The Botany of Iceland - 01.12.1930, Side 73

STUDIES ON THE VEGETATION OF ICELAND
63
The situation of these two formations in relation to each other
affords an excellent illustration of the relation to moisture of Arcto-
staphylos iwa ursi and Calluna vulgaris. On the heath of Jutland
we may similarly distinguish between a higher tract with Arcstosta-
phylos and Calluna and a lower tract where Arctostaphylos is absent.
Though the environment differs widely in the Icelandic mo and
the heath of Jutland, it is wortli noting that species which tliey
have in common react similarly to the same change of environment.
It is not the sum of environmental factors but the indi-
vidual factors of the environment which determine the
distribution of the species.
The Jaðar and Mýri Vegetations: Fig. 11 and table 15 A —13.
In areas where the degree of moisture is determined both by
the precipitation and the ground water we meet with those stretches
■which are called “mýrar” in Icelandic. Owing to the abundant
precipitation the mýri is very extensively distributed throughout the
Icelandic lowlands. Several types of mýri are found. Of most com-
mon occurrence is the »fórmýri« or swainpy mýri, formed in
cup-shaped depressions on Ievel or slightly inclined ground. Its for-
mation and peculiarities are due to the sour stagnant ground water.
Where the soil grows very damp, that is to say, where the ground
water covers the botlom all the year round, swampy stretches,
“floar” are formed. The second type of mýri is the »hallamýri” or
well mýri. This is formed where the ground water is pressed up
°ut of the soil, hence it is often seen at the foot of mountains.
Where the water is pressed up with such force that springs are
lormed and where the bottom is therefore swampy and damp all
the year round the “dý” vegetation is formed.
The third type of mýri is the “fétmýri” or irrorated mýri formed
°n tracts inundated b}r water for shorter or longer periods of the
year. Natural fétmýrar are thus formed on the banks of rivers but
niost extensively in deltas near the sea. The characteristic plant
ni this type of mýri is Carex Lynghyei, and since this plant is an
imporlant forage plant, successful damming experiments have latelv
been made with a view to creating conditions for an inundation
mýri in places where it was not formerly found.
Three different types of vegetation are associated with these
three types of mýri. I was afforded most opportunity for a thorough-
8°hig study of the swampy mýri which I investigated both in Lyng-