The Botany of Iceland - 01.12.1930, Page 95
STUDIES ON THE VEGETATION OF ICELAND
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It is chiefly these species which cause the greater density of species
on the valley slopes.
Biological differences also occur. Thus the Ch percentage is
higher in the high than in the low mo, wheréas the reverse is the
case with the H percentage. The high E percentage of locality No. 7
is due to a deeper and more constant snow-covering in the winter.
The Mvri Vegetation. Cf. table 20 A, 1—7.
Owing to the short time at disposal only a very few of the mýri
formations were investigated; these were a series of moist formations
in the halla mýri (1—5), and a couple of formations in the fór-
mýri (6—7).
The halla mýri is only found along the foot of mountains,
and it is essential to its occurrence that the ground-water comes to
the surface. This causes a peculiar difference betM'een the halla
mýri (well mýri) and the fórmýri (swampy m\TÍ). In the fórmýri
the amount of moisture is determined by the precipitation on and
around the depressions in the mýri; the quantily of nutrition sup-
plied by the precipitation is comparatively small or nil, just as also
the temperature conditions are relatively closely dependent on the
temperature of the air. In the halla mýri tlie nutrient salts are
constantly renewed by the ground water, the temperature of whicli
will
more or less iníluence the temperature of the soil according
to its amount. The temperature of the ground water is constant
througliout the year, that is to say, it is equal to the mean annual
temperature in the locality in question. Thus the halla mjrri will
be warmer in the winter but cooler in the suminer than the swampy
myri. As a result the species group spectra differ widely. The lower
E sub-groups (E 3 and E 2) dominate in the halla mýri owing to
the favourable temperature condilions in the winter(l) and A2 and
A 3 species owing to the cool summer soil (!), while the A 1 species
ai'e peculiar to the flói of the fórmj'ri.
Owing to the larger amount of nutrition the number and density
of the species is greater in the lialla mýri than in the fórmýri,
especially in the dampest areas. The biological spectra agree in
regard to the preponderance of the geophytes, while there is an
essenlial difference in the chamaephytes, the Ch percentage being
highest in the fórmýri.
In the halla mj'ri the physiognomical dominant is Equisetum
dalustre, as in the fórmýri it is Carex Goodenoughii besides Erio-