Jökull - 01.12.1969, Blaðsíða 158

hk g/ho
HEYUPPSKERA I loo kg of hektara.
Fig. 11. Average yield oí hay in 100 kg
per hectare for the whole of Iceland (1943-
1967) and years of substantial winter kill-
ing of grass.
when sea ice lias been land-fast in the latter
part of winter, and also most in those districts
where sea ice has come right upto the coast.
Winter killing causes, and has caused, great
havoc to cultivated land, especially to level
hayfields. Such winter killing is frequently
mentioned in the older sources, ancl then
nearly always in connection with the colder
weather associatecl with sea ice.
During the last three sea ice years damage
from winter killings has been very substantial,
and in some areas it has been responsible for
an almost complete failure of the crop. With
an increase in the arrival of sea ice, together
with colder weather, we may therefore expect
even more widespread damage through winter
killing.
SEA ICE AND AGRICULTURE
We have mainly been concerned above with
the effects of sea ice on vegetation and at-
temptecl to describe how changes in tempera-
ture may affect the growth of grass. So far,
Icelandic agriculture has largely been basecl on
the use of the annual grass crop for livestock,
and the nation has to a greater or lesser extent
lived off the livestock products. If there is a de-
finite correlation between the arrival of sea ice
and annual temperature on the one hand, and
between temperature and grass growth on the
other, the correlation will be obvious between
grass growth and the well-being of livestock,
and consequently the well-being of the farmers
also. In other words, the sea ice has, through
its influence on weather and grass growth, a
1 54 JÖKULL 19. ÁR
considerable effect on the state of livestock.
This correlation may be shown further by a
comparison between the number of livestock
in the country at clifferent periods and the
frequency of ice years during the same periods.
The graph (Fig. 12) compares the numbers of
livestock in Iceland and the frequency of sea
ice years. This shows definitely some correla-
tion between the arrival of sea ice ancl the
numbers of livestock. It is, for instance, parti-
cularly noticeable that during the cold period
after 1860, when the graph shows the pre-
sence of much sea ice, there is also a de-
crease in the numbers of livestock in Iceland.
Much of the 20th century is ice-free, but the
increase in livestock is due not only t.o the
milder climate but also to the great improve-
ment in farming technique and methods over
previous centuries.
Bergthórsson (1966) has shown that, with a
deterioration in weather and a clecrease in
mean temperature for 10 months of the year,
the period in which both horses and sheep
have to be fed indoors is lengthened. In the
old records, the correlation is also obvious be-
tween sea ice years and a decline in the numb-
ers of cattle, horses and sheep. It is, therefore,
natural to ask, how close this correlation is
ancl how far the mean annual temperature
needs to fall in order that such a situation
be created in forthcoming years. Did the sea
ice formerly liave such a big effect on the
mean temperature of certain, specific months
or even of the whole year that it caused a
decline in livestocks, or was the misfortune due
merely to more primitive farming methods?
Would we, with the aid of modern technology,