The Botany of Iceland - 01.12.1945, Blaðsíða 100

442
STEINDÓR STEINDÓRSSON
4. Salix glauca—Empetrum nigrum-Ass.
(Tab. XIV. A-B, 1-4; XV. A-B, 1-4, 6; XVI. A-B, 7).
Compared with the preceding associations this association exhibits
by far the greatest abundance and density of species. The dominant
species in the individual analyses and the number of constant species
are much more numerous than in the preceding associations, notably
the shrubs are much more conspicuous here. This association may be
regarded as the most typical of the whole shrub heath and as the as-
sociation within the formation which differs most completely from
other formations. In addition to Salix glauca, Empetrum nigmm still
dominates but furthermore the following dominants are found: Salix
herbacea, S. lanata, Equisetum asrvense, E. variegatum, Festuca rubra,
and Carex rigida; in a few localities Elyna Bellardi and Dryas octope-
talft are among the dominant species. Here we might suitably speak of
Elyna and Dryas variants and, in some places, of Cassiope hypnoides
and Loiseleuria procumbens variants, where these species are most
numerous. The association is distributed over the eastem part of Brúarö-
ræfi and on Snæfellsöræfi, and is found everywhere under similar con-
ditions, that is to say, in dry, fairly high-lying localities with a thin
snow-covering. It shuns the most sandy soils. Its surface is almost with-
out knolls, being either quite level or slightly inclined, though with
certain exceptions, which will be explained under the individual analy-
ses. Humlum (1936, p. 63) describes precisely this type of heath
and calls it specially east-Icelandic. I hesitate to adopt this assumption
without reservation, but my observations certainly point in the direc-
tion that this association is, at any rate, far commoner in eastern Ice-
land than in the remaining parts of the country. I greatly doubt whether
it is found at all within those parts of the palagonite formation which
are most severely ravaged by blown sand, but I have been unable to
acquire information about the vegetation farther westward.
Of the formations described from other northern countries it seems
to me that this formation is most closely related to the East-Greenland
Empetreto-Vaccinietum mentioned by B ö c h e r, though there Vaccinium
uliginosum is more abundant than here. Still this species occurs so fre-
quently in the present association that it must be said to be constant to it.
Böcher (1933, p. 56 ff.) says that the Empetreto-Vaccinietum is found
where the soil is relatively damp and on south-facing slopes, in other
words, under similar conditions as the brekkur formation described
by me, which is much more exacting as regards heat and snow-cover-