Fróðskaparrit - 01.01.1992, Side 51

THE EXOTIC LAND PLANARIAN . ..
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in 1976/77 from where it was further dis-
tributed, e.g. to the present arboretum in
1978/79 and from there to the Gundadalur
plantation in 1980’s (T.G. Leivsson,
pers.comm.). Many of the plant species
collected during the expedition to New
Zealand/Tasmania/Australia in 1974/75 (as
well as species collected during expedi-
tions to southem South America in 1975
and 1979) have survived in Tórshavn and
appear to have adjusted well to Faroese
conditions - especially so when compared
with the performance of plant material at
Hørsholm and Milde (Søndergaard, 1989).
Thus, it may be expected that those Faroese
conditions favouring the survival of New
Zealand plant material have likewise
favoured the survival of the land planarian
after its introduction.
Although the plant material originating
from New Zealand provides a possible
means for the passive immigration of A.
triangulata, this particular route seems less
likely as the material came to the islands in-
directly. Moreover, subsequent examina-
tion (also in November 1992) of the Danish
arboretum at Hørsholm where the New
Zealand plant material was originally prop-
agated (as well as the forest botanic garden
at Charlottenlund, Denmark, where some
of the New Zealand material was transplan-
ted) did not give any indication of the land
planarian. Nor are there any known sight-
ings of the land planarian at the Norwegian
arboretum at Milde.
Even so, although A. triangulata has not
yet been recorded in either Denmark or
Norway this does not exclude the possibil-
ity that the land planarian has reached these
countries via the arboreta at some stage
previously but prevailing conditions have
not allowed the species to colonise there.
With regard to the New Zealand plant
material, survival has been far better at
Tórshavn than at Hørsholm or Milde, these
differences in survival being best explained
by milder winters and shorter periods of
continuous frost at Tórshavn compared
with the other two localities (Søndergaard,
1989). Furthermore, the winters of 1981/82
and 1984/85 were among the coldest in
Denmark since 1900 (Rosenøm, 1986), and
those of 1978/79 and 1985/86 among the
coldest in West-Norway since the tum of
the century (Hjellestad, 1985) with the soil
frozen to a depth of more than one metre at
the Norwegian arboretum (Søndergaard,
1989). Thus, if A. triangulata had been
transported to Hørsholm or Milde with
plant material in 1974/75, it is unlikely that
the land planarian could have survived the
aforementioned extreme climatic condi-
tions that have occurred in Scandinavia
since. However, the possibility remains that
during the initial phase of plant propaga-
tion and re-distribution, Hørsholm and/or
Milde could have provided temporary habi-
tats for the land planarian and therefore
acted as stepping stones to the Faroe
Islands.
Faroese potato fields as an ideal habitat
The potato fields in Kvívík were notable in
that either high densities of earthworms
(>200 m 2) or high densities of A. triangu-
lata (approx. 40 adults/large juveniles plus
60 full egg capsules m-2) were found.