Lichens are curious dual organisms, a symbiotic association between a fungus and an alga. Although the alga can often live successfully on its own, the fungus cannot survive without incorporating algal cells into its tissues. In some ways lichens are incredibly hardy; a specimen of the common leafy orange lichen (Xanthoria parietina) was taken up and placed outside the International Space Station and spent ten days in the high vacuum of space, bombarded with cosmic rays and subject to extremes of temperature. On its return to Earth it revived and continued to grow. On the other hand lichens can sometimes be very sensitive to environmental factors. Much of the Midland area of England became a “lichen desert” due to high levels of atmospheric sulphur dioxide pollution from the Industrial Revolution through until the 1970s. The level of sulphur dioxide has now fallen below the level where it is a limiting factor for lichens and we are in the middle of a spectacular (but mainly unnoticed) re-colonisation. Some of the lichens involved in the new communities are species that were unknown before the 1980s. Bacidia neosquamulosa is present on the base of an ash tree in Bedford Cemetery; it was described as new to science in 1999 and has become frequent across Western Europe in the past 10 years.
Anaptychia ciliaris subsp. ciliaris (called “Devil’s claws” by some) has recently been found on a gravestone in the cemetery. There is an old record for this lichen from Woburn Park but it was feared that this species, which has drastically declined across lowland England, was long-extinct in Bedfordshire. To reflect the fact that this species has declined so rapidly it has been designated as an endangered species in Britain.
Not far from the chapel there is a wonderful old table tomb capped with a large sandstone slab. This supports Buellia badia and Stereocaulon pileatum which are not known from any other sites in Bedfordshire. An oak branch in the cemetery supports a community of yellow lichens composed of several species which are favoured by the modern atmospheric pollution regime – that of compounds of nitrogen which arise from burning fossil fuels and the use of chemical fertilisers on a landscape scale. Candelariella reflexa used to be a feature of the “canine zone” of tree trunks (the lower part visited by urinating dogs) but the landscape is now so nutrient-enriched that this species now thrives on branches; in Bedford Cemetery it grows with Candelaria concolor (from a largely sub-tropical genus which may be spreading north due to global warming) and Xanthoria ulophyllodes (its first recorded occurrence in Bedfordshire).
The vast majority of the conspicuous lichens present in Bedford Cemetery are common species which, nevertheless, create beautiful patterns of colour on the gravestones. The most important memorials are now recorded to prevent inadvertent damage to the rarer lichens. This report was submitted by a member of the Friends, Mark Powell, who is also a member of the British Lichen Society.