A Review of the Likely Impact of Chalara (Ash Dieback Disease) on Lichens that Live on Ash in VC42 Breconshire and VC 43 Radnorshire.
27 November 2012
All the evidence from the near continent, where this fungus disease has been present for several years, is that a very high proportion of trees are likely to become infected and an unknown number will subsequently die. Other forms of wildlife depend to a lesser or greater extent on ash trees. This review seeks to identify the likely worst case impact on lichens that live on the trunks and branches of ash trees in Breconshire.
An earlier pandemic of the Dutch Elm Disease fungus killed almost all the large elm trees in England and Wales. Unfortunately its full effects were never recorded in Breconshire and Radnorshire as we had a very imperfect knowledge of the lichen species that large elm trees supported prior to their death. The subsequent thirty or more years survey have demonstrated that at least five species of lichen that were recorded on elm became extinct in Breconshire and three in Radnorshire , whilst two species suffered a decline of over 50% in the size of their populations and have not yet recovered in Breconshire and five in Radnorshire.
Elm trees have a naturally very base-rich bark only approached in our native tree species by field maple, some willows and very ancient oak trees. Ash trees too have a base-rich bark, enhanced as they age. Many lichen species demand a base-rich bark on which to establish and grow. All too easily overlooked is the continued impact of acidic atmospheric pollutants that acidify the rain and then tree bark, particularly in the high rainfall areas of upland Breconshire. Ash in these areas may now be the most notable native tree able to support base-demanding tree lichens. Without ash only the non-native sycamore and Norway maple can offer some lichen species a possible refuge.
Results of the Review
Out of a total of 732 species of lichens recorded from Breconshire at least 148 (20%) have been recorded from ash. Eight species have only in the last 25 years been recorded on ash and may be dependent on ash and a further ten rely heavily on ash, with 50% or more of their population confined to this tree. Out of a total of 615 species of lichens recorded from Radnorshire at least 124 (20%) have been recorded from ash. Six species have only in the last 25 years been recorded on ash and may be dependent on ash and a further seven rely heavily on ash, with 50% or more of their population confined to this tree.
Lichens only recorded on ash in Breconshire
(Welsh conservation evaluations are given in brackets)
Agonimia allobata (NT), Chaenotheca brachypoda (VU), Nephroma parile*(NT), Normandina acroglypta (VU), Peltigera collina*(NT), Physconia distorta*, P. perisidiosa*(NT), and Piccolia ochrophora.
Lichens with 50% or more of their population confined to ash in Breconshire
Acrocordia gemmata (NT) On 3 old ash, 2 old oak and formerly on 3 elms.
Bacidia arceutina On 3 ash and one population on moss-covered rock.
Bacidia circumspecta (VU) On 1 ash and 2 oak.
Caloplaca cerina On 1 ash, and one ?hazel. Lost from one wych elm.
Gyalecta truncigena On 6 ash, 5 oaks and formerly on 6 elms.
Leptogium subtile* On 3 ash, 1 sycamore and formerly on 2 elms.
Pannaria conoplea* (NT) On 8 ash trees and 5 oaks.
Parmeliella triptophylla (NT) On 14 ash, 11 oak, 1 willow and 2 sites on rock.
Parmotrema arnoldii* (DD) On 1 ash and 1 rusty willow.
Pyrenula chlorospila On 5 ash and 1 hazel.
Other Notable Species occurring on Ash in Breconshire
The following members of the Lobarion (a Sect 42 community in Wales) occur on ash in Breconshire:- Catinaria atropurpurea (NT), Dimerella lutea (NT), Leptogium teretiusculum*, Lobaria pulmonaria* (VU), Peltigera horizontalis*, Pertusaria hemisphaerica and Thelotrema lepadinum (NT). Whilst ash is of somewhat lesser importance than oak for these species the whole community is significantly threatened in Wales and the loss of any additional sites is a source of grave concern.
Lichens only recorded on ash in Radnorshire
(Welsh conservation evaluations are given in brackets)
Caloplaca cerina, Gyalecta flotowii (Section 42), Mycoblastis caesius, Opegrapha rufescens, Parmeliella parvula* (NT), Punctelia reddenda* (NT).
Lichens with 50% or more of their population confined to ash in Radnorshire
Dimerella piniti, Loxospora elatina, Nephroma laevigatum* (NT), Melanohalea exasperata*, Parmeliella triptophylla (NT), Pyrenula chlorospila , Strangospora ochrophora.
Other Notable Species occurring on Ash in Radnorshire
The following members of the Lobarion (a Sect 42 community in Wales) occur on ash in Radnorshire:- Catinaria atropurpurea (NT), Dimerella lutea (NT), Leptogium teretiusculum*, Lobaria pulmonaria* (VU), Mycobilimbia pilularis (NT), Nephroma parile (NT), Peltigera horizontalis*, Pertusaria hemisphaerica and Thelotrema lepadinum (NT). Whilst ash is of somewhat lesser importance than oak for some of these species, the whole community is significantly threatened in Wales and the loss of any additional sites is a source of grave concern.
Other Section 42 species noted on ash include the Section 42 and national BAP species Anaptychia ciliaris. Once known from 4 ash trees in Radnorshire, one was felled, one collapsed and the lichen disappeared from a third. Its largest population occurs on its only remaining ash. It is found in the vice-county also on two sycamores, one field maple and on one fence post.
The woodlands of Wales have become fragmented and have lost most of their ancient trees with base-rich bark that provided a habitat for many lichens. Atmospheric pollutants and now, in particular acid rain has further reduced available habit. The fertility of many lichens and the availability of suitable trees in close enough proximity has also diminished to the extent where it is believed many relict populations may no longer be capable of self-replication. Small stochastic events such as the death of even a single tree many now imperil their survival.
Even before the threat posed by Chalara a modest experimental programme had been begun by the author and others to try and establish new colonies of Lobarion lichen species by the translocation of doomed existing colonies. This had met with sufficient success to convince the author that the programme should now be expanded even before the new threat to ash had emerged. The species marked with an * above are foliicolous species and have the capacity to be translocated. Others that occur on moss may also be translocateable.
An urgent meeting of Welsh lichenologists and representatives of the voluntary and agency conservationists should be called to determine desirable action and if necessary agree a protocol and prioritize actions.