PDF - CES (IISc)

386
ECOLOGY
(4) High shingle. The term indicates shingle aggregated into banks
lying well above all except the highest tides. A large percentage of sand
may be mixed with the stones and if no humus is present and the stones of
small size, lichens may be absent altogether. Those occurring in the "loose
shingle" are saxicolous. In the "bound shingle" where there is no grass
the stones, fixed in a mixture of sand and humus, are well covered with
lichens. With the presence of grass, a thin layer of humus covers the stones
and a dense lichen vegetation is developed both of shingle and of dune
species.
(5) Low shingle. This last association lies in the hollows among plants
of Suaeda fruticosa. Stability is high and tidal immersions regular and
frequent. The dominant factor of the association is the quantity of humus
and mud deposited around and over the stones. The lichens cover almost
every available spot on the firmly embedded pebbles. The characteristic
species of such areas are Lecanora badia and L. (Placodinm) citrina which
effect the primary colonization. To these succeed Lecanora atra and Xan-
thoria parietina. In time the mud overwhelms and partly destroys the
lichens, so that the phase of luxuriant growth is only temporary.
Lecanora badia is conspicuously abundant at the sand end of this forma-
tion. Lecanora (Placodium} citrina disappears as the mud is left behind.
Collema spp. also occur frequently on the mixture of mud and sand round
the stones. Trie species on " low shingle " are those most tolerant of sub-
mersion : Verrucaria maura is confined to this area, where it is covered by
the tide several hours each day.
FORMATION
Dune
Shingle
i. Bare Sand
2. Grey Dune
ASSOCIATION
Derelict Dune
4. High Shingle I
Loose j
(Without sand
Bound
PRINCIPAL SPECIES
Cetraria aculeata f. acanthella
Cladonia furcala
Cladonia rangiferina, Peltigera rufescens
Cladonia furcata, Cl. alcicomis
Cladonia furcata, Parmeliafuliginosa
Rhizocarpon confervoides
(Lecanora atra, L. galactina
With sand -I Rhizocarpon confervoides
{Lecanora citrina
With grasses
(Physcia tenella, Lecanora citrina, Xanthoria parietina
\ Squamaria saxicola
I Parnielia saxatilis, P. fuliginosa
\ Cladonia rangiferina, Cl. furcata, Cl. pungens
\ Cetraria aculeata
Xanthoria parietina, Biatorina chalybeia, Lecanora atn
Aspiciliagibbosa,
5. Low Shingle
Buellia colludens, J'errncaria (Without grasses
microspon
Physcia tenella, Lecanora atroflava
Rhizocarpon confervoides, Lecanora citrina var. incrustan.
L. badia, L. atra, Xanthoria parietina
Verrucaria maura
McLean adds that Xanthoria parietina in its virescent form on Suaeda
fiuticosa also endures constant immersion ; Lecanora badia does not occur