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The arctic tundra represents only a low scale of 1 of Norway but it is not less important. It has some features in common with Alpine tundra and it is found above the tree lines. We may found this ecosystem in extreme north of Norway with Southern Arctic zone of tundra but it is mainly represented in Svalbard, an island of Norway which is dominated by glaciers at 60%. Usually the scientist delimits the arctic zone with the isotherm limit of 10Â°celsius in July. There are different zones of this tundra, Southern Arctic zone of tundra, middle-zone and the high-zone, also divided in subzone recently established, A to E with A the coldest and E the warmest subzones (Jónsdóttir, 2005). The cold climate composing this ecosystem is mainly explain by its high latitude which receive low light, due to low angle of incidence, low moisture and precipitation, and a high albedo effect of the snow. The arctic tundra is particularly young in occupied the land for only 2000-10,000 years (Bliss et al. 1973).
In these arctic regions Permafrost is a soil characteristic in maintaining soil to 0Â°celsius for at least two consecutive years (Juliussen et al., 2010). It is composed of an active layer (30-50 cm) of mineral and organic soils with a depth of 200 cm in well drained sands and gravels that unfreeze during summer to enhance vegetation's growth (Brown, R .J. E., 1972) and a massive ice layer; both in low-Arctic and high-Arctic (Bliss et al. 1973). The temperature of this permafrost is very useful; it has been identified as one of indicators of climate change by the Global Climate Observing System (GCOS). An important long-term monitoring has been launched by the international permafrost association (IPA) with the international Polar year (IPY) in 2007-2009: research project Permafrost Observatory Project: a contribution to the Thermal State of Permafrost (TSP). The scientists have computed ground temperature by boreholes and also temperature monitoring in the air, snow cover, at the ground surface and/or in the upper ground. Nowadays, this vast monitoring continues. In Norway, the permafrost observatory project: contribution to the thermal state of permafrost in Norway and Svalbard (TPS NORWAY) use observatories in the two northernmost counties of Troms and Finmark and in central western Svalbard (Juliussen et al., 2010). All these research has allowed to establish a map of permafrost occurrences. The permafrost in Svalbard is continuous while in the mainland it is occur only in mountain areas.
According the vegetation cover, the arctic tundra is generally composed of shrublands, wet sedge and grasslands, herbfields, steppes. It is a simple and fragile ecosystem with low energy budget, in part due to its tough climate and its soil composition poor in nutrient.
In the mainland of Norway, the arctic tundra zone is represented in low-level between northern boreal and middle arctic. Usually it is characterized by a Podzol soil with an acid pH and a vegetation cover resembling to the low alpine zone. This soil is composed of humified organic component materials associated with aluminum and FER. They occur most often in areas with sandy materials cold and damp climate, in a forest or shrub vegetation. In despite of rigorous climate it exist an important flora which persist throughout the year with approximately hundred species of vascular plants and many cryptograms. This tundra vegetation is composed only of dwarf shrubs species such as willows, Alnus, Betula and Dwarf birch. As a result of frequent snow cover and the length of seasons reduced, only the rapidly developing plants can persist. Lichens, mosses and liverworts are common as well as Juniperus, Empetrum, Vaccinium species. We may found in this area several adapted mammals: reindeers, mountain hares, lemmings, stoats, weasels and voles and many migratory seabirds.
As see previously in Norway the mainly part of arctic tundra is in Svalbard, an archipelago at the north-western edge of the Barents Sea. This region has slightly different features due to its island characteristics. This archipelago has relatively mild climate in its western part because of the warm North Atlantic current reaching Spitsbergen, the largest island; whereas its east cost is reaching by a cold Barents Sea waters. Consequently there is large heterogeneity through islands from Arctic polar desert and northern Arctic tundra (high-zone) and middle Arctic tundra. During the last ice age Svalbard was almost completely covered by ice. Therefore, soils take long time to develop, and in comparison to the "mainland" there is a low species diversity on Svalbard, and terrestrial food webs are simple with strong links to marine food webs but in the other hand it is composed of unique biological communities. For example, birds play an important role in soils composition. Where the coast habitat allow seabird breeding colonies with cliffs, their guano contribute to a well nutrient availability and increases productivity and soil organic for plant community (Jónsdóttir, 2005). Moreover a study of Hodkinson and Coulson (2004) showed an important level of complexity of invertebrates' community in food webs. The vertebrates present on this archipelago are common to the Arctic ecosystem and adapted to its conditions, which allowed an important food sink for other species.
In this terrestrial food web, the Arctic Fox (Alopex lagopus), Glaucous gull, Arctic skua and Polar bear (Ursus maritimus) are the top predator, encompassing also the Snow bunting, Ptarmigan, Geese specie and the endemic Svalbard reindeer (Rangifer tarandus platyrhynchus). There are a low number of birds species, the most are seabirds such as Svalbard rock ptarmigan (Lagopus muta hyperborean), Atlantic puffin (Fratercula arctica), and Snow bunting (Plectrophenax nivalix). Some species were introduced but remain in small population such as the mountain hare (Lepus timidus), the arctic hare (L. arcticus) and the musk ox (Ovibos moschatus) now extinct. According to the plant community, only few areas have vegetation cover of low shrubs: Salix, Dryas, Herbs, Graminoids, Mosses and Lichen are the most vegetal species.
