PDF - CES (IISc)

LICHEN COMMUNITIES: 385
grass that lichens begin to develop, though in the cool damp weather of
autumn and winter, as observed by Wheldon and Wilson 1
certain ,
species
associated with Myxophyceae, such as Collemaceae, may make their appearance,
among others Leptogium scotinum, Collemodium turgidum and Collcma
ceranoides. Watson 2 makes the same observation in his study of sand-dunes.
When the loose sand on the dunes of South Lancashire becomes cemented
by algae and mosses several rare Lecideae are to be found on the decaying
vegetation, and with further accumulation of humus Cladoniae appear and
spread rapidly along with several species of Peltigera and the ubiquitous Parmelia
physodes. The latter starts on dead twigs of Salix repens and spreads
on to the surrounding soil where it forms patches some inches in diameter.
The association also includes Lecidea uliginosa and Bilimbia sphacroides.
On the more inland portions of the dunes numerous rather poorly de-
veloped Cladoniae and Cetraria aculeata were associated, while on the sides
of "slacks" or "dune-pans" Colleina pulposum, Cladonia sylvatica and several
crustaceous lichens covered the soil. The wetter parts of the dunes were
not found to be favourable to lichen growth.
Sandstede 3 found on the sandy shores of Riigen, from the shore upwards:
first a stretch of bare sand, then a few dune grasses with scattered scraps
of Cladoniae, Peltigerae and Cetraria aculeata. Next in order sandbanks
with Parmelia physodes, Cladonia sylvatica, Cl. alcicornis and Stereocanlon
pascliale. All these are species that occur on similar shores in the British
Islands. Sandstede adds an extensive list of maritime species observed by
him in Riigen.
A very careful tabulation of lichens at Blakeney Point in Norfolk was
made 'by McLean 4 and the table on p. 386 is reproduced from his paper.
Sand, he writes, is present in all the associations and the presence or
absence of stones marks the great difference between the two formations
determined by dune and shingle.
(1) Bare sand, which is the first association listed, is an area practically
the few lichen plants, Cladonia furcata and Cetraria
without phanerogams ;
aculeata f. acanthella, are attached by slight embedding
in the soil.
(2) Grey dune. The sand-loving lichens of the associatipn grow in
company with Hypnnm cupressiforme and attain their greatest development.
Other species which also occur there are Parmelia physodes and Evertiia
prunastri var. stictocera.
(3) Derelict dune. This part of the dune formation occurs here and
there on the seaward margin where the grey dune has been worn down by
the wind. It is more shingly, hence the presence of stone lichens; dune
phanerogams are interspersed and with them a few fruticose lichens, such as
Cladonia furcata.
1 Wheldon and Wilson 1915.
S. L.
- Watson 1918'.
3 Sandstede 1904.
* McLean 1915.
2 5