Polar desert

Polar deserts comprise stone- and gravel-dominated areas north of or at elevations above the Arctic tundra zone where the vegetation cover is fragmentary owing to low temperatures and where woody plants and sedges are lacking. This is a circumpolar arctic habitat type that has in common with the ‘true deserts’ that precipitation is extreme low (< 200 mm yearly) and the vegetation growth period is very short. Around the Isfjord on Svalbard, an area very positively affected by the north atlantic current, the growing season for example is about 40-50 days. The habitat is characterized by extreme low summer temperatures (< 2 °C mean summer temperature, considered as the most important abiotic factor), shallow soils over permafrost (which is instable due to cryoturbation, causing honeycomb soil patterns), and little relief (resulting in low snow cover). Polar deserts consist of fine to medium coarse substrates resulting from frost weathering processes with particle sizes ranging from silt to gravel and stones. The sediment in most sites is calcium-rich, but acidic bedrock may occur as well. Polar deserts are restricted to continental areas influenced by cold sea currents from the Arctic Ocean.

The habitat has in general a very low vegetation cover (1-10%) or is in some areas completely free of plants. Species characteristic for Polar deserts are Cerastium nigrescens subsp. arcticum, C. regelii, Draba pauciflora, Luzula confusa, Papaver dahlianum, Phippsia algida, Saxifraga hyperborea and S. oppositifolia, which usually grow scattered. In between mosses and crustose lichens may be found in rock crevices; these are mainly wide-spread species. Locally, plant cover in Polar deserts may be increased owing to favourable abiotic conditions. For instance, at sites better protected from wind and frost, species like Stereocaulon rivulorum and Phippsia algida may be abundant. Increased nutrient input in areas colonized for long time by reindeer, like on the plateaus of Edgeøya, may enable an increased growth of byrophyte mats dominated by Tomentypnum nitens. Such areas, although in the climatic region of the polar desert, are considered Moss tundra habitat (F1.2). Some of the polar desert species (Luzula confusa, Papaver dahlianum, Phippsia algida) also grow in slightly warmer climates, in habitats with little competition with other species.

Polar deserts are typically found in the flat or slightly undulating lowlands and on mountain plateaus of eastern and northern Svalbard, and on glacier free parts of the Russian islands in the Barents Sea (Franz-Jozef-Land, Victoria islands and Nowaja Semlja). The mountains of these regions may have a similar plant species composition on scree habitats (type H2.1, H2.1). Moreover, Polar deserts occur all over Svalbard at elevations above 200 to 500 m a.s.l.  A difference with Moss and lichen tundra (F1.2) is the general lack of typical tundra species (e.g. Carex spp.) including woody species (e.g. Salix spp., Dryas octopetala and Silene acaulis).

Indicators of good quality: 

This is natural vegetation occurring in remote areas which are under limited human influence. It is generally rather stable, but may be threatened by global warming.

The following characteristics can be considered as indicators of good quality:

• Long-term stability of low vegetation cover
• Abundance of species sensitive to changes in soil moisture and temperature (like Draba adamsii, Cerastium regelii, Saxifraga hyperborea)
• Absence of long living and slow colonizing species indicating global warming, like Silene acaulis, Dryas octopetala, Salix polaris and Festuca rubra ssp. richardsonii

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats