Fróðskaparrit - 01.01.2006, Page 130

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DISTRIBUTION OF RAUNKIÆR’S LIFE-FORMS
ALONG ALTITUDINAL GRADIENTS IN THE FAROE ISLANDS
abundance of therophytes in the Faroes, in-
creased significantly with increasing alti-
tude, although the richness of this life-form
decrease (Fig. 3). This result is consistent
with Grime et al. (1988) and Mclntyre et
al. (1995) who found that therophytes in-
crease in areas with low total vegetation
cover and little competition from other
species.
We found that chamaephytes had their
Iowest abundance between 400-500 m, and
then increased with altitude. Geophytes in-
creased linearly with altitude. The most im-
portant parameters describing the abun-
dance variation of these two life-forms are
annual mean soil temperature and soil loss
on ignition, respectively.
Minimum chamaephyte abundance in
the mid-mountain slopes can be explained
by the disappearance of species such as Cal-
luna vulgaris, Empetrum nigrum, Vaccinium
myrtillus and V. uliginosus at the minimum
abundance altitude (500 m), and increasing
abundance of these chamaephytes above this
elevation. It can, however, possibly also be
the result of increased abundance of cha-
maephytes such as Silene acaulis and Salix
herbacea above this same elevation.
Studies from other areas showed that
geophytes are more resistant to grazing dis-
turbance than both chamaephytes and hemi-
cryptophytes, since their over-wintering
buds are subterranean and they flower early,
features which enables them to flower and
set seed despite grazing (Hadar et al., 1999
and Stemberg et al., 2000). In other studies,
geophytes were also found to decrease with
altitude (Danin and Orshan, 1990; Gomez
et al. 1993; Pavón et al., 2000). Since geo-
phytes in this study represent only 25 % of
the geophytes occurring in the Faroe Islands
(Fig. 2), it is difficult to draw any conclu-
sions about this life-form.
Conclusion
Retuming to the first question posed in the
introduction: How do life-form abundances
change with altitude in a quantitative man-
ner? We found a linear relationship between
altitude and three of the life-forrns.
Hemicryptophytes decrease linearly; thero-
phytes and geophytes increase linearly; and
chamaephyte abundance changes paraboli-
cally with a minimum at the mid-mountain
elevation.
The second question posed was: Is the
transition between temperate and arctic veg-
etation abrupt, or continuous, and, if the for-
mer, then at what altitude? We found a shift
in the abundance distribution of chamae-
phytes at 400-500 m a.s.l. The relative abun-
dance of chamaephytes increases in relation
to hemicryptophytes above this altitude.
This indicates a change from lowland tern-
perate vegetation, with hemicryptophytes as
the dominant life-form, to arctic vegetation
in the highlands where chamaephytes are
more abundant than at lower altitudes.
The third question was: What parameters
are responsible for the life-form changes and
to what extent are these parameters climatic?
Both non-climatic and climatic parameters
seem to be correlated with changes in rela-
tive abundance of life-forms. Chamaephytes
are an exception to this generalisation, as
they are not correlated to total vegetation
cover or LOI.
The high abundance of therophytes in the