Site description
On 6 August 2014, 25 Cassiope tetragona shrubs were sampled at a mesic tundra site (69.26 °N, 53.48 °W, 45 m above sea level [m a.s.l.]; Fig. 1a-c) located in the Blæsedalen valley about 2 km northeast of Arctic Station near Qeqertarsuaq on the southern tip of Disko Island, western Greenland. The area’s soils consist of basaltic rock fragments, covered by a 5–10 cm organic horizon, while active layer depths can reach 1.5 m . The geology of the area is characterized by a low bench of gneiss bedrock, Tertiary breccia and plateau lava . Shrub samples were collected in an area of approx. 60 m × 100 m. A minimum of 1-2 m distance was kept between sampling spots to avoid repeated sampling of the same shrub individual. It was attempted to sample complete (excl. roots) shrub individuals by following shrub branches until reaching the root-shoot boundary.
The vegetation at the site can be described as erect dwarf-shrub tundra, which covers 9.7 (13.7) percent, i.e. 689 × 103km2, of the (non-glaciated) Arctic . It is dominated by the deciduous shrub species Betula nana , Salix glauca , and Vaccinium uliginosum and the evergreen shrub speciesCassiope tetragona , Empetrum nigrum ssp.hermaphroditum , and less frequently, Rhododendron tomentosum . The climate at the site is Low-Arctic with a mean annual air temperature of -2.3 °C measured over the period 1994-2013 at ClimateBasis Disko , 3 km southwest of the site, and an interpolated annual precipitation sum of 330 mm over the same period (Fig. 1d). February was the month with the lowest mean air temperature (-13.0 °C) and March the month with the lowest mean minimum air temperature (-16.4 °C). July is the warmest month with a mean air temperature of 8.5 °C and a mean maximum of 11.4 °C. Mean monthly air temperatures remain below zero from November through April, hence most precipitation falls as snow. Frosts are likely to occur as late as June and as early as September (Fig. 1d). September is the wettest month with a mean precipitation sum of 39.6 mm and February the driest (16.1 mm).
The site is located on a gentle south-southeast-facing slope (Fig. 1e) at which C. tetragona is the dominant species (Fig. 1f). Further west near Ilulissat on mainland Greenland, the species is only found on north-facing slopes, while further south in the Disko Bay area, near Aasiaat, the species is absent at low elevations.