Monkton Rectorial Benefice - The Stackpole Lichens

What are lichens?
Lichens are an example to us all in getting on well together. They are actually not a simple organism at all, but two quite separate organisms (an alga and a fungus) living symbiotically, in harmony together, and depending on each other.

There are 1608 known types of lichen in Britain. Some prefer woodland, some coastal cliffs, some heathland, etc. They even have preferred types of stone, and locations in the weather, so it is perhaps surprising that nearly 600 of these known examples are found in churchyards.

They are often the richest habitats for lichens. Some in fact do not occur anywhere else but in churchyards. After all, many churchyards have been around for hundreds of years, and have been very largely undisturbed, apart from essential tidying. Lichens would appear to require four things of a stone. In the first place, initial colonization is made easier if its texture is sufficiently rough for propagules to attach themselves. Secondly, as lichens are slow-growing and long-lived, they also require a durable surface. Thirdly, it helps if the stone is sufficiently porous to take up water. Lichens have the ability to absorb minute particulates from the stone which either inhibit or encourage growth and reproduction. Fourthly, many lichens are precise in their ecology, the pH and chemical composition of a substrate have a major influence on what may grow on it.

One of the most important regional factors is the availability of suitable building stone. A good local source is an immense asset in providing materials for the church itself, the boundary wall and the older tombstones. While some prosperous parishes have imported high-quality stone from elsewhere, there is often a link between the solid geology and the materials used in any area. These, in turn, play a major part in determining species presence, dominance and diversity and the degree of surface coverage.

Small, inconspicuous lichens are likely to be the first to appear, but by their great numbers they can quickly soften the colour of a harsh surface. These are normally followed by larger, grey and orange, lichens that will in time give a wall an attractive weathered appearance. If this surface is, by some means, nutrient enriched this will encourage the large orange, leafy lichens (Xanthoria species) and also a number of grey species (eg Diploicia canescens). Lichens are, by their nature, not very startling or spectacular. They are typically the plate-sized blotches of grey, green or orange on old stonework and trees that are such a feature of old and undisturbed structures.

In Stackpole they are most conspicuous on the gravestones of the old part of the churchyard, and the outside walls of the Church itself. At the same time, the lichens on the trees, should not be overlooked. They are apparently among the rarest specimens in the churchyard.

Each lichen has its preferred habitat. Most of them have long and unmemorable Latin names, like the two illustrated in this article. A few however do have more recognisable English names. There is one conspicuous grey-green lichen, for example, on the south wall of the Church (just beside the path leading to the porch) which has a distinctly knobbly effect in the centre. These are the fruit bodies, and because of their appearance under a magnifying glass, it is known by the curious name of Crab's Eye Lichen. Some lichens like a well protected position, out of the weather. A good example of this in Stackpole is the bright green lichen on the inside wall of the lychgate opposite the porch. It can also be found on parts of gravestones with a good overhang. Other lichens colonise the top of gravestones, because they take nutrients out of the bird droppings there. There is even one odd lichen that actually thrives on the metalic drippings from the grills protecting the windows. Others are so small that you need not only a good magnifying glass to see them, but also to know where to look for them - often in little crevices between stones, for example. For those who take lichen spotting really seriously a good x10 magnifying glass is an essential part of their equipment.

Why are lichens important?
A number of scientific surveys have shown that lichens thrive in areas of clean unpolluted air. The quantity and quality of lichens in a particular site are therefore a simple, natural indicator of the air quality in the area, without the need of expensive and complicated scientific monitoring instruments. They are, if you like, nature's own, simple but effective, monitoring equipment.

Why are the Stackpole lichens so good?

There are 160 different species of lichen in Stackpole churchyard, as the below extract from the British Lichen Society Bulletin indicates. This is the greatest number, to date at least, of any churchyard in Great Britain. There are clearly many reasons. Stackpole churchyard is very old, going back some 700 years, during which time it has been very little disturbed. Furthermore, it is in a sheltered spot, down in the valley, with a good variety of surrounding woodland and stone types. (The church itself is made of a mixture of red sandstone and lime stone, for example). In addition to these factors, Stackpole is near the coast, and some lichens are only to be found in coastal areas. Finally, and very importantly, South Pembrokeshire is still in a clean air area. The prevailing winds, from the South West, have travelled across the Atlantic, with virtually no contact with mankind.

Extract from British Lichen Society Bulletin No 77 (1995)

(Reproduced by kind permission)
All three main BLS field meetings this year are in Wales and, as I write, I have recently returned from the second, the Cladonia Workshop at Orielton in Dyfed (now Pembrokeshire again). By way of a change, it was decided to spend some time on the Monday in a nearby churchyard and, after some deliberation and poring over maps, Stackpole Elidor was chosen.

It was a wise choice. Although not large, the yard was on a steep, south-facing valley slope and sheltered, though not excessively shaded, by sycamore, holm oak, ash, cherry and a single yew. It had most of the credentials - boundary and retaining walls, two wooden gates (one a lych), a somewhat irregularly shaped fourteenth century church with a deeply shaded enclave on the south side, some accessible roof slates and some copper run-off. The building was constructed of a fairly haphazard mix of Carboniferous Limestone and Old Red Sandstone.

The memorials were likewise variable; in age, geology and design. There was even an old rugged cross with a sufficiently large stepped base for us all to sit round and eat our packed lunches. The vicar's wife who appeared later said that, had she known we were coming, she would have opened up the village hall and provided us with cups of tea.

The expertise of Peter James naturally was in great demand and he was harried from pillar to post. one minute it was Verrucaria dufourii found by Steen Christensen from Denmark at the base of a headstone and the next Verrucaria caerulea at the base of the aforesaid cross. It was soon clear that the stones were providing a goodly list and the trees augmenting it most satisfactorily. We were well in excess of 100 species.

After dinner, back in the workroom and, with much help from Trevor Duke and Brian Fox, I was able to TLC some sterile, powdery crusts and turn them, as if by magic, into Lepraria lobificans and Leproloma diffusum. Meanwhile, Neil Sanderson was examining the spores of black dots on twigs and announcing species such as Eopyrenula grandicula and Leptorhaphis maggiana that I had never even heard of let alone found in churchyards before!

On retiring somewhat belatedly for the night, I was pretty sure that, on 4th September 1995, we had found a churchyard richer in species than any other so far in Britain. On the following Wednesday, prior to setting out on my homeward journey I couldn't resist yet another look and managed to add four more common saxicolous species missing from the list, including Lecanora conizaeiodes (rare in these unpolluted parts), and Cladonia chlorophaea (ironically for a Cladonia Workshop) missed by us all two days before. While I was there, Neil also reappeared and added three more epiphytes. The next Sunday, having examined all his packets, he phoned through five more, including two more Opegrapha species making no less than ten in all. With some determinations still to be made, the total already stands at a magnificent 160.