Lichen communities in the British Isles: A preliminary conspectus

30+ P. W. ./ames, l). L. Hawksworth and tr'. Rose
discovcry of one or t\\'o spccies either characteristic of or faithful to a
particular community (e.g. the Lobarion) it is u'ell worth spending further
time searching for additional members of that community. A knorvledge ol,
the composition of the various communities described here is consequently
an aid to the making of comprehensive surveys of the specics
present in a particular site.
III. Epiphytic Cornrnunities
The very large number of factors determining the development of particular
corticolous and lignicolous assemblages of lichens have been tht'
subject of detailed reviews by Barkman (1958) and Brodo (1974) whost
works should be consulted for further information on these aspects
Amongst the more important of thcse in the British Isles are: (1) degrct
of illumination; (2) humidity of the environment; (3) age of the barli
surfacc; (4) degree of corrugation of the bark; (5) degree and rate o1
sloughing of bark; (6) continuity and age of woodland cover in a particular
site; (7) inclination of surfaces; (B) aspect; (9) degree of bark leaching br
rain; (10) degree of impregnation of bark with organic nutrients; (11) air
pollution; (12) pollution by agricultural chemicals; (13) pH of the barl
surface; (14) basic nutrient status of bark; (15) presence of tannins
betulin or resins etc., and (16) moisture-retaining and absorbing propertic,
of the bark.
As corticolous comrnunities occur on a living substrate they are par.
ticularly fluid and this dimension has to be borne in mind in their delimitation
as transitions between noda will inevitably be of frequent recurrencc
'Jihe epiphytic lichen communities of the British Isles are arranged herc
in cleven alliances. These are treated alphabetically, as are the associations
within thcm, for ease of reference. The main relationships of the alliances
to each other are summarized in Fig. 1 and the following key illustrates
the main floristic differcnces between them.
1. Old forest indicator species (see 'lable II; e.g. Lobaria spp '
l{ephroma spp., Pachyphiale cornea, Pannaria spp., Parmelielltt
spp., Slecla spp. and Thelotrema lepadinum) frequent to abunclant
old forest indicator ;p;i". ;;;"; ::':i': i:^'."':'::': t.'O,
2. Crustosclichensdominant .........1
Iioliose and/orfruticose lichens dominant . '. ' '... (
3. Arthoniales, stalked Caliciales, Hysteriales (including Lecanacticiaceac),
Lepra.ria spp., or pyrenocarpous lichens dominant...... 4
I,ecanoralesorCltpheliumdominant ......5
+.
-5.
6.
7.
8.
9.
10.
10. Lichen Communities in the British. Isle.s
Arthonioid, lirelliform or pyrenocarpous lichens dominant; cornmunities
of young twigs or smooth bark often in somcwhat
shaded situations . . . . Graphiclion sa,iptae (p. 31a).
Caliciales, Lecanactidaceae, Arthonia impolita or Lepraria spp.
dominant; communities of dry bark, bark recesses, or quickly
drying lignum . . Calicion hyperelli (p. 306).
Lecanora cltlat,otera, L. confusa, L. pallida, Lecidea symmi.cta or
Lecidella ela.eochroma abundant; pioneer communities of tu'igs
forming mosaics of small juxtaposed thalli
. . Lecanorion subfuscae (p. 318).
Bacidia clt.lorococca, Cyphelium inquinans, Lecan.ora cottizaeoides,
L. z;aria or Lecidea scalaris abundant to dominant; communities
not confined to twigs, often in moderatcly polluted areas, often
rorming extensive
:::: ':Ti: .^".0 :*":!,il:;:o;-'ili,,,(p. 31e)
Acrocordia, Anaptychia, Buellia, CaLoplaca, Gyalectina, Physcia,
Physciopsis, Physconia, Teloschtlstes or Xanthon.zz species, or
Parmelia acetabulum, P. elegantula, P. laciniatula or P. quercina
frequent to dominant; communities of nutrient-rich or nutrientenriched
barks in well lit situations . . Xanthorion parietinae
(P.3+2)-
Above genera and specics rare or absent; communities of mainly
nutrient-poor barks ... .. . 7
Cladonia species dominant; on bark in humicl situations, rotting
wood, stumps ancl tree bases . ... Cladonion coniocraeae (p. 313).
Cladonia species not dominant; communities mainly of well lit
sites.. ......8
Ramalina an d/or (t snea species dominant . . LJ sneion ltat b atae (p. 3 3 8).
Alectctria, Bryoria, Cetraria, Hypogymnia, Parmelia, Parmeliopsis,
Platismatia or Pseudeteraia species dominant . . . . 9
Parmelia caperata, P. perlata, P. reticulata, P. reaoluta or P. soredians
present to dominant or co-dominant; communities of well lit
moderately acid barks becoming rare in northern Endland and
Scotland Pat melion perlatae (p. 33U).
Alectoria, Bryoria, Cetraria, Paymelia laexigata, P" taylorensis,
Parmeliopsis, Platismatia or Pseudexerzra species dominant . . . . 10
Parmelia laez;igata, and/or P. taylorensis present; Cetreh)a, Menegazzia,
Mycoblastus, Ochrolechia or Sphaerophorus species often
present to abundant; communities of well lit extremely acid
ieached bark in areas of exceptionally high rainfall . . Parmel,ion
laeaigatae (p. 327).
305