Current status
This crustose lichen grows on the trunks of mature trees with basic bark. In Britain, it is largely confined to elm, but also occasionally occurs on ash, beech, holly, hornbeam and sycamore. It is typically found in old parkland and on wayside trees in open situations, usually growing as uneven vertical streaks along nutrient-rich rain-seepage tracks or below wounds in the bark. It also sometimes occurs on the exposed roots of elm on cliff faces.
Once relatively widespread throughout the British Isles,
Bacidia incompta had a scattered distribution extending northwards to Aberdeenshire, but was most frequent in southern England. In 1960 it was known from 142 sites, but many of these are believed to have been lost. A survey of some of the southern English sites show that it has become extinct in at least 30 sites. However, it has survived in some localities such as the New Forest, where it is estimated to occur in approximately 10 woods, and one site at Ashburnham Park in East Sussex, where it occurs on hornbeam. In Scotland it is still thought to exist where there are pockets of surviving elm trees, whilst in Wales, a single population was recorded in Powys in 1995, on the fragments of bark of a dead elm tree. A recent survey of the Glamorgan sites in 1997 failed to detect this species. The present distribution of
B. incompta in Britain (like that of
Caloplaca luteoalba) following the loss of mature elms is not well known; it may be a somewhat under-recorded species.
A similar decline has occurred in the Irish Republic where this species is now rare, being known only from the south and west. Elsewhere, this species occurs in continental Europe, Madeira and North America.
This species is classified as Vulnerable in Great Britain. It receives general protection under the Wildlife and Countryside Act 1981.
Current factors causing loss or decline
Since 1960 this species has suffered a catastrophic decline as a result of Dutch elm disease. Dutch elm disease remains a threat to the survival of this lichen.
Clearance and non-replacement of wayside and parkland trees is believed to have contributed to the loss of this species from a large number of sites since 1960. Further clearance and non-replacement of such trees or windblow of host trees is a continuing threat.
Drift of agricultural chemicals, including fertilisers, slurry and pesticides may be a significant threat where wayside trees adjoin cultivated land.
Current action
New pollards are being cut in the New Forest in order to help provide a continuity of veteran trees for threatened species which depend on this habitat, including specialist invertebrates and lichens such as B. incompta.
Action plan objectives and targets
Maintain populations at all extant sites.
Encourage the spread of this species by maintaining or establishing suitable habitat in the vicinity of all extant sites.
Proposed actions with lead agencies
Policy and legislation
Consider Bacidia incompta for inclusion on Schedule 8 of the Wildlife and Countryside Act 1981 if its status is confirmed as Vulnerable, if it meets relevant criteria, and if legal protection will address the causes of its decline. (ACTION: DETR, JNCC)
Site safeguard and management
Consider notifying as SSSIs sites with viable populations of Bacidia incompta where this is consistent with selection guidelines, and where it is necessary to ensure their long term protection and appropriate management. (ACTION: CCW, NE, SNH)
Where it is in the interests of amenity, apply Tree Preservation Orders to protect host trees and woodlands. (ACTION: LAs)
Wherever possible, establish sympathetic management at sites with populations of this species. Particular emphasis should be given to the protection of host trees and potential host trees, and also to preventing felling of other trees which may influence the micro-habitat of this species. Measures should be adequate to ensure the protection of host trees during road-widening schemes. (ACTION: CCW, NE, FE, Highways Agency, LAs, SNH)
Where appropriate, undertake planting of replacement host trees, including disease resistant strains of elm, in the vicinity of extant sites for this species. Assess the need for this work at the Powys site if the population there is confirmed as extant. Suitable mechanisms may include the Countryside Stewardship Scheme and the Woodland Improvement Grant Scheme. (ACTION: CCW, NE, FE, LAs, MAFF, SNH, SOAEFD, WOAD)
Assess the threat to extant populations from the drift of agricultural chemicals. Where such a threat exists, consider providing mechanisms (eg management agreements on SSSIs or relevant agri-environment schemes on land outside these areas) to address these problems. (ACTION: CCW, NE, MAFF, SNH, SOAEFD, WOAD)
Species management and protection
Consider creating artificial wounds on trees so as to provide further suitable habitat for this species and allow for the spread of existing colonies. (ACTION: CCW, NE, FE, SNH)
Advisory
Advise landowners and managers, and relevant agencies, of the presence and importance of Bacidia incompta, specific management for its conservation, and any potentially damaging actions. Landowners and managers should have access to specialist advice if needed. (ACTION: CCW, NE, SNH)
Future Research and Monitoring
Compile information and resurvey sites where necessary in order to determine the current status of this species at all sites from which it has been recorded, and to assess current threats to all extant colonies. (ACTION: CCW, NE, SNH)
Undertake regular monitoring at all extant sites to assess population changes and to ensure prompt identification of any new threats. (ACTION: CCW, NE, JNCC, SNH)
Compile a list of sites that would be worth searching for this species and distribute to active lichenologists. Particular note should be taken of old records where the tree is not elm. (ACTION: CCW, NE, JNCC, SNH)
Communications and Publicity
Raise awareness of the importance of managed parkland as a lichen habitat amongst relevant park authorities and managers. (ACTION: CCW, NE, SNH)
Encourage lichenologists to pass all records of Bacidia incompta, including ecological information, to a national database. (ACTION: CCW, NE, JNCC, SNH)
Liaise with specialist societies to increase the awareness and identification skills of lichenologists and other naturalists in relation to this species, through publishing articles or holding identification workshops. (ACTION: CCW, NE, JNCC, SNH)
Links with other action plans
None given.
Publication details
Originally published in: UK Biodiversity Group Tranche 2 Action Plans - Volume III: Plants and fungi (February 1999, Tranche 2, Vol III, p73)
Related links
ARKive Visit the ARKive website to view images and further information relating to this species