Lichen Survey - 12th November 2012
Professor Mark Seaward of Bradford University undertook a lichenological examination of gravestones and trees in the Raikes Road Burial Ground, and comparative studies of walls and stonework near it. Natural climatic weathering of most gravestones has been minimal since they are constructed of hard, resilient siliceous stone. Lichen coverage on the gravestones is poor and, with few exceptions, only a few crustose lichen species and algae dominate stone surfaces.
The surfaces of most vertical gravestones appear to be stable and no lichens noted for their ability to generate chemical disturbance (biodeterioration) recorded. With few exceptions, the apices of the vertical gravestones lacked the lichen flora normally expected. Only one gravestone supported foliose (leafy) lichens (Melanelixia fuliginosa and Parmelia saxatilis) on the apex, and a further had remnants of P. saxatilis thalli.
Most gravestones are aligned east–west as usual, and the contrasting lichen flora normally found on eastern and western faces of gravestones (with essentially shade-loving species, Psilolechia lucida and Lepraria incana, on the latter) was evident. The gravestones in general were poorly colonised by lichens with no more than five or six crustose species, as well as the two foliose species (see above) present. No rare or unusual lichens were noted. A few splashes of white and green of different hues generated by lichen thalli were found throughout the site. It should be noted that the mosaic generated by the lichens is a standard ageing feature on historic monuments, and is generally regarded a ‘patina of time’.
The burial ground contains an interesting variety of conifer and deciduous trees of varying ages. The trunks of these trees support a limited lichen flora, but many of the twigs (not acidified due to air pollution in the past) support a diverse lichen flora (9 species) including colourful foliose Xanthoria (orange) and Physcia (grey) species.
Chemical treatments (e.g. fungicides and herbicides) of stones and vegetation should be discouraged. If selected tree felling is necessary, consideration should be given to retaining the stump and/or a log on site. One such extant stump supported the only lignicolous lichen (Cladonia cf. coniocraea) noted in the burial ground.
The lichen flora of the siliceous gravestones in the burial ground is representative of most graveyards dominated by siliceous stones throughout the region. It should be noted that its saxicolous lichen flora is as yet barely influenced by nitrogenous products, although this is a possibility for the future, as noted on the trees (see above). This phenomenon has proved to be the over-riding factor responsible for recent, often highly aggressive, nitrophilous lichen assemblages dominating large areas of Britain; this trend needs to be monitored at the burial ground.
The original report including general discussion on the flora and enviromental management is available for download.