Trees of Sanctuary

…the only problem is, I’m struggling to decipher it. I peer at the pale green lichen with my hand lens up to my eye, like some monocled Victorian naturalist. Unfortunately, I do not also have the all-round identification skills of the hobby naturalists of those days. Lichens have pretty much completely passed me by for the last forty or so years, so I am struggling here, but this is supposed to be an easy lichen to identify; a good ‘first lichen’. It has characteristic, raised, black markings which are said to resemble hieroglyphs or little bits of writing, Its name, Graphis scripta, reflects that, but whatever this lichen is trying to tell me, it is not written in English. I revert to my usual method of information gathering and go and pull my old text books off the shelves.

At a glance, lichens look pretty nondescript, so I wasn’t expecting to find out much of interest. But suddenly, I was strangely intrigued by these patches of colour on the trees and rocks of the wood. How had I missed the power struggles, imprisonment and possible slavery going on all around me? The details of the lichen’s life came as a surprise; I had completely overlooked the fascinating story unfolding in each minute growth of lichen, and now I had my eye-in, it was clear I had also failed to notice just how much lichen is growing in the wood. Perhaps that Graphis scripta was telling me to pay more attention, to look a little closer.

The basic fact that I had remembered from fleeting mentions in the odd evolution lecture, was that lichens are not single organisms. They are composite organisms, made up of an alga (a very basic plant)¹ and a fungi (a spore² producing organism) growing together. Lichens are described as living in a ‘symbiotic’ relationship – two species living together in an intimate association – but although lichen is often used as an example of two species living together to the benefit of both, this interpretation is now hotly debated by lichenologists. And this is where it gets interesting.

When you look at a lichen, it is the fungal partner that you are seeing; the algal partner is hidden away inside, growing as a thin layer of cells. In the fungus-alga relationship, the fungal partner provides the house, the algal partner provides the food. Fungi can’t generate their own sugar – they usually have to break down the waste products and remains of other organisms so are restricted to environments where this food is available. With an alga to manufacture and supply sugars however, a lichen forming fungus is able to live in places few other fungi could survive – bare rock and tree trunks for example. In return for its food donation, the fungal partner supplies the algal partner with optimal living conditions – protection from drying out, damaging UV rays and grazing herbivores, and an improved supply of minerals that the fungal partner is able to absorb from rainwater and air. The algal partner too is able to live where independent algae could not.

So, win-win all round… except that it isn’t. The algal partner does not gain in the way that the fungal partner does. There are approximately 28,000 species of identified lichen around the world, and so far, there is possibly one known example of the fungi involved being able to survive in nature without the algal partner. There are around 100 known organisms that fulfill the role of algal partner across all of these 28,000 lichen – the vast majority are able to live perfectly happily without the fungal partner, and in fact, do much better on their own. Once captured by a fungal partner, the algal partner is locked into a lifetime of servitude, with at least fifty percent of the sugar it produces being converted immediately by the fungal partner into a form that the algal partner cannot use. The algal partner’s reproduction is limited too. So, when we look at a lichen, are we seeing a parasitic relationship instead, one where the fungus subjugates and farms the alga? The argument rages in scientific circles, but I’ll never look at a lichen in the same way again.

Because of the fungi’s reliance on the alga in a lichen, reproduction poses a problem too. In those lichens that reproduce through spores, it is the fungal partner that produces the fruiting bodies; few lichens are able to produce spores that include the algal partner, so unless the spore lands where a suitable alga is present, the spore will never produce another lichen – chances are stacked against the lichen, but amazingly, some spores are successful, perpetuating the lineage. Some lichens have cleverly circumvented this problem by also being able to reproduce vegetatively³ (from broken off fragments, for example), and some rely solely on vegetative reproduction. There are so many details about the biology of the lichen that I find fascinating. However, I fully appreciate that others do not! So I will stop here and recommend those who want to find out more about the lichens, to begin at the British Lichen Society website – they have an excellent summary page (click here), and links suggesting where to go from there.

The reason I started looking at the lichens in our wood is down to Plantlife’s ‘Looking Out for Small Things (LOST)’ project. In the UK we have large areas of Atlantic woodland, tree rich areas characterised by high rainfall, and mild, humid conditions. These areas form part of the world’s temperate rainforest and are internationally important for the lichens, mosses and liverworts they contain. In Britain, Atlantic woodland is found in western upland and coastal areas. Our wood is included in one of these areas.

Standing under dripping trees, on a moss carpet, while walls, trunks and rocks around me are practically invisible under their of blankets of wet, green, I have no issue with the description of our wood as a rainforest, though I suspect we are off the edge of what would technically be identified as one. Regardless, I would definitely like to know how to conserve the small things in our wood. So, now I am wandering round the trees, equipped with clipboard, hand lens and questionnaire, pretty much clueless as to what species of lichen I am looking at, even as to which group of lichens it belongs. Is it crustose? – one which is flat and clinging so tightly to a surface that I’d have to cut some of the surface away to get the lichen off – or is it fruiticose? – growing upright or hanging from a branch or rock. And why is that different from foliose? – looking like leaves with hanging lobes that can be lifted from the surface on which they grow. I give up for now, and instead just look. There is so much to see – different colours, different textures, different forms. Suddenly I am seeing lichen all over the place and I don’t have to be able to identify it to enjoy it. I can marvel at the fact lichens grow only 0.1 to 10 millimetres per year, so can be used to date things such as the Easter Island statues. I can be impressed that they are so efficient at absorbing inorganic nutrients from the atmosphere, including atmospheric pollution, that they can be used as accurate indicators of air pollution.

And another thing for which there is no need for me to actually identify lichen is  Plantlife’s survey on our woodland. The questionnaire is very easy; it doesn’t involve being a lichen expert, or carrying around testing kits which include carcinogenic chemicals to carry out tests on particularly hard to identify specimens. Instead, it is a survey which assesses the quality of the woodland; it means there can be a targeted effort to conserve the best habitat and manage woodland to maximise the chances of survival of the small things. It sounds like a good plan to me.

So, here’s to our next family project – surveying the wood. Whatever we find, we will be working in the woodland we have grown to love. The aim is to have fun together, learn together and make new discoveries along the way. And if it all contributes to the understanding and conservation of the woodland, so much the better.

I wonder what stories my children will translate from the writing on the trees…

Footnotes:

For some photographs of the lichens we have found at the wood so far, click here.

You don’t have to have to own a woodland to do the LOST survey – if you are out in any woodland over the next year, and it is in the area being targeted, you can fill in a rapid woodland assessment form – it just takes an hour. You can find out how by clicking here. Yay for citizen science!

¹The scientist in me needs to add here that sometimes a cyanobacteria is the partner of the fungi, rather than an alga, but the principle is the same. (A cyanobacteria is a type of bacteria which can derive energy from the sun like a plant.)

²Spore – reproductive unit able to give rise to a new individual.

³Vegetative reproduction – reproduction by asexual means.