Fróðskaparrit - 01.01.2006, Síða 129

ÚTBREIÐSLAN AV LÍVSHÆTTUM RAUNKIÆRS
NIÐAN EFTIR FJALLASÍÐUM í FØROYUM
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To investigate which of the environ-
mental parameters explained most of the
variation, we compared the F values from
the ANOVAtables (Figs. 4-7). Based on this
criterion, total vegetation cover best ex-
plained the variation of hemicryptophytes
and therophytes while temperature best ex-
plained chamaephyte variation and LOI
gave the highest F value for geophytes.
Discussion
All the results are based on life-form abun-
dances, which have been weighted so that
the sum of all abundances for each meso-
Plot is 100%. This methodology has the
drawback that the abundances of different
dfe-forms are not independent. If some life-
^orms increase in relative abundance, others
tnust decrease. Our main reason for choos-
lrig this strategy is the problem arising from
the highly eroded areas that dominate parts
°t the Faroese mountainsides, associated
'vith the decreasing vegetation cover with
ahitude (Table 3). By weighting the life-
form abundances in the specifíed manner,
tvc reduce the influence of vegetation-free
areas on life-form abundance values.
Altitude does not appear to be the best
Parameter to account for the variation in
ahundance of all Raunkiær’s life-forms
a'°ng an altitudinal gradient. As seen from
°ur results, total vegetation cover is corre-
lated almost as strongly as altitude with the
variation in abundance of hemicryptophytes,
hie most common life-forin in the Faroe Is-
lands. In relation to the other life-forms, we
l°und that hemicryptophytes decrease lin-
carly to the highest point on the gradient.
I his could, however, also be explained by
the fact that total vegetation cover decreases
similarily with altitude.
The decrease of hemicryptophyte abun-
dance with altitude was also found in grazed
areas at high altitude in Australia by Mcln-
tyre et al. (1995). They found that increas-
ing soil disturbance resulted in a decreasing
number of species with vegetative repro-
duction, but no effect was seen on species
without vegetative reproduction. This was
verified in our study with the negative cor-
relation of total vegetation cover on the
abundance of hemicryptophytes. In other
studies, hemicryptophytes were found to be
less tolerant of grazing than species with
subterranean over-wintering buds (Fladar et
al., 1999; Sternberg et al., 2000).
The most important parameter describ-
ing the distribution of therophytes is also
total vegetation cover. Fellfields, screes and
other areas with unstable soils such as pat-
temed ground are widespread in the alpine
zone in the Faroe Islands (Fosaa, 2004). In
such unstable habitats, therophytes are the
dominant life-form, with Koenigia islandica
as the predominant species, commonly
being the only species in our meso-plots. In
the Faroe Islands, the mountains are grazed
from the lowlands to the mountaintops,
(Brattaberg, pers. com.). Increasing distur-
bances due to natural causes also result in
decreasing total vegetation cover with in-
creasing altitude (Table 3). Soil disturbance
has been found to reduce the species rich-
ness (Mclntyre and Lavorel, 1994), which
is also consistent with our results. Mclntyre
et al. (1995) found that light grazing in-
creases diversity, while heavy grazing result
in a higher proportion of therophytes. The