9 December 2016

I'm 'lichen' it - plenty to see on winter walks

With winter tightening it's grip it can feel like the whole of nature has hunkered down until spring and there's not much out there to appreciate. That’s what can make winter the ideal time to build an appreciation for some of the less dramatic lifeforms, the ones you might overlook in the more fecund months of the year. Ladies and gentlemen, I give you the lichens.

In fact, given that lichens cover (by some estimations) some 6% of the earth’s surface, overlooking them is something that we probably all do a lot of the time. If it wasn’t for the clean air act then this is something most town dwellers would have been forgiven for as lichens are a great indicator of air pollution – they don’t grow well in polluted environments. But nowadays they can be found almost anywhere, although admittedly you’d need to go to some of the more remote parts of northwest Scotland to see the best examples.
Cabbagey! A very leafy Foliose (see below) Lichen on a tree near Aira Force
But what is a lichen? Well, it’s complicated. And also a bit weird.

Simply put, they are composite organisms. This means they are neither one thing or another, but more a new kind of life form that arises from (mostly) an algae living amongst the filaments of a fungus in a symbiotic relationship. The algae benefit by being protected from the environment by the filaments of the fungus, which also gather moisture and nutrients from the environment, and (usually) provide an anchor to it. The fungus benefits because the algae produces food by photosynthesis, something they are unable to do.
Some lovely hairy Fruticose (see below) lichens on a tree
They’ve been recognised as organisms for quite some time but it wasn’t until 1867 when Swiss botanist Simon Schwendener proposed his dual theory of lichens that their true nature began to emerge. However, common censunsus at the time was that all living things were autonomous so this was rejected at first (it seems the composite organism thing was just too strange) and it took many years and the support of high profile people, including our very own Beatrix Potter, to finally see the idea accepted.

Nowadays, the arguments still go on. At the moment they are classified by their fungal component, but there is some debate over whether this is the right thing to do as two dramatically different looking lichens can be technically the same thing due to having the same fungus but two different algal parts. Confusing!
Beautiful patterns on a Crustose (see below) lichen on one of the walls at High Wray Basecamp volunteer centre
In fact, once you start to look into them it gets extraordinarily confusing with identification being a really specialized field requiring microscopes and chemicals. But this doesn’t need to take away from the fact that with a little knowledge and open eyes they can add an extra element to any winter walk.

A good starting point is to get to know the three most commonly accepted growth forms: Crustose (like a crust), Fruticose (like a little shrub) and Foliose (with leaf like structures). There are lots of others and the boundaries between these are sometimes blurry but get a cheap hand lens and go in close and you’ll be amazed at the microscopic and very alien world that is right there under your nose.
Bright red 'podetia' seen on some lichens, bearing spores 
Finally, here’s some  Fun lichen facts!

Unlike simple dehydration in plants and animals, lichens may experience a very high loss of body water in dry periods. Lichens are capable of surviving extremely low levels of water content (poikilohydric). They quickly absorb water when it becomes available again, becoming soft and fleshy. That’s tough!

The European Space Agency has discovered that lichens can survive unprotected in space. In an experiment two species of lichen were sealed in a capsule and launched on a Russian Soyuz rocket in May 2005. Once in orbit, the capsules were opened and the lichens were directly exposed to the vacuum of space with its widely fluctuating temperatures and cosmic radiation. After 15 days, the lichens were brought back to earth and were found to be in full health with no discernible damage from their time in orbit. That’s tougher!

Lichens are a pioneer species, often the first to colonize bare rock. They can grow in a very wide range of environmental conditions and can grow on almost any surface. They can even live inside solid rock, growing between the grains. Also quite tough …..

When growing on rocks some lichens slowly decompose them, contributing to the process of weathering by which they are turned into soil. Normally benign, this can cause a problem on artificial stone structures such as Mount Rushmore in the States which has to be regularly cleaned of Lichens. So tough even the might of the US struggles against them!

By Rob Clarke, Ranger at High Wray Basecamp volunteer centre

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