Lichen communities in the British Isles: A preliminary conspectus

352
a site, (2) successional and competition effects
, (3) the softness (e.g. the calcium-silica ratio)
(4) the chemrcal composition of the rock (e.g.
The associations accepted within this alliance here all occupy distinctive
microhabitats (Fig. 7) as well as having characteristic floristic compositions
Coloplocc I um hcppionoe
Plocynlhielum nigil
Dtnnelum slenhommonoe
Gyoleclelum jenensts
Woler tempororily presenl
Phtscielum
coestoe
Le np ho lem m o bol ryos un - nodum
Leproplacelum chrysodelae
Gyaleclelum jenensis
Frc. 7. Diagrammatic section through a limestone bluff to illustrate the microhabitats
occupied by the principal lichen communities on limestone.
10. Lichen Communities in the British Isles 353
studies rrray be able to justify a larger number of associations than is
accepted here'
The correct nomenclature of this alliance, like that of two of the marn
associations treated below, is not entirely clear at the present time' For
this reason no attempt has been made to typify the names in the rank of
alliance cited as synonyms above.
C aloplacetum hePPianae DR.
Soensk. ocixtsociol. Stiltsk. Hantll. 2, +7 (1925) las "Caloplaca heppiana-Ass."l.
,,Syn Klem.
"(Ku
Klem';
'(DR.)"
"(Gu
oaria
Massd ; Lecanor etum dispersae Beschel.
rts.; ?
This association, which further study may show does indeed merit
generally present in such reduced communities. Many lichens which occur
in this association are, however, small and easily overlooked (particularly
the pyrenocarpous species; see Table VIII).
In particularly high-rainfall areas with low sunshine, especially on
* The nomenclature of this and the Placynthietum nigri (p. 357) remain confused
and require a very detailed investigation, particularly in view of numerous nonlatinized
names in the literature (e.g. Kaiser, 1926). Rather than tal