The Botany of Iceland - 01.12.1930, Side 61

STUDIES ON THE VEGETATION OF ICELAND
51
1—5 show what species are characteristic of the mo, and the F,-
percentage of the individual species. Passing from the mo to one
°f the vegetation types previousty mentioned, a transition zone will
often be met with in which the frequencies of the species have
undergone great changes. In table 11, 5, 6, and 7 show such
transition zones passing into geiri, mosathembur, and jaðar respec-
tively. A comparison of these zones, on the one hand with the
mo vegetation, on the other with the respective types of vegetation,
will show that statistically, biologically and íloristically, the zones
occupy this intermediate position.
No. 5 shows the transition from mo to geiri. The geiri plants
Vaccinium uliginosum, Luzula multiflora, and Anthoxanthum odoratum
sliow a comparatively high F.-percentage, while a mo plant Elgna
Eeltardi is inconspicuous. The proportion of A and E species points
m the same direction. No. 6 is a transitional form between mo-
sathembur and mo. A number of species whicli occur commonly
m the mo, only appear sporadically here: this is the case with
Leschampsia ftexuosa, Galium boreale, Selaginella selaginoides, Thymus
serpyllum, and Trisetum spicalnm. The density of the species is ap-
preciably diminished, being 8.6, and the character of tlie environment
more arctic. The G percentage is comparatively liigh.
No. 7 is the moist mo which forms the transition to the jaðar
vegetation. Most ol' the plants of the mo recur with the same F,-
percentage, a number of jaðar plants such as Deschampsia cœspitosa,
Luzula multiflora, Satix phylicifolia, Viola patustris, Cardamine pra-
tensis, and Taraxacum officinale begin to thrive better.
Nos. 8—9 are typical mo at a somewhat higher level, viz. 300—
400 m above sea level. The vegetation has assumed a more arctic
character. Satix herbacea is beginning to predominate in the phy-
siognomy of the vegetation.
As previously indicated, the mo is the most widely distributed
4rPe of vegetation in the Icelandic lowland where it probably com-
pnses a fairly large number of formations. It must be left to future
Plant geograpliers to classify and characterise these formations with
regard to environment, biology, and tlora, and to correlate them.
The Jaðar Vegetation.
Between the mo, whose degree of moisture is exclusively de-
termined by the precipitation, and the mýri, whose degree of moisture
determined, in addition, by the ground water, there occurs a belt
4*