The Botany of Iceland - 01.12.1930, Qupperneq 191

STUDIES ON THE VEGETATION OF ICELAND
181
The forest ground vegetation resembles the geiri vegetation
in external factors and in its main features. The density, the number
of high-arctic plants, and the quantity of Ch are less in forest ground
than in geiri, while the quantity of H is higher. The cause for this
may perhaps be found in the differing illumination and the more
constant protection from frost in the forest ground than in the geiri.
Each of the types of vegetation discussed above comprises a
great number of formations which have not, as yet, been more closely
examined.
7. Our knowledge of the quantitative distribution of the indi-
vidual types of vegetation in the various parts and altitudinal zones
of Iceland is as yet rather deficient. Of the percentage of types in
the individual altitudinal zones, the following particulars maj' be given.
I. In the lowlands, belowr the 20 p. c. Ch biochore, the 300 m
curve, the dominant features of the landscape are forest, mo (espe-
cially heather mo), jaðar, littoral meadow, ílag, mýri (fór mýri, halla
mýri, and fét mýri), flói, dý and fén, and lowland melar.
II. In the lower highland zone, 300—600 m above sea-level,
the types of vegetation are melar (highland melar), mosathembur,
m° (level and knolly), jaðar, mýri (fór mýri), ílói, dý, and geiri (in-
cluding the Salix herbacea and the Sibbaldia vegetation).
III. In the upper highland zone the vegetation is either melar
or geiri (especially Anthelia crusts).
IV. In the zone between tlie 800 and 1200 m curves, the nival
zone, a very scattered melar vegetation is recorded. The larger or
smaller accumulations of snow are another feature of the landscape.
Above the 1200 m curve, the snow line, we come to the
V. zone, the jökulls, where all higher vegetation is excluded on
account of the continuous snow-covering.
The forces that go to form the various types öf vegetation are,
111 the lowlands, especially the differences in moisture, in the high-
lands, the differences in snow-covering.
8. The investigation of the distribution of species, species-groups,
and life-forms in the formations according to increasing prevalence
°f one and the same external factor has brought to light the fol-
lowing facts.
In a given scale of one and the same external factor the indi-
vidual species attain maximum l'requency, i. e. minimum distance
hetween individuals, at some point in the scale. Passing from this
point towards either greater or less prevalence of tlie factor under