Italian lichens? Bull. Brit. Lichen Soc. 110: 11-14.