Arctic plant ecology: From tundra to polar desert in Svalbard - Unis

Our results suggest that: species diversity, on a landscape as well as local scale,
decreases in relation to bioclimatic zones (from C to A); whereas the number of
species in different vegetation types remains fairly constant throughout the Arctic.
Data on ecological amplitude were collected for 67 vascular plant species (Lang, Dees
and Bockmühl). The most important factors determining distribution of plant species
in Svalbard were pH and bioclimatic zones. There was no species with a pH
amplitude ranging from low to high pH tolerance in bioclimatic zone C, but one and
three in bioclimatic zone B and A, respectively. The ecological amplitude of the
species found in Svalbard were within the range recorded in Greenland (Böcher 1963,
Gelting 1934, Raup 1965, Raup 1969, Sørensen 1933, Karlsen & Elvebakk. 2003). A
minority of species was found to be widely spread and covering a wide amplitudes
regarding pH. The majority of the species studied possessed narrow to medium wide
amplitudes regarding pH, yet they were widespread on Svalbard. No significant
correlation was found between the number of localities where the species was found
and the potential distribution area based on substrate type. Thus, the hypothesis that
widespread species possess a wide ecological amplitude was rejected.
On the glacier forelands in bioclimatic zone C and B, the flora differed on moraines of
different ages (Vik, Aarnes and Müller). Thus, these glacier forelands follow the
succession pattern of species substitution with time as observed in other studies
(Moreau 2005, Hodkinson & Coulson 2003, Jones & Henry 2003). In bioclimatic
zone A however, the vascular plant flora of the moraines were very similar
irrespective of moraines’ age and no clear succession pattern could be found. Species
richness increases in bioclimatic zone C and B with time whilst in bioclimatic zone A
it was comparatively constant. The vegetation in bioclimatic zone A is scattered and
often consists of only single, individual plants. Thus, these marginal populations of
vascular plants rarely develop beyond initial succession phases (Svoboda & Henry
1987). To our knowledge, no other glacial forelands in bioclimatic zone A have been
studied, but we expect that lack of clear, successional stages is a general feature of
glaciers forelands in such extreme environments. The high arctic species Minuartia
rossii, Festuca hyperborea and Poa abbreviata were not found on the glacier
forelands. More glacier forelands should be investigated to see if these habitats could
provide a refugia, at least temporary, for these species in a warmer climate.
Measurements of 778 individuals of 19 different vascular plant species showed a
decrease in plant height, leaf size, and biomass from bioclimatic zone C to A
(Morgner and Pettersen). There was a positive correlation between plant height, leaf
size, and biomass with temperature, as well as nutrient availability. However, there
was also a significant interaction between temperature and nutrient availability in their
effect on plant growth. Increased nutrient levels seemed to compensate for the growth
limiting effect of temperature in bioclimatic zone B and C, but not so in zone A. Thus,
this study provides support to the hypothesis that high nutrient availability can
compensate for the growth limiting effect of low temperatures, but at the thermal limit
for plant growth, temperature itself sets the limit rather than nutrients. Further support
for this hypothesis was evident from the biomass samples. The biomass per unit land
area of full cover plots declined slightly from bioclimatic zone C to A, and bird cliffs
showed much higher biomass than nearby reference sites. The relative fertilizer effect
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