The Botany of Iceland - 01.12.1930, Blaðsíða 64

54
H. M0LHOLM HANSEN
vegetation, was met with. It is possible to distinguish between two
formations, a Salix lanata formation on the freshly formed soil,
and a Deschampsia cœspitosa formation on somewhat older soil. In
table 12, 1—6 show the composition of the vegelation in the two
formations.
Nos. 1—2 represent the Salix lanata valllendi. The soil is
only covered with vegetation in patches, the bed of the streain
spreading like a net over the surface from the top of the cone, the
meshes being íilled in with the patches of vegetation. The vegetation
is remarkable by the fact that chamaephytes are comparatively do-
minant physiognomically, especially the two Salix species, Salix
lanata and S. phyticifolia; other Ch occur more sparingly, thus Vac-
cinium uliginosum, Salix herhacea, S. glauca and Empetrum nigrum.
Of other plants grasses predominate, especially Deschampsia cœspitosa,
Agrostis canina, and Festuca ruhra, in less degree Festuca ovina
and Agrostis tenuis. Of other species of more or less importance
we may mention Pohjgonum viviparum, Equisetum pratense, Galium
boreale, Viota patustris, and Carex rigida.
Nos. 3—6 represent the Deschampsia cæspitosa valllendi.
This formation is always found where the two forinations occur
together, behind the Salix valllendi. The deposition of material has
practically ceased here, no bare patches of sand are ever found, and
the soil is covered by a dense vegetation of mosses.
The vegetation consists of a luxuriant carpet ofhemicryptophytes,
principally grasses. Physiognomically Deschampsia cœspitosa is the
dominant species; in addition Agrostis tenuis, Festuca rubra, Des-
champsia flexuosa, Carex rigida, and Agrostis canina are abundantly
represented. Some herbaceous plants occur in the grassy carpet,
thus Galium boreate, and Viola palustris, and less abundantly Equi-
setum pratense, Potygomim viviparum, and Gatium verum.
The two formations occur with the same density of species, c. 7,
and from a biological point of view they are remarkable by their large
number of southern plants. An essential diíference between them is
the Ch content. Possibly tliis dilference is due to cultural influences
such as grazing or haying.
The Mjri Vegetation, the mýri jaðar and the flói vegetation.
From considerations of space and owing to the close agreement
between these types in Lýngdalur and at Björk, lliey will be treated
later when the vegetation at Björk is dealt with.