Lichens in the Park

[Jo Corke]

Welcome to the Lichen Blog.  

The lichens in the park are doing well on trees trunks, branches, fences and even on the concrete and some of the paths.  Lichens often favour just one or two of these habitats.

The high winds (Nov 2010 and later) have allowed me  to collect lichens from fallen branches.

Here are some of the lichens we have identified.

Lichens in the Park July 2012.doc

This photo (Simon Randolph) taken Nov 2011 show the lichens covering the trunk of an Ash Tree near the depot.

We have several Ash trees Fraxinus excelsior and these species do indeed, at a casual glance seem to have more lichens on them than some other trees, for example our Pines, Pinus nigra which have relatively few lichens. 

This British Lichen Society table suggests that the acidity of the bark of the tree determines, to a large extent, the lichen species which will grow.

Bark pH                             Tree species
Low (acid bark)                Oak, Birch, Cherry, Alder, Sweet Chestnut, Rowan, Hawthorn, Hornbeam, Pine
Medium (neutral bark)      Hazel, Ash, Sycamore, Willow, Beech
High (basic bark)              Elm, Lime, Elder

Roger Deakin's 'Wildwood - A Journey through Trees' is a beautiful piece of nature/travel writing, on a par with Richard Maybey who we think is the British natural history writer who others can only aspire to. Roger has a chapter on Ash trees and at one point he 'lichens do well on ash because its bark is less acidic. They like poplar, sycamore and willow for the same reason, and thrive less well on the acid bark of trees like pine, oak, birch or alder'.

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More  information and thoughts on this subject here

There is a key to common lichens on British trees   here

[Simon Randolph]

Jo, The comment below I originally wrote to be added to your photo of Candelaria concolor (posted on Dec 17th '11) but it ( the comment) seems to have got lost somewhere and is perhaps better added here on the lichen blog anyway:

Well spotted, Jo.  The trouble with pollution is that it comes in various forms.  So, although Candelaria concolor is 'usually found in areas of low pollution', I would guess because it is a nitrophilous species, that it is quite happy in our park growing on the nitrogen-enriched bark substrate.  And where does this nitrogen come from? Urban car exhausts.  So whereas sulphur dioxide pollution has fallen considerably in recent years in city air, which was I think the main pollutant that created the acid conditions that most lichens couldn't tolerate, pollutants like nitrous oxides etc, from car exhausts have actually benefited the nitrophilous species. That's my totally unsubstatiated theory anyway!

[Jo Corke]

Good point, Simon. Ash bark is smooth grey or a pale grey-brown in young trees. In older trees

the bark becomes fissured into interwoven ridges.

This may be a good surface for colonisation.

This picture from wikipedia.

A good project, though there is probably

already some published info on this.

[Simon Randolph]

Interesting. pH clearly is a factor, probably the most important one.  But, after taking pH into consideration, I would have thought the degree of roughness/corrugation/grooving of the bark surface might also play a significant part, where smoother barks provide a less conducive surface for a lichen species to establish itself on. For example, Beech has rather smooth bark and doesn't seem to have much in the way of lichen growth.Though this is clearly not the case on the very broken and rough surface of the Pines. So the pine bark pH does seem to be the dominant factor influencing the degree to which lichens colonise it. But my guess is that there are quite a lot of other factors than just pH that influence lichen growth. A small research project here?!

[Jo Corke]

A good question.  We have several Ash trees (Fraxinus excelsior) these species do indeed, at a casual glance seem to have more lichens on them than some other trees, for example our Pines, (Pinus nigra) which have relatively few lichens. I have posted more information and thoughts on the Lichen Blog.

[Simon Randolph]

I'm hugely impressed, Jo. Thanks for the IDs. How many species have you positively identified for the park as a whole? And not so easy a question: Why do the ash trees seem to provide a particularly attractive habitat for colonisation by lichens?  Other tree species in the park don't seem to have the diversity or density of lichens that the several ash trees support.

[Jo Corke]

Hi Simon,  so here's how I spent the last couple of hours......

The easiest one to identify is the yellowish orange Xanthoria parietina.
The tiny grey whiskery lichen is Physcia tenella.
There are two flat grey lichens in the photo; the one with the squared-off lobes is Parmelia sulcata. 

The other could be either Parmelia subrudecta or Hypotrachyna revoluta – I went to the tree in question and found both. 
The moss is probably Ceratodon purpureus, which is present on this tree.

This tree is great - there are several other lichens and mosses on it - one day I might make a full list.

[Simon Randolph]

Here is a close up of the same ash tree trunk showing several lichens plus mosses.  Jo will hopefully give them a name.

[Simon Randolph]

When you say 'we', Jo, you really mean just you.  You are the only one with sufficient expertise to do this!