Lichen communities in the British Isles: A preliminary conspectus

312 P. W. James, D. L. Hawksztorth and F. Rose
Artlrcnietum impolitae treated above. It certainly occurs in Francc in tirc
F6rct de Fontainebleau and Brittany.
Leprarietum candelaris (Matt.) Barkm.
Phytos. Ecol. crypt. Ep., 355 (1958).-Lestraria candelarr-s Gesellschaft N,Iatt..
Ber. West-preuss" bot.-zool. Ver. 59, 16 (1937)"
'lhe Leprarietum candelarzl is dominant on the dry north and east sicles o1,
hardwood trees in forests in relatively unpolluted parts of the British Islcs
where the rainfall is rather low (particularly in north-east scotland near the
Moray Firth). Elsewhere in southern and eastern England it is largeh,
confined to dry bark crevices, where it is often associated with Schismatonrma
decolorans, although it does occasronally sprcad from crevices to fulh'
exposed, raised flattened bark surfaces in a few lotv-rainfall southcrn
areas (e.g. extreme south Devonshire).
The Leprarietum candelarzs is closely related to the calicietum hy'perel.li
and appears to be a more lowland countcrpart of it in the British Isles.
Leprarietum 'incanae ass. nov" prov.
l'his association has a similar ecological amplitude to the coniocybetunr
.furfuraceae occurring not only on the shadecl parts of trees but also o'
humrrs, on dry porvdery soil in rock crer.ices and on rock. Lepraria incanu
often occurs in almost purc stands l>ut cladonia coniocraea, Lecideu
granulosa and L. uliginosa frcquently cnter into the association on trees.
a'he Leprarietum incanae is the most shade and air-pollution tolerant of tht
associations of the Calicion hyperelli treated here extending far into urban
areas in cracks of the bark on the basal parts of deciduous trecs.
O p egr aphe tum fus c e ll ae Almb.
Bot. Notiser, Suppl. I (2), 140 (1948). F'uscelletmn Almb., K. sxenska Vetensh-
Akad. At:h. natursk.lf , 37 (1955).
A rather specics-poor community dominated by opegrapha xernicelliJert,
occurring mainly in woodlands on dry bark of deciduous trees but somctimes
spreading on to adjacent Hedera stems or siliceous rocks. Aclditional
important components include O. ochrctcheila, O. z;ulgata and Pyrenulu
nitida. This association occurs on a wide range of deciduous trees, al,
though also knorn'n from conifers, but in Britain prefers somewhat bascrich
barks. Interestingly, like the Parmelietum reL^olutae (see p. 331) it is
found on conifers only in areas where there is little or no air pollution
10. Lichen Communities in the British Isles 313
Two facies of this community can bc recognized in the British Isles: (1)
the typical nodum on shaded basic barks (.e.g. Lllmus) with Opegrapha
t:ernricellifera, O. ochrocheila and O. lichenoides, and (2) onc on shaded
more acid barks (e.g. Fagus) where O. niveoatra predominates and Pertusaria
leioplaca and Graphis species are characteristically present. The
Opegraphetum fuscellae, as conceived here, has a rather southern and
western distribution in the British Isles.
Lll. 2. Clq.donion coniocraeae
Cladonion coniocraeae Dr,rvign., Bull. Soc. r. bot. Belg. 74, +9 (1942); type:
C ladonietum conio cr ae ae Duvign.
This alliance was first describcd from Belgium for communities dominated
by Cladonia coniocraea and applicd to British communities by Laundon
(1956, 1958, 1967) and later authors. 'l'wo associations are recognized in
Britain both of r,vhich can occur on tree bases ancl peaty soils.
C ladonietum c enote ae F r ey
Verdff . Geobot. Inst. Rubel 4,2+9 (1927).
This association, first described from Scandinavia, is used here in its
original somewhat restricted sense (see below) for the Cladonia-rich
communities which are found on very dry and acidic tree bases, dead
stumps and on peaty soil under mature native pine woods in the Scottish
I{ighlands. It is particularly well developed in the Glen More and
Rothiemurchus Forests where it includes as its characteristic species the
rare or local C. botrytes, C. carneola, C. cenotea, C. defctrniis and C. nemoxyna
as well as the more widespread C. furcata, C. gonecha, C" gracilis, C.
scabriuscula and other moorland Cladoniae.
C ladonietum c oniocr ae ae D uvign.
Bull. Soc. r. bot. Belg.74, +9 (19+2).
\-he Cladonietum coniocraeae is a well marked community which is both
pollution tolerant in the British Isles and has a wide ecological amplitude,
occurring on the bases of shaded trees (sometimes extending far up the
trunks in ravine-like sites), rotting wood, clayey and pcaty soils, and
siliceous rocks in damp situations. The community, when optimally
developed, is rich in species of Cladonia, although C. coniocraea is the most
important; others commonly encountered include C. chlorophaea, C'
digitata, C. fmbriata, C. macilen.ta, C.'pyxidata. s. str. and C. squamosa" An