skipper's island papers 331
The following observations on the lichen flora have been
carried out as part of an ecological survey led by Mr. E. F.
Williams and actively supported by various other members of the
Field Club. I am much indebted to Mr. Williams for his generous
hospitality and co-operation during my visits to the island.
The island provides four main kinds of habitats for lichens,
viz.:—(1) soil; (2) bark of trees and shrubs; (3) wood; (4) bricks.
The flora of each is very distinct and will be described separately.
1. Soil. Only on the sea-walls is the vascular plant vegeta-
tion sufficiently open for the growth of terricolous lichens. The
sea-walls themselves are mostly covered by dense grass, chiefly
Agropyron pungens, but along the south shore, this is in places
rather sparse, and there is a fairly rich grass-heath type of lichen
association in which Cladonia rangiformis is the most conspicuous
and abundant species. The following species have been
recorded: —
Lecanora dispersa (Pers.) Rohl. r
Biatora uliginosa (Shrad.) Fr. o
Cladonia pyxidata (L.) Hoffm. o
C. chlorophaea (Flk.) Spreng. o
C. fimbriata. (L.) Fr. r
C. conista (Ach.) Robbins ex Allen r
C. coniocraea (Flk.) Spreng. o
C. cornutoradiata (Coem.) Sands. o
C. pityrea (Flk.) Fr. r
C. cervicornis (Ach.) Schaer. 1 a
C. furcata. (Huds.) Schrad. f
C. rangiformis Hoffm. a
C. macilenta. Hoffm. f
Peltigera polydactyla (Neck.) Hoffm. r
(a = abundant, la = locally abundant, f = frequent, o = occasional;
r=rare)
Cladonia rangiformis grows to a certain extent amongst
Agropyron, although never where this is thickest. In places,
however, chiefly on the top of the sea-wall rather than on the
sides, Agropyron is sometimes absent, and the chief flowering
plant is Plantago coronopus; here C. rangiformis may sometimes
be the dominant species, but is often scarce or even absent, its
place being taken by C. furcata (together with species of the
pyxidata-fimbriata group) and in one place by C. cervicornis.
These open patches have been found to have a somewhat lower
pH than the areas covered by Agropyron. Six soil samples taken
from 0"-2" from each of these two kinds of communities had
the following pH values (determined by a Lovibond Compara-
tor) : —
Agropyron dominated areas: 5.2. 5.4, 5.4, 5.6, 5.6, 5.4.
Plantago-lichen patches: 4.6, 4.8, 4.6, 4.4, 5.0, 4.6.
Although there is considerable evidence that the pH of the
substratum is an important factor in the ecology of lichens, the