A full version of this article appears in the magazine.

 

The heart of any lichenologist cannot fail to miss a beat at the sight of any one of the four species of tree lungwort lichens Lobaria spp. that occur in Wales. They are what lapwings and corncrakes are to ornithologists or butterfly orchids to botanists. Grown well, lungwort lichens can reach the size of dinner plates and were once probably the dominant lichens on mature and veteran trees across most of Wales. As the common tree lungwort Lobaria pulmonaria in its convoluted surface looked rather like a lung, it was used to treat lung diseases.

 

Lung diseases must have been common in our ill-ventilated, smoke-filled homes. Ironic then that once we had invented the chimney the fate of tree lungwort across most of Mid Wales was sealed. It hated the sulphurous flue gasses created by burning coal and as industrialisation proceeded in the English Midlands and South Wales the sulphurous smoke spread, killing off or severely impairing the reproductive performance of these lichens in Wales.

 

They suffered in a number of ways. Close to the source of pollution the early-oxidised products of coal combustion, notably sulphur trioxide, were highly toxic. At a distance sulphur and nitrogen oxides were converted into tiny droplets of sulphuric and nitric acid. The droplets settled on trunks and branches or were washed out by snow and rain and acidified the tree bark. Unfortunately tree lungwort lichens all avoid the most acidic of bark and seem to require basic bark (more alkaline than acid) to grow well.

 

They were fortunately still able to find some basic bark in sheltered north to south running ravine woodlands where the worst of the pollution from the east blew over the top. Being long-lived species (colonies have now been observed for over 27 years on a single tree) they have also survived in a few places on veteran trees whose bark is naturally more basic than on younger trees and whose enormous overhanging branches shelter the trunks from some of the acidified rain.

 

Reproduction

The common tree lungwort reproduces in a number of ways. A single large plate-like colony can grow outwards as the centre dies to form a number of new colonies. This lichen can also form small, brittle lobes that easily break off in the wind or could be spread by animals as diverse as birds or mites. Both the alga and the fungus that make up the lichen travel together by these vegetative reproductive methods.

 

Alternatively the fungus can reproduce alone by producing spores from brown shield-shaped structures that form on the lobes. The spores must take their chance of alighting close to the right alga to reform the lichen. These fruit bodies never seem to form any more in almost all of the mid Wales populations. Specimens collected before the industrial revolution were wonderfully fertile. The reasons for this change are unknown. Existing pollution levels may be debilitating. It is more likely that populations are now so fragmented that the right mating strains never meet. Unfortunately next to nothing is known of the sexual proclivities of lichens.

 

Examples in Wales

Within Brecknock and Radnor since 1978 only 23 trees with the common tree lungwort have been found. Within the last 29 years 11 of those trees have either been felled (2), partially or completely collapsed (5) or lost their tree lungwort for known (1) or unknown reasons (3). Only twice what appears to be recent colonisation of new trees has been seen, and then only close to existing colonies. Nowhere can it be found on adjacent trees. All colonies appear now to be isolated and relict.

 

Recent work in Europe where these lichens are just as threatened has suggested that in native spruce forest, after calculating all the risk factors, only sites with more than 15 colonised trees have any long term future. Spruce probably has a similar life span to ash and whilst oak may live longer it may only be suitable for colonisation by lungwort late in life. So left to their own devices no sites in mid Wales appear to be viable for the commonest lungwort species. With just one tree supporting L. amplissima and L. virens these species have little future. The race is now on to try and identify those few sites in Wales where long term viability for lungwort seems likely and ensure their importance is recognised and to find ways of assisting their survival in other sites.

 

Fortunately it is possible to transplant lichens such as lungwort. The tiny vegetative propagules called isidia can be trapped in surgical gauze and stapled to new trees. With growth of about half a millimetre in 5 years and a tasty item in the diet of tree slugs, success by this most natural of methods is not that certain. Whole lobes can be successfully trapped against new trees using nylon net. This technique has now been employed in a few sites in Wales and recently for the first time a transplant on an ash tree in Ceredigion appears to have successfully propagated itself with new colonies being founded above and below it on the tree. This form of intervention may not suit the purists; but as it is our activities - pollution, the fragmentation of woodlands and the destruction of ancient trees - that have brought about this demise, surely it is worth this extra effort to conserve this most emblematic group of lichens?

 

Ray Woods is Plantlife’s Lower Plants champion.