Lichens of ancient deciduous woodland

There is something compelling about native woodland where twigs, branches, and trunks are mantled with epiphytic flora. The juxtaposition of lichens, liverworts, mosses and polypody ferns creates a visual kaleidoscope of patterns and colours when walking through these unique woodlands. The complexity is not just visual but also on an ecological level where similar adjacent trees can have widely divergent epiphytic flora with one tree dominated by liverworts and mosses, whilst an adjacent tree has crustose and leafy lichens and another has mosses and leafy lichens. This apparent random distribution of species, as far as I am aware, is the exploitation by species of microhabitats determined by humidity/light levels/bark character/air pollution level etc. Whilst mosses and liverworts create their own unique primordial atmosphere in a woodland, the patina of 'hoary' lichens generates the atmosphere evocative of antiquity.

Oak woodland with a diverse assemblage of epiphytic lichens ~ Coille Dhubh,  Shieldaig Forest

Early 19th century oak plantation with a poor assemblage of epiphytic lichens ~ Nagshead Plantation, Forest of Dean.

It just so happens that some lichens are indicative of ancient old growth woodland, identified by the commendable detective work of ecological historians and a significant amount of survey work incorporating careful observations of habitats. In many areas of the British Isles, lichens of old woodland are glacially slow to colonise new woodland and this is illustrated from studies in the New Forest, where 200-300 years was sufficient time for most lichens to recolonise undisturbed woodland. Although the ancient dry bark lichen community (Lecanactidetum premneae) requires 400 years to recolonise after clear felling. The ecological impact of clear felling woodland in the 17th Century is only now being rectified.

The Revised Index of Ecological Continuity (RIEC) developed in 1976 lists 30 indicator lichens to grade the ‘ancient woodland’ interest of deciduous woodlands throughout the whole of Great Britain and Ireland :
1. Anisomeridium ranunculosporum
2. Arthonia vinosa 
3. Biatora sphaeroides (Current Taxon Name: Mycobilimbia pilularis)
4. Catinaria atropurpurea 
5. Cresponea premnea 
6. Degelia atlantica/or Degelia plumbea/or Parmeliella triptophylla 

Degelia sp. (atlantica?) and Lobaria pulmonaria on a mature Ash tree ~ Sleat, Isle of Skye

7. Dimerella lutea
8. Enterographa crassa 
9. Lecanographa lyncea 
10. Lobaria amplissima
11. Lobaria pulmonaria

Tree lungwort (Lobaria pulmonaria) ~ Coille Dhubh, NW Highhlands, Scotland

12. Lobaria scrobiculata
13. Lobaria virens

Green satin lichen (Lobaria virens) - Loch a' Mhuilinn SAC

14. Loxospora elatina
15. Nephroma laevigatum
16. Pachyphiale carneola
17. Pannaria conoplea
18. Parmotrema crinitum
19. Peltigera collina
20. Peltigera horizontalis
21. Porina leptalea
22. Punctelia reddenda
23. Pyrenula chlorospila/or Pyrenula macrospora
24. Rinodina isidioides
25. Schismatomma quercicola/or Pertusaria pupillarisv
26. Stenocybe septata
27. Sticta limbata

Sticta limbata ~ Meirionnydd Oakwoods SAC

28. Sticta fuliginosa/or Sticta sylvatica
29. Thelopsis rubella
30. Thelotrema lepadinum

A formula has been developed to rank the degree of ecological continuity of woodland from the species density of REIC lichens in a square kilometre of woodland:

• 15 or more RIEC lichens and there is "clear evidence of an ancient woodland with a long history of ecological continuity; the woodland has never been clear-felled or extensively coppiced, although trees may have been felled on a selective basis".
• 10 - 14 REIC lichens indicates there is "strong evidence of ecological continuity". 
• 6 - 9 RIEC lichens indicates there is "evidence of some degree of ecological continuity".
• 0 - 5 RIEC lichens indicates "no indication of ecological continuity; the woodland is either a plantation or has been clear felled and regenerated, or coppiced."

There are a number of caveats with the RIEC as it assumes levels of air pollution have not negatively impacted on the lichen population, was based largely on those Lobarion or Lecanactidetum communities found in the New Forest and lowland English parklands and some lichens are geographically restricted.

Screenshot of a map showing areas where each Lichen Index for Ecological Continuity for deciduous woodlands is appropriate http://www.britishlichensociety.org.uk/about-lichens/indices-ecological-continuity-woodland-epiphytic-lichen-habitats

Since 1976 further insights into lichens and their habitats has been been elucidated with indices developed to cater for regional distributions and rating the conservation value of woodland:
New Index of Ecological Continuity (NIEC)
West of Scotland Index of Ecological Continuity (WSIEC)
Eu-Oceanic Calcifuge Index of Ecological Continuity (EUOCIEC)
East of Scotland Index of Ecological Continuity (ESIEC)
West Ireland Index of Ecological Continuity (WIIEC)

Tree lungwort (Lobaria pulomaria),  Green satin lichen (Lobaria virens) and Bark barnacle lichen (Thelotrema lepadinum)  on a mature oak ~ Tower wood, Killarney National Park 

Many of my local woods in the Forest of Dean and Wye Valley are designated as ancient in origin and sadly clearly demonstrate the effects of historic air pollution AND adverse woodland management. Centred on a coalfield and downwind of the Bristol and South Wales coalfields the area has been subjected to pollution from coal burning associated sulphur dioxide emissions and 'acid' rain. The woodland management has seen extensive coppice management for charcoal and then conversion to broadleaf and evergreen plantations. The Nagshead Plantation in the Forest of Dean illustrates the slow rate of lichen recolonisation, it was clear felled and replanted with oak in the early 1800's and a Forestry Commission handbook on lichens (1989) records that the Nagshead Enclosure has no lichens indicative of old woodland and 16 other epiphytic lichens. The same handbook has a listing for old growth oak woodland with glades in the New Forest with an impressive 20 REIC lichens and 300 epiphytic lichens recorded.

Bark barnacle lichen (Thelotrema lepadinum) indicator of 'Old woodland', Speech House Oaks SSSI, Forest of Dean

Consulting the NBN Atlas indicates that the Speech House Oaks SSSI is the richest area in the Forest of Dean for REIC lichens:

• Anisomeridium ranunculosporum
• Arthonia vinosa
• Cresponea premnea
• Enterographa crassa
• Loxospora elatina
• Porina leptalea
• Schismatomma quercicola
• Stenocybe septata
• Thelotrema lepadinum

None of which are macrolichens, which means you need to get up very close with a hand lens to see any detail and then some competence to then identify them. Which is why there is only one image of the bark barnacle lichen to illustrate the Speech House Oaks SSSI REIC community. Taking an interest in the lichens at least provides an opportunity to appreciate the micro-habitats of woodland and an insight into their ecological continuity.