Rit (Vísindafélag Íslendinga) - 01.06.1975, Page 34

may be mentioned, all of which have their native hahitat in flói
vegetation. In addition there occur various species which actually
belong in drier parts of the flói or even on grassland.
It is of interest that this sociation embraces a greater number
of species than other flói sociations, which is in effect a common
characteristic of all observations from Flói, as is most clearly re-
vealed e.g. by comparing them with my observations in Melrakka-
slétta (Steindórsson 1936). Two factors are responsible. Firstly the
area in question is drier than flói tracts normally are. The bottom
layer everywhere consists of lava under a relatively thin peat
stratum and in average summers the land dries up somewhat. It
should also be noted that when the analysis was made a drying
effect in connection with the irrigated land was observed. Second-
ly, and this may be the overriding factor, the entire locality has
been affected by settlements. All the observations were made in
meadows because no other type of mire occurs there. The effect
exerted by haymaking in flói vegetation has already been alluded to.
The number of species and their composition in this sociation
strongly indicates the mýri. But here the topography is the deter-
mining factor. Eriophorum angustifolium never achieves domi-
nance in physiognomy or covering in mýri sociation and the
common accompanying species here, C. chordorrhiza and C. saxa-
tilis, seldom occur to any significant extent in the mýri. But this
sociation is a good example of the changes which take place in
vegetation, when the land dries out to some degree without losing,
however, the flói character. Such changes may also be observed
when haymaking is practised.
The biological spectrum reveals that geophytes are dominant as
elsewhere in the flói, but hemicryptophytes show a higher percen-
tage than is common elsewhere in the flói, which unmistakably
indicates the mýri. The E. species are decisively in a majority,
which all flói sociations have in common, especially the more
northern species E 4 and E 3. This clearly indicates that biological
conditions of the flói are most favourable to species which neither
require warmth nor are particularly tolerant of cold temperatures,
since temperature fluctuations in the soil of the flói are very slight.
The analyses were all taken at Breiðumýri in Flói. Analysis 1 is
from the border of the mire in an area between a pond and dry
34