Partnership and colonial habitats in the cemetery
In addition to the abundant plant habitats Heene Cemetery has graves of a variety of materials and designs that serve admirably as suitable places for wildlife to colonise. A single grave with headstone, and perhaps with one or more of stone kerb sets, memorial ledgers, cremation memorials, or other associated stonework has several adjacent habitats because part of it will be in sun, part in shade, at different times of the day and in different seasons. Run-off water creates damp areas to contrast with dry, well-drained areas. You may see sedges and mosses growing in the damp spots and grasses in the dry spots. Different mineral structures that have been used in the construction of graves have different porosities and will retain different degrees of moisture content and lose it at different rates. Stonework ages and weathers, some to a greater extent than others, and microorganisms of numerous types will occupy the irregularities created and become food chain starters. A grave is thus a mini-ecosystem whose individuality should be recognised during any essential maintenance. The component microorganisms, plants and animals of this mini-ecosystem reveal themselves and their habitat preferences by the areas they have colonised, and if you regularly visit or work on a particular grave please take the trouble to inspect and remember what is normally to be found in particular locations upon it so that you are aware of what habitats and their occupants are present, and which therefore need to be respected, managed and preserved.
Minerals used in the construction of headstones and other parts of graves
Headstone materials in the cemetery are of two types, acidic and alkaline.
Acidic stone types
These are predominantly granite, slate, and sandstone, and generally attract foliose lichens and some crustose lichens. Lichen growth characteristics will be explained below.
Granite is a strong, resilient stone, which comes in a variety of colours, and resists weathering very well. It needs no more than cleaning with a soft brush and then a damp cloth.
Slate is a tough, smooth, and long-lasting stone if looked after, but it is slightly porous and can become delaminated. It is easily scratched but is not prone to staining. Just a cloth is needed to clean it.
Sandstone is finely textured but is porous and easily stained. Not being a tough material lettering has to be bold and deep, and is best sealed after engraving. Sandstone needs careful cleaning with soapy water.
Alkaline stone types
Only marble and limestone are commonly used. They frequently have orange crustose lichens.
Yellow Scales (Xanthoria parietina), Heene Cemetery, September 2020
Geologically marble is recrystallised limestone and is smooth with a range of colours and also different veins of colour. It is prone to staining and does not age well, especially in a damp or wooded area, and in urban locations where it is exposed to acid rain.
Limestone is prone to weathering and discolouration but over time it does harden and mellow. Lettering needs to be bold and deep, and then sealed. A soft brush followed by distilled water are used to clean this stone. Proprietary cleaners are often slightly acidic so should never be used on alkaline stone, and are best avoided on acidic stones too.
The same care should be taken with other parts of a grave’s construction, especially any kerb sets (usually strips of stone in a rectangle around the grave), memorial ledgers (stone slabs that lie flat on top of graves), and the various designs of cremation memorials, which are often in the form of flat tablets with a memorial such as a vase or other flower-holder.
Fungal partnerships
The role of fungi in the natural world is a good example of dependency. Whereas all green plants and certain bacteria can manufacture carbohydrate from atmospheric carbon dioxide, fungi, being descended from the animal genetic line, cannot make their own carbohydrate. Therefore, fungi can only survive in association with other organisms, living or dead, that can supply them with carbohydrate. We have fungal populations permanently inside our own bodies, and the same applies to every plant and animal in the cemetery.
Lichen (Lecanora Dispersa), Heene Cemetery, July 2021
Fungi must be treated with the utmost care because other organisms will depend upon them. As the association of fungi with plants is often symbiotic (of mutual benefit) it is essential that soil disturbance in the cemetery is kept to a minimum so that the network of subterranean fungal bodies is not disrupted, as this can seriously reduce the vitality of dependent plants, and with it the cemetery’s biodiversity. The association of fungi with bacteria or algae is the basis for lichen biology, and cemeteries are among the best places in any locality to see a range of lichens. Heene Cemetery is no exception. There are about 2,000 lichen species in the UK of which a third are known from their presence in cemeteries.
Lichens
Lichens are an association of fungi with either green algae (85% of lichen species) or Cyanobacteria (15% of lichen species), and the cemetery has a varied collection of these fascinating and beautiful duos. The algae and Cyanobacteria produce carbohydrate by photosynthesis, which the fungal component of the partnership needs. Headstones with lichens attached should never be cleaned, as lichen growth can be ancient and fragile, and may not re-establish in today’s polluted urban environment. Colours of lichens vary, but when wet many will become translucent and if one component is a green alga that lichen will appear green.
Three lichen types are commonly found in cemeteries:
- Crustose lichens are characterised by being firmly attached to stone. Leprose crustose lichens have a minute globular structure and placodioid crustose lichens have lobes on the margins.
- Foliose lichens are easily lifted and frequently attached by root hairs. They have a leaf-like appearance. Owing to their fragility they should not be touched.
- Fruticose lichens have a bushy, branch-like structure.
Yellow Scales (Xanthoria parietina), here growing on Hawthorn (Crataegus monogyna), Heene Cemetery, December 2021
Lichens grow slowly, sometimes as little as half a millimetre a year, and can be long-lived. Growths of lichens cause virtually no damage to stone, and a good covering of lichens may even protect it. The different meteorological and geological aspects of a headstone, its different weathered textures, the recesses of lettering, sills stained with iron or copper fittings, and the presence of granite chippings, mean that several types of lichen may be growing on it. Grave lichens should be considered as part of the grave itself and carefully protected.
The Field Studies Council publishes excellent guides to lichens, which may be purchased from its website.
Written by Brian Day