The Botany of Iceland - 01.12.1945, Blaðsíða 97

THE VEGETATION OF CENTRAL ICELAND
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passes into either a lichenous shrub heath or the Grimmia heath. Here
the sand-drift is much less than farther westward, and the precipitation
is much greater. Near Eyjabakker the upper limit of the shrub heath
occurs about 650 m above sea-level. In the bottom of Víðidalur, c.
400-450 m above sea-level, the shrub heath is replaced by a Salix scrub,
but on the mountain sides the Salix vegetation is almost exclusively
found in snow-patches.
The Salix heath is absent from the western part of Landmannaafrjet-
tur. It is not met with till we come east of Námakvísl, but nowhere
attains any great distribution here. The shrub heath is fairly widely
distributed near Geldingsá and Stórihvammur, and likewise along Jö-
kulsá eystri, wherever a closed vegetation is found. Shrub heath was
also found near Laugafell, at c. 720 m above sea-level. In Eyvindarver
and Illugaver it is found in the outer parts of the oases. On Síðumanna-
afrjettur the shrub heath is a sparsely developed formation, having
been replaced by the Grimmia heath. On considering the precipitation
within the different areas, I arrive at the result that the occurrence of
the shrub heath is rather definitely inversely proportional to the pre-
cipitation. Where the precipitation is low, the shrub heath is widely
distributed, whereas in areas with an abundant precipitation, as on
Síðumannaafrjettur, the shrub heath is only sparsely distributed.
The most important associations of the shrub heath are:
1. Salix glauca—Festuca rubra—Equisetum arvense-Ass.
(Tab. XIII. A-B, 1-4).
In addition to the three character species, Equisetum varieg/itum,
Juncus balticus, Polygonum viviparum, and Euphrasia latifolia are
dominants. As to the last-mentioned species it should be noted that in
spite of its fairly frequent occurrence in the shrub heath, it is nowhere