Rit (Vísindafélag Íslendinga) - 01.06.1975, Qupperneq 143

The development of the flæðimýri (alluvial mire)
At Hvítárvatn it is particularly easy to see how a series of socia-
tions has created a new continuous vegetation type. A glacial river,
Fúlakvísl, flows into the lake and has gradually filled a very ex-
tensive area with deposit, Hvítámes, which is now mostly an E.
angustifolium flói, with small patches of C. Lyngbyei flói which
would perhaps be more correctly referred to as flæðimýri, although
C. Lyngbyei only grows to a small height there. There are fairly
extensive mudflats along the shores of the lake, which are inun-
dated by the glacial rivers whenever they are swollen. You en-
counter the sociations of the flæðimýri, mostly the Catabrosa so-
ciation, in the most elevated part of the mudflats, next to the vege-
tated terrain. The first traces of vegetation there are sparse tufts of
Catabrosa, hut where the soil is firmer it forms continuous vegeta-
tion covers, either on its own, or with Ranunculus hyperboreus
where the clay is rather damp and loose; cf. sociations 8T-85 which
are intertwined there in various ways. E. Scheuchzeri has become
dominant in analysis XIX. 8 and there are sparse occurrences of
E. angustifohum. Agrostis stolonifera is rather conspicuous and C.
Eyngbyei and C. nigra are encountered there, and in places also
Calamagrostis neglecta. The third vegetation stage is shown in Tab.
XIX. analysis 9 where E. angustifolium is dominant, both in physi-
ognomy and covering. Calamagrostis neglecta rates high in fre-
quency, but otherwise not prominent. C. Bigelowii is also conspicu-
ous since we have now moved into the E. angustifolium flói which
is vexy extensive in Hvítámes. C. Bigelowii is most prominent down
by the mudflats, this area being somewhat drier than the flói
proper.
The same, or a very similar succession may be traced in Kaldi-
dalur, cf. above, where we commence with a Catabrosa aquatica
sociation which is replaced by an E. Scheuchzeri — Agrostis sto-
lonifera sociation, and finally an Eriophorum angustifolium flói.
It appears to me that where the bottom layer is glacial clay or sand
mixed with humus the first evolutionary stages of the vegetation
are of the kind which has been described above, and the final stage
is Eriophorum flói. When the bottom layer on the other hand is
oiadc up of pure sand, the first stage is an Equisetum arvense so-
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