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new lichen

PostPosted: Sun Apr 27, 2014 9:08 am
by GregLee
This wall is 5 or so years old now. Recently we have had a run of wet, mild weather and now lots of little colonies of lichen have appeared on the wall. It shows what my life is like that I am quite excited by this. In a few years I might have a good covering of lichen.
It's interesting that lichen germination events only happen rarely in my hot dry climate, there is lots of lichen around but it takes a long time to get started in new stonework. Stones only a couple of years old didn't get any lichen started on them..

Re: new lichen

PostPosted: Thu May 01, 2014 5:50 am
by Tracey B
Nice find Greg. Why wouldn't you be excited? Lichens are unique and fascinating organisms, although not everyone would share our mutual interest. But for their information I would add that scientists more or less agree, lichens are a fungus together with one or more algae living in a symbiotic relationship to form a stable and identifiable body.
A churchyard in Dorset holds the current UK record for the number of species found on one site, 170.
I have a book on them so would suppose I qualify as a lichen geek.

Re: new lichen

PostPosted: Thu May 01, 2014 7:29 am
by GregLee
I was in dorset/somerset last year, this is a photo I took of a churchyard near crewkerne. The wildflowers were amazing, primroses, anemones etc. I can believe there would be many species of lichen.

Re: new lichen

PostPosted: Sun May 04, 2014 7:35 am
by CarolJane
This is very interesting to me,
Im studying with the Open University doing environmental science and i have a project to do.
After my tutor rejectied my original idea, i came up with a new one....
does the direction in relation to the sun affect the growth of lichen on dry stone walls, i live near the Dales so i`ve plenty to look at!
My tutor wants me to look at `different types` of stone walls, i didnt realise there were `types` so i started to look for information on what sort of stone is used?
im guessing its whatever is in the area?
But then i find this discussion...well im excited now!

I have a lot more research to do on `types`
any hints and tips greatfully accecpted!

ps...thanks for having me

Re: new lichen

PostPosted: Sun May 04, 2014 2:25 pm
by jerryg
The direction of the sun definitely seems to effect the kind of lichen on walls, and so probably does the type of stone in the wall. Up here in the Lake District most of our walls have a different type (colour) of lichen one side to the other of the same wall.

The type of stone in the surrounding landscape defines what a wall is built of. For instance if you go somewhere in the Dales where the landscape changes from gritstone/sandstone to limestone you will usually find a piece of wall where at one end is built with sandstone and the other end limestone, and somewhere in between will be a mix of both. Possibly you might check the walls that go up the hills around Penn-y-ghent which from memory changes from limestone in the valley bottom to gritstone higher up.

There are definite examples of this in the roadside walls around Kirkby Lonsdale to Hutton Roof . You will probably find similar examples all over the place.
I think it would be of interest to the members of this site if you were to find out how the lichen changes both with respect to the weather and the type of stone.

Up here nearly every wall we have changes stone not only from valley to valley but from field to field. I assume that the lichen changes too, certainly the colour of the face of the wall does. We often have a mossy side and a lichen side. Whenever I repair an old wall where-ever I am working, I always endeavour to rebuild each side of the wall with the stone that resembles each side of the existing wall. I think most wallers who have a feel for the work, probably do the same.

Happy stone hunting.

Re: new lichen

PostPosted: Mon May 05, 2014 1:31 pm
by CarolJane
Thanks for that info Jerry,
I will be heading to Penn-y-Ghent I recon, if two types of stone are in the same area thats great timewise not to mention scientifically.
The project is more to get us to understand the process than being an in depth study, but I`ll be sure to report back with what I find!

Re: new lichen

PostPosted: Mon May 05, 2014 2:16 pm
by david perry
I've often wondered if any lichen experts out there have ever used them for dating walls? I gather they grow at a predictable rate which can be locally adjusted by calibration from gravestones in the same area.

Any one?

Re: new lichen

PostPosted: Thu May 08, 2014 6:38 pm
by CarolJane
I may have found the perfect location for my investigation!
These 2 walls run either side of a country lane, so they are facing the same direction and recieve the same light on either side.
They are also really different! I`m hoping this is because they are different stone....can anyone help with this?


this top wall has really rounded stone and is a bit irregular.


this second wall is very precise, straight and flat.

Or are they different because one is much older than the other?
please help, I`m loosing sleep over this, and counting sheep jumping stone walls isnt helping!


