Flóra: tímarit um íslenzka grasafræði - 01.06.1968, Side 48

Fig. 1. Section in lorvland heath soutli of Húsavik close to the sea. D. O.: Dryas
octopetala conccntrations. Note the steeper slopes of the Vaccinium snoxv dale.
it is just a statical condition or a fluctuation of breaking up, becoming
closed again, etc., while tlie hummock increases in size. In such a little
muddy place one always comes, across Pinguicula vulgaris, and I noti-
ced several similar places partly overgrown again by Rhacomitrium and
in heath vevetation, at higher altitude (100—300 m), by Rhacomitrium
and Loiseleuria procumbens. In other places one can find a scattered
pattern of young Empetrum, Polygonum viviparum and others in a
Rhacomitrium cover and then the cyclus may be complete, but if it is
a true picture I cannot say yet with certainty. That in general the exi-
stence of hummocks is a matter of moisture becomes clear when one
sees flat heath in places with good drainage. I noticed for example in
Fljótsheiði in the middle of a hummock-heath some flat stretches be-
tween two brooks; also the coastal strip of the heath between Húsavík
and Laxamýri is flat, where more inland liummocks occur. (fig. 2)
A somewhat similar situation seems to prevail in the transitions
from heath to melar (gravelly patches), although I have the impression
that it is much more a demolition leading to melar than an upbuilding
of heath vegetation. The borders are mostly rather sharp. Only in very
few places I saw shelving borders with young Empetrum and a lot of
Festuca rubra.
In the broken heath and lieath/melar transitions there is always
much Dryas octopetala. (Steindór Steindórsson.) (fig. 1) Under these
eroding circumstances the species can maintain itself longer than other
Iieath species, possibly by means of its firmer root. Towards the bor-
der of a gravelly patcli can be seen a gradually increasing of Dryas octo-
petala cover. Broken heath is everywhere in Iceland ancl this may be
the reason also why D. octopetala is a very common plant there, unlike,
for example, in Norway and Sweden.
4G Flóra - tímarit um íslenzka grasafræði