Lichen communities in the British Isles: A preliminary conspectus

308 P. W. James, D- L. Ilawkszporth and F. Rose
This association rvas described by Hilitzer (1925) for cornmunitics don.ri
natecl by calicium ztiride and in u-hich r,ecanactis altietirm was oftcn ,
major component. In the .British Isles this generally spccies-poor assr.,ciir
tion occurs on dry, rough or moderatcly smooth (e.g. Acer) bark or clrci
duous trees in lowland areas (most frequently in those subjccted to moclcral,
air pollution) and also on coniferous trees in central and castern Scotlantl
communities dominated by Lecanactis abietina appear clistinct frorn tl r
cali.cietum hy1>erelli in the British Isles and that specics is rarely a n'rajt,
componcnt of this association here. Lecanctra expallens, Lecidea scaluri
Lepraria incana., sometimes Buellia schaereri (central and eastern Scotlancl
Catillaria grffithii and schismatomma decolorans, entcr this associati.
but it most commonly consists of almost pure stands of calicium salicintrti
C. ztiride, Chaenotheca ferruginea and Le.praria candelaris. Chaerufilrct
ferruginea predorninates in polluted areas whilst Schismatomma xirghtert,
occurs in the driest facies ofthis association.
ln lovvland Britain the Calicietttm hyperelli is most commonly fountl r,
the dry (usually north-east) sides of u'ell lit deciduous trees which car.r
cither the Parmelion perlatae or Xanthorion parietinae on their better- l
and wetter sides. Allied to this association is a further casily ovcrlookt
community u'hich may be distinct, which occurs in dry sheltered bar
crevices of rather basic-barked trecs (e.g. F'raxinus, Salix, (,'lmus) particr
larly in south-east England and central Scotland. 'I'his community
dominated by Chaenotheca trichialis togethcr with C. hispidula, C. curtlt,
siae, C. laeoigata and Cont)ocyhe sulphurea.
C o ni o c y b e tum furfur ac e a e Kalb
Ber. bayer. bot. Ges. 41,70 (1969).
The Coniocybetum,furfuraceae, characterized by abundant Coniot',t'i
furfuracea, occurs in more shaded sites than the Calicietttm hltperclli al
when on trees is restricted to basal crevices, exposed roots etc. 'l'lr
association is not exclusively corticolous ancl also occurs on soft hurrr
and in rock creviccs where it is protected from direct rain. The Coniot_,
betum furfuraceae is mainly restricted to rvestern and northern parts of tl
British Isles, When on rock this association may include elements of tl
Micnreetum sylxtlcolae (p. 366) and its relationships to that comnrnnir
nrerit further study.
Lec anac tidetum abietinae Hrl.
Spisy Pfirod. Fac- Karl. Unia.4l,9+ (1925) fas "Association i. Leca.nott
a.bietina."l.
10. Lichen Communr'.ties in the llritish l.rles 309
Comrnunities dominated by Lecanactis abietina occur in gencrally sirniLrr
habitats to the Calicietum hyperelli but favour somcu'hzrt r-r-rore shadcci
and htrmid situations, for examplc dry, very acid bark of [tinus or Ouercu.r
within a wood rather than isolatecl trees in pastures. The zrssociation can
perhaps be viewed as a dry bark counterpart of the Parmelietum laeaigatae.
Where this association is optimally developed, the L. abietina rvith apothecia,
Calicium r:iride is often completely absent, ar-rd while Clmenotlteca .ferruginea
is often to be found in the vicinity, it tends to be on slightly less
sheltercd parts of the trunks and to represent a fragment of the Calicietum
hyperelli rather than forming a part of the present association. The
Lecanactidetmt abietinae is rather poor in specics in thc Ilritish Islcs
although Lepraria incana and Schismatommtt decolorans nray occur in it
from time to time. Arthonia leucopellaea, Lecana.ctis amylocea and somctimes
1,. corticola or L. d.ryophila, are rare members of this association
occurring in, for example, south-u'estern ancl north-eastcrn Scotland ancl
the Nerv Forest. In old r,r,oodland areas Schismatomma nioeum is also a
frequent member of this association.
Lecanactidetum premneae ass. nov. (Table I, F-ig. 2)
This very distinctivc association, lhc " Schisma.tontme decolorans-Lecanactis
premnea--Opegrapha lyncea community" of Rose and Jamcs (1974),
appears to ultimately become the post-clinlax commur)ity of very ancicnt
(over 300 years) Ouercu.r trees ancl can cover their entire surfaces both in
open parklands ancl in forested areas (e.g. thc Ner,v Forcst) in southcrn
Britain. It colonizcs bark surfaces which have bccome dry and brittle lvith
age and lost their water-holding capacity but retained a rclativcly high pIJ.
Though an association clearly relict from ancient forcsts, it does not nccd
a forest microclimate to survive and can occllr on ancicnt, nou' isolatccl,
trees. 'Ihe association is unknown in Scotland and appears very rarcly in
Ireland.
The characteristic species of the Lecanactidehtm ?remneae are Lecanactis
premnea, Opegral>ha lyncea, O. prosodea (extreme south of England only),
Schisnmtotnma decolorans, and sometimcs S. r:irgineum. Arthonia impolita
and Buellia canescens are sometimes present in pasture sitcs. Although
almost entirely restricted to agcd Quercus (though also known on agccl
Fagus), a facies of this association (lacking O. lyncea) occurs on extremcly
ancient Taxus trees (usually in churchyards).
This community has been littlc understood in the past, doubtless duc tcr
tlre scarcity of ancient Quercus trees outsidc the British Isles, but elemcr.rts
of it wcre includcd by Barkman (1958) in his rather broad concept of the