In consequence, some disturbance may affect this fragile equilibrium in this kind of ecosystem. In this area the human disturbance is relatively low but due to its fragility even vehicle tracks may affect it because of the slow re-colonization and growth rates of the ground organisms, plants and fragile soil structure. However, the current major disturbance is the long-term climate change especially for its particularly location and current water implicates. An expansion of species with warmer conditions or invasive species may also be harmful.
At higher scale, the global changing affects particularly the permafrost. Indeed, several studies showed an increasing permafrost temperature (Juliussen et al., 2010).
The scientists predict in the future serious consequences of global warming on permafrost. Lars Kullerud, director UArtcic and Svein Tveitdal reports and warns about the consequences of the permafrost melting for the United Nations Environment Programme (UNEP):
1) Permafrost areas will be reduced, in southern Norway it is not continuous anymore as the northern hemisphere and scientific models from IPCC predict a possible reduction of up to 16 per cent the next 50 years in these discontinuous permafrost. 2) Danger to indigenous people and ecosystems 3) spreeding up the greenhouse effect: the tundra has worked as a carbon sink; carbon dioxide is released and it is mostly released as methane, because the rotting process is happening in wet soil with little or no supply of oxygen. A Huge water quantity will released leading ground erosion. That's why many studies are conducted to monitor and predict these changes in Svalbard and other part of the Arctic polar zone.
The alpine tundra as arctic tundra occur above the tree line, either in high altitude in mountainous regions or above 60Â°N latitude in Northern Norway until approximately 70Â°N where it become arctic zone. Norway is covered by approximately 48% (148000 km2) of mountains (Abrahamsen et al., 1977) and Alpine tundra covers large areas: 32% of land area, including Hardangervidda, a famous plateau in Norway, which is the largest European plateau entirely located beyond the treeline with an alpine tundra.
Among these latitudes it is difficult to distinguished Alpine or Arctic tundra. However, Alpine tundra benefits warmer climate and longer season. In opposite of arctic tundra one feature is remarkable: the habitats are more fragmented, then plant and animals disperses less rapidly. Consequently the species and genetic diversity are more important in this area.
This tundra is also divided in low-alpine, mild-alpine and high-alpine. The low-alpine occurs in low-altitudes nearby the treeline with diverse plants as the willow species, blueberry, common juniper and twinflower, but meadow and moorlands plants dominate these areas; whereas mid-alpine has smaller plants such as mosses and lichens, similar to low-arctic species but the ground is most cover even if the snow cover last into mid-summer. Then, the high-alpine tundra looks like more that arctic tundra with bare rock, snow and glaciers encompassing only few plants species (norway infoe3, 2010) such as the glacier crowfoot (Ranunclus glacialis), the drooping saxifrage (Saxifraga cernua) and the moss campion (Silene acaulis). Therefore, Alpine tundra has several features in common with arctic tundra, thus its fauna share many similarities with low-arctic fauna: reindeer, mountain hare, lemming, stoat, weasel and voles are common species. The most of these species live also under the tree line, only ptarmigan (Lagopus mutus) bird's specie seems to live only above and other birds species migrate in high latitude towards arctic zone such as willow grouse (L. lagopus).
The high latitudes ecosystems as Alpine and Arctic tundra are in general more sensitive and vulnerable to environmental changes. Löffler and Pape (2008) suggested that they seem to be the most sensitive to climatic changes occurring on a global scale.
The Alpine tundra occurring in mountains is largely use for grazing of sheep and reindeer (wild and semi-domesticate) since a long time ago. Although nowadays their populations are controlled by hunting management, and sheep grazing is mainly restricted to southern Scandinavian (Norwegian) mountains, where sheep share their habitat with the wild reindeer at several sites, they remain a significant disturbance (e.g. in Hardangervidda-Nordfjella, Rondane-Dovrefjell and Setesdalen) (Austrheim & Eriksson, 2001). Indeed, they have a significant effect on the alpine tundra. This grazing has several effects and may be as well as positive or negative for the species diversity. Yet, overgrazing is in most case harmful for the ecosystem dependent of regional pattern: soil features, abiotic factors (c.f. pH), productivity, and distribution of snow, temperature, species pool and degree of fragmentation. Austrheim & Eriksson (2001) conclude that control of grazing is a key process for maintaining biodiversity in the Scandinavian mountains. The rodent and their strong grazing following their cycle have also an important impact and these ecosystems (Austrheim & Erikson, 2001). All these effects act at larger scale in the other part of tundra (alpine in Northern latitudes and arctic tundra). A study from Hofgaard (1997) provides more details about these effects and highlights on the inter-relationships of these two factors with an effect more pronounced of the diminished grazing on vegetation responses than changing climate.
Moreover, as see previously the climate change is also an important factor at high latitudes, especially in act on snow cover and glaciers. Davis (1986), Pauli et. al. (1996) showed that species community equilibrium (animal and vegetal) is affecting by the climate change with time lags, often with populations density increases at the summit which lead to problems of space and competition. Although they describe also an increasing of species diversity, we may predict with such effects in the future, extinction of some sensitive species because of the warmer climate. Furthermore, it is also important to take in account an increasing tourism. Svalbard archipelago attracts more tourism each year, a lot of cruise tourism