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

processed within 24 hours. Equal amounts in volume of both soil and deionised water
were mixed in a flask. After repeated shaking for 1 hour, pH was measured by using
an electronic pH­meter. The pH values were divided into three categories of low (<
5.2), medium (5.2­7.0) and high (> 7.0) pH. This division corresponds to Karlsen and
Elvebakk (2003). The definition of substrates follows the preliminary substrate map
of Svalbard (Arnesen, personal communication). Raup did not include pH­
measurements in his study at the Mesters Vig district. Data from Karlsen & Elvebakk
(2003) were used for the Svalbard ­ Greenland comparison.
The soil moisture within each plot was assessed according to Raup (1969) by feeling
the soil with the fingers. Following categories were used:
1. low (dry, no feeling of dampness to the fingers)
2. medium (moist, wet the fingers when handled)
3. high (wet, water can be squeezed from the soil)
4. very high (wet, water is freely dripping from soil sample)
The disturbance gradient was separated into two categories established by Raup
(1969). He distinguished between frost disturbance (sorted or non­sorted circles) and
non­frost disturbance (erosion, slope instability). Although being a frost­initiated
process, Raup included solifluction into the non­frost disturbance processes since
plant roots are located in the upper layer of the sliding soil and thus not disturbed by
the slow soil movement. The categories for both frost and non­frost disturbance were
divided into:
1. stable (no visual disturbance, no bare ground)
2. medium (bare ground visible indicating cryoturbation and enabling erosion)
3. unstable (bare ground dominating, active cryoturbation or erosion, no
consolidation of soil recognisable)
Statistical analysis
To find the main abiotic factors determining species distribution, a DCA, CA and
CCA ordination were carried out using Canoco (Canoco for Windows 4.5, 1999). Hits
per species obtained by the point intercept method were used as the species factor.
Environmental factors included pH, soil temperature, organic soil depth, moisture,
frost and non­frost disturbance and total vascular plant cover. For ordination the
values and not the categories for pH and organic soil depth were used. Since soil
temperature was measured only once at each site being strongly dependant on current
weather conditions, bioclimatic zones A to C were used to replace soil temperature in
a second ordination. Bioclimatic zones are defined as subdivisions of the Arctic
reflecting climatic gradients (Elvebakk 1999). They integrate climatic measurements
over a longer time period thus greatly improving the comparison between the different
localities used in this study. The dummy variables for bioclimatic zones were
numbered 1 to 3 for zone A to C according to rising temperatures. Subdivision of
arctic reflecting climatic gradients.
We assumed that the species was temperature dependant so we wanted to test whether
soil temperature could be a factor differing between plots. Differences in soil
temperature for the plots at Colesdalen where E. wettsteinii was growing compared to
the plots excluding the species were tested by carrying out a t­test using S­Plus® 6.2
for Windows (Insightful Corp. Seattle, WA, USA, 2003).
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