Monday, 15 March 2010

Appreciating Lichens...

...Till there rose, abrupt and lonely,
a ruined abbey, chancel only,
lichen-crusted, time-befriended,
soared the arches, splayed and splendid,
romanesque against the sky....
John Betjeman, Ireland with Emily.

A landscape friend of mine has asked me several times to do something about lichens, which I feel a bit shy about doing.  I am a landscape architect married to a lichenologist.  It isn't often that venturing into subjects that you know many people who know the material better than you do is particularly sensible, so I have resisted her suggestion each time she has made it.  However, lichens are a part of all of our worlds and the international lichen community is in the process of selecting their top 100 lichens.  This has started me thinking about how I would address that as a landscape architect, and not as a lichenologist.  Lichens come in all manner of shapes, sizes and textures.  They grow on all manner of surfaces, which now include my car following a couple of years of dusty summer PM10 deposits building up in crevices of windows out of the reach of the car wash.  Many of the current great lichenologists have a profound love and in-depth knowledge of tiny little dot lichens that most people wouldn't even notice. Landscape architects are more likely to prefer the more showy lichens....  (In fact the emerging list contains many very beautiful lichen species and I will add a link to the full list when it is available in the next few weeks).

The key surfaces upon which lichens grow are: rocks (saxicolous), trees (corticolous), wood (lignicolous), soil (terricolous), moss (muscicolous), other lichens (lichenicolous) as well as leaves (foliicolous) and even metal (metaliferous).  Almost all of these surfaces are ones that we work with in landscape design or management.  Graveyards are the most obvious places where people can see lichens growing and which generate a great deal of reaction to their presence.  Lyrical poetry has been written on the relationship of lichen covering to the concept of age, and occasionally it is linked to the idea of decay, which is not at all fair.  Some churchyards go to extraordinary lengths to 'clean' the churches and memorials of their lichen covering.  It is known for new stones to be polished to resist lichen cover, which is a shame and has given many modern graveyards a stark and aggressive character, with each letter etched deeply and embossed in gold leaf.

In cities such as London, until about 30 years ago, most lower plant cover of monuments, walls and trees came in the form of a dark green alga mixed with soot.  It was ugly and it felt as though everything needed a good wash.  This was due to the very high levels of industrial and coal- based pollution.  It is amazing to consider that in some cities now the air pollution levels have sunk below those of the countryside which is awash with nitrates from fertiliser.  Work being done on air quality by OPAL is showing very clearly the increase in pollution-sensitive lichens colonising urban centres, with decreases also showing in rural areas as nitrate levels increase (more information here).  OPAL is an initiative run jointly by the British Lichen Society, the Natural History Museum and Imperial College, London.

Lichens can give valuable details about the health of an area, urban or rural.  There is a lovely simple grey lichen that can tell if a piece of woodland has been under continuous canopy for over 400 years just by its very presence.  It is highly sensitive to change in management.

There is a brilliant and flamboyant yellow splat of lichen that announces very graphically where birds or dogs have 'been'.  It thrives on nitrates and is also very keen on airborne particles of nitrogen compounds that can build up in the nooks and crannies after a period of dry weather.  This can mean that it will grow on small twigs in preference to the main bark of a tree.  Almost all lichen names are in Latin only.  This lichen is called Xanthoria perietina.

I have had a long affection for and interest in the use of concrete because it is so ubiquitous and flexible in how it can be used.  Different surface textures can be designed into it, but it does have a poor reputation based heavily on the green alga that will grow on it as it ages, dulling a once bright surface, making it appear in need of tooth-whitening techniques.  I believe that it may be possible for us to design in ways to make this work.  In the 1980s there was a short fashion for architects to design their wooden cladding in office atria and the 'reconstructed stone' effect of the buildings' exterior to tie together.  Since this poncy name is basically concrete when used in a fine grain form it is very interesting that the inevitable streaking of the surface came to reflect the grain of the wooden panels indoors.  Some buildings and walls have had pig slurry or other compounds sprayed onto the walls to encourage rapid colonisation by lichens to mellow their look and imply age and robustness.

I have chosen a few lichens to comment further on:

Cladonia stellaris is an arctic species that doesn't occur anymore in the British Isles.  It is eaten by reindeer and moose, and is a major constituent of reindeer moss.  The relevance for landscape, apart from the utter beauty of its form, of course, is the history of its use for architectural modelling.  It is one of only a few species that were used traditionally in the depiction of trees around buildings.  I used to be able to buy bags of it for my college models.  It was often dyed varying shades of green, which softened the normal crunchiness of the growing organism.

A lichen that gets both lichenologists and members of the public equally excited is Lobaria pulmonaria.  This lichen has been given an English name, Lungwort, in the herbal tradition of health-giving properties showing in the visual form of an organism.  It was considered to be a powerful aid in the treatment of lung disease as a result of its very lung-like characteristics.  It is incredibly sensitive to air pollution and occurs in the best quantities in western Scotland and Ireland.  It does occur in pockets in England and is heavily protected by legislation.  In paintings by Constable of trees at Flatford Mill, he shows it as abundant on their trunks.  It has not been seen in East Anglia since the industrial revolution.

A sibling to Xanthoria parietina is Xanthoria aureola.  This is a coastal species also fond of bird droppings etc, but has a different character and form to its more widespread relative.  It is also more likely to be orange rather than yellow.

Many other lichens have siblings with different localities.  Ramalina farinacea is a widespread lichen often seen growing on twigs or fences. It prefers a good air quality.

Ramalina siliquosa, on the other hand, although with a similar form, is far more fussy.  Not only does it require good air quality, but it really needs that air to be salty and is another lichen with a range that is primarily coastal.  Strangely, it does grow on Wiltshire Sarsen stones, a fact that has not been easy for lichenologists to explain.

And finally....

When picnic tables come towards the end of their useful life it is not everyone who shuns them, by any manner of means.  As they age, their lichen community increases and so does the community of lichenologists who enjoy them.....

as well as having their own way of showing appreciation of paving...the next photograph was taken by Simon Davey on a field visit to the Netherlands.

For further information – the obvious site from which to begin - The British Lichen Society

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