Listening this morning to Jim Al-Khalili’s series on Radio 4, The Life Scientific, in which he talked to botanist Pat Wolseley about her obsession with lichen and the environmental secrets it holds, I thought of the many times I had photographed lichens in different parts of the country, struck by their beauty with the appearance of an abstract painting.
Jim Al-Khalili discussed with Pat Wolseley her work in establishing the Open Air Laboratories (OPAL) network which, since 2007, has encouraged people from all kinds of backgrounds to get back in touch with nature and generate valuable scientific data concerning the state of the environment by monitoring the presence of lichens in their local area.
Lichens are humble and ancient organisms that can offer significant pointers to the quality of air we breathe. So, for the last five years, thousands of people throughout the UK have been gathering scientific data on different lichen populations in their local area and using it to monitor air pollution.
In the programme (one of an excellent series in which Al-Khalili chats informally with a chosen scientist about the research he or she has been engaged in) Pat Wolseley explained that a lichen is not a separate organism but is actually a close partnership between a fungus and an alga. There are more than 1,700 species of lichen in Britain, while approximately 18,000 species of lichen have been described and identified worldwide.
Lichens colonize some of the most inhospitable habitats on earth. They can survive in extremely cold areas such as on high mountains and in regions such as the arctic. They may be virtually the only plant form surviving in some of these areas and can be vitally important sources of food for animals. They are also found throughout less extreme climates, inhabiting just about any solid surface. This can range from rocks on sea shores, to walls, trees and concrete.
Lichens are so enormously successful and widespread because of their unusual partnership. The algal cells, through the process of photosynthesis, provide the fungus with some of the organic nutrients which it needs.
Pat Wolseley’s research, based on the data collected by thousands of volunteers, has revealed a story that is positive: nitrogen-sensitive lichens are on their way back across much of the country, especially in areas that were formerly lichen deserts, such as London and Birmingham. This is most probably because of the decrease in sulphur dioxide pollution in recent years.
However, nitrogen-loving lichens are increasingly widespread in country and urban areas where nitrogen levels are high due to ammonia from intensive farming or nitrogen oxides from heavy traffic. The OPAL data suggests that this is the case on Merseyside: the map below, with its red spots, indicates an area with no or few lichens, typical of agricultural and urban areas where nitrogen levels are high due to intensive farming or pollution from cars and industry.
The reason why lichens are such good indicators of atmospheric pollution is that they absorb water and minerals from rainwater and directly from the atmosphere, over their entire surface area, making them extremely sensitive to atmospheric pollution. As a result, there are usually very few lichens around industrial centres and towns. But different lichen species vary in their tolerance to pollution and therefore make very good biological indicators of levels of atmospheric pollution.
A walk around a local churchyard can often reveal a lot about air quality in the area. Churchyards are usually relatively undisturbed areas, with stone headstones which provide a good substrate for lichens. A good look at these lichens will give an indication of how good the air quality is locally.
Pat Wolseley spoke about the difficulty of making accurate identifications, given all those thousands of species of lichen. There are, however three broad categories of lichen. Crustose lichens are encrusting forms which spread over and into the surface of their habitat. Foliose lichens have leafy lobes, which spread out in a horizontal layer over the surface and are attached by root-like threads. Finally,Fruticose lichens are the shrubby forms with many branches.
The Trouble With Lichen? A science fiction novel by John Wyndham (The Midwich Cuckoos and The Day of the Triffids) first published in 1960, that I read sometime in that decade, along with just about everything else he wrote. The story dealt with the discovery of a rare lichen that slowed the ageing process – so that a human lifetime could be extended to 200 or 300 years. There’s a review by Nicholas Lezard of The Guardian here.