Re: new lichen

PostPosted: Thu May 08, 2014 8:11 pm
by jerryg
It is a bit difficult to tell with just those photos, could do with you standing further back and get a straight on wider shot of each wall.

Also it would be nice to know where these walls are. Luckily you are not having to find good well built walls, just any old rubbish will do.

Having said that, these are my educated guesses.

The stone in the first wall looks to me like field clearance stone. ie, roundish worn stones. The second wall looks more like quarried stone being more rectangular.

The significance of field clearance versus quarried stone reveals the ages of the wall.

When most fields were cleared of stone hundreds of years ago to make a field useful for ploughing etc the stone cleared was usually rounded and worn and to get rid of the stone it would be built into a wall.

When new walls were then needed in the enclosure years all the field stone had been used up and they would then need quarried stone.

So I would say that the wall built with the roundish boulders is older than the wall with the more regular rectangular stone.

Does the growth of the lichen reflect my thoughts?

Re: new lichen

PostPosted: Fri May 09, 2014 11:55 am
by david perry
We need someone like Sean from the North Wales branch!!

Re: new lichen

PostPosted: Sun May 11, 2014 1:52 pm
by CarolJane
thanks again Jerry
that makes complete sense, old weathered stone looking old and weathered! why didnt i see that?
i`m off in to the `field` again armed with vinegar to see if i find some reactive limestone and some unreactive gritstone.
Im on the York/Lancs boarder near Colne, I`ve checked and the geology around here has both so im guessing our walls do too!

hope i dont get arrested for being weired and throwing vinegar at walls :?

Re: new lichen

PostPosted: Sun May 11, 2014 4:15 pm
by david perry
Its difficult to date walls.

Although Jerry points out one of the walls is built from round stones, possibly field clearance which may well be an early wall, this doesn't guarantee it is. I do note it is quite straight and there are no enormous bolders in it. I've always believed that the walls built during the enclosures were mainly steraight for the simple reason it was the easiest method of dividing, measuring and surveying boundaries.

I would be very surprised though Carol if there wasn't some information on dating walls and stonework using lichens given there predictable(?) rate of growth?

Re: new lichen

PostPosted: Sun May 11, 2014 11:14 pm
by GregLee
At my place the stones seem to need at least 4 years of weathering before lichen can start to grow. I think growth patterns and species distribution would vary with the geology of the area, of course stones can be quite variable even over small distances. Tracy mentioned counting the different species, counting and identifying the different species might be interesting.

William Boyd wrote a novel in the 1980s, "An Ice-cream War". In it, a character dates hedgerows by counting the number of species of brambles. (chaos theory comes into it as well). You could do the same thing with drystone walls and lichen. Of course that was a novel so I can't vouch for the veracity of the method.


Re: new lichen

PostPosted: Mon May 12, 2014 4:52 pm
by bloop
I have been following the discussion on lichen and can add a couple of points that may be of interest.

The use of lichen growth as a means of dating structures is known as lichenometry. If you google this term you will find it is generally regarded as a method with dubious merit and dating results should not be regarded as definitive. For instance stone picked off the ground or taken from the face of a quarry and subsequently used to build a wall may have had the lichen growth present for many years prior to its use.

As Jerry pointed out earlier, the photos are of little use without context - a small area of a wall chosen at random is not representative. Photographs should show a much larger section of any wall, the location and stone type be identified (sandstone is acidic and limestone alkaline) and accordingly have differing microclimates affecting the lichen populations or species specificity. Compare drystone and mortared walls. When it rains, resident lichen are exposed to solutions with differing pH. Also the orientation of the wall should be identified. For walls which run mainly north to south, both faces will be exposed to direct sunlight at some time during the day. Only walls which run east to west have faces which are not exposed to direct sunlight and a good example as a basis for comparison would be comparing lichen growth on churches which have this alignment.

Re: new lichen

PostPosted: Mon May 12, 2014 5:41 pm
by david perry

There is a method of dating hedgerows in the UK called I think 'Cooper's Rule'. This involves taking a hundred yd section and counting all the woody species (bramble would be one) that make up the hedge. Do this for one or more 100yd sections.counting a number of 100yd sections.

Obviously the theory is that hedges accumulate species over the years. Its not exact and will vary depending on the amount of 'donor' trees/woody plants that are available to seed the hedge,local conditions and so on. I have checked this with a few local hedges which have known dates and it appears reasonably accurate here at least.