Lichen communities in the British Isles: A preliminary conspectus

322 P. W. James, D. L. Ilawhsworth and F. Rose
ambigua, for examplc, start to
he lower end o{ its sulphur
latter plants represent inter_
of the Psea
bark is nu
particularly by soot, Desmococcus enters into '
-rhe Lecanoretum pityreae is often tacked by Atheria arachnoidea (Berk.j
Jtil. which can form large pale lesions in it.
Lecideetum ostreatae (Hil.) comb. nov.
Psoretum ostreatae Hil., sp^y pfirott. Fac. Karr. Llnht.4l,gg (lgzs)[as .,Association
d Psora ostreata"f.-Lecidceturn ostreatae schulz 1s"n.,u-rtorth], Beih.
leddes Refert. 67, +8 (1931) las ,,Lecidea ostreata_Ass.,,j._Lecideion ortreata,
!3"".{,, in_Kettering and Disirict Field Club, First Fifty years,94 (1956) [as
"Lecidion"l.-Lecideetum scalaris Kalb, 1)zss. Bot., Lrh* g, '37 (1970) [as
"Hilitzer 7925"1.
This air pollution-tolerant association is mainly confined (in moderately
polluted areas) to the bark of deciduous trees in shelterecr, wJll lif .sites, but,
Iike the Lecanoretum pitl,reae, will also occllr on coniferous trees at rower
sulphur dioxide levels. Although an essentia
also occasionally encountered on decorticate
and tree stumps), sandstones and brick in m
British IsIes. Lecidea scalaris predominates i
times the only species present. cradonia coniocreea, c. fimbriata, Lecanore
conizaeoides and Lecidea granurosa may arso o..rrr'butlenerallf ha'e low.
cover values. 'rhe Lecideetum ostreaiae also occurs on charred trunks;
Lecidea scalaris often fruits in this habitat aod. Lecidea friesii ani Toninia
carodocensis may also be components of this speciali""j fnci...
All. 6. Loborion pulmonariae
Lobarion pulmonariae Ocl.rsn., Jahrb. St. Gall. naturw. Ges. 63, 64 (192g); type:
Lobarietum pulmonariae Hil. [syn. Nephrometum laeoigatae nr.f.rn.j. --
'lhe Lobarion pulmonariae (Fig. 3) is composed mainly of large foriose
lichcns and robust bryophytes ancr'appears io bc the ,atrr."l fore-.st climax
community on mature harirwood i.... ,uith barks of pH i.-o-o.o i,
diterranean climates. ft is nou, very
to the felling and management of
forms of pollution. In drier areas it
there is more light, or to the "on.,ofiio*i'.t:ri:::Jt3t,H:T.ix
10. Lichen Communities in the British Isles J Z.'
FIc. 3. Lobayion pulmonariae on oak. Predominant species: Lobaria amplissima.
(with cephalodia) and L. pultnonaria (Argyllshire: Ardnamurchan Peninsula,
Camasine, 1967, F. Rose).
Scotland and Brittany it is largely restricted to mature or older tree trunks
but in these two regions it wlll occur on relatively young trees and even
old Corylus bushes. In parts of Scotland with high humiditics it is even
able to colonize planted trees or avenues while elservhere it has acquired
an essentially relict status; i.e . become confined to primary rvoodland relics
with old trees. The Lobarion is rarely well developed in coppice s,oodlands
unless l)umerous old standard trees are present but persists in many sitcs in
Enp;land on sheltered ancient parkland Fraxiruts, Quercus and (Jlnrus trees.
In drier areas (e.g. Sussex, north-east England, eastern Scotland) it is
usually best developed in forest relics in sheltered humid valley floor sitcs
or on trees close to rivers in gorges.
Today the alliance is unable to spread in drier districts into rvoodlands
less than 200 years old unless these adjoin, or have adjoined, ancient
woocllands from rvhich dispersal could take place when the trees reachcd
sufficient maturity. The ability to colonize younger trecs and exist in more
shaded sites in wetter climatic zones may be due to (1) a higher annual
growth rate (longer growing season) of the macrolichens concerncd in
the constantly humid environments, and (2) photosynthcsis being able to
occur for longer periocls in moist conditions and thus compensating for
lower light intensities.