Rit (Vísindafélag Íslendinga) - 01.06.1975, Blaðsíða 147

the result. of solifluction, when the soil succmnhs to its own weight.
If the jaðar is formed in this way it is clearly distinct from the
tnire, in which case the mire may resemble a snow patch formation
uext to the moundridge, at least in highland regions. More com-
monly, however, the jaðar is as follows. The mire tract nearest
to the dry ground has coarser mounds than the mire proper and
is always drier. This results in rather special humidity conditions,
since the jaðar is drier than the mire, hut damper than the heath
or grassfield, owing to variations in the ground water level in rela-
tion to the surface. Consequently there appears a characteristic
type of jaðar vegetation, by the merging of wet ground and dry
ground species. There are also a few species which seem to thrive
hest at the humidity level of the jaðar and prefer this to any other
environment, at least they occur more extensively in the jaðar than
anywhere else. The jaðar soil is invariably moist, but the ground
water rarely reaches up into the grass roots. In spring, however,
water may linger in depressions, if the jaðar has coarse mounds,
hut the jaðar mound formations vary greatly in coarseness. Tliey
are, however, always coarser than mounds occurring in mires. Al-
though the jaðar, as mentioned before, usually occurs at the horder
°f dry and wet ground the same vegetation conditions may arise
elsewhere, e.g. on moundridges, (hró or hróf) or elevated strips in
mire tracts or in depressions in heaths which are too dry to be con-
verted into mires. Both these types of jaðar formation may become
fairly extensive. Furthermore, large alluvial formations may occur,
covered with jaðar vegetation, and it is a moot point whether plant
communities on river banlcs should not often be classified as jaðar
vegetation.
The jaðar is rarely if ever a stable vegetation type by virtue of
Bs position and topography. The slightest alterations of the ground
water level may transform its vegetation either into mire or dry
ground vegetation. In my paper 1945 p. 405 I have described a
jaðar formation at Arnardalur in Brúaröræfi “which is being con-
verted from mýri or flói into heath. Large sanddrift areas are found
ln fhe immediate neighbourhood of the valley, whence blown sand
ls constantly carried across the valley, in this way the mýri is gra-
dually filled up, but at the same time the vegetation begins to
change. The driest parts are transformed into jaðar, which gradual-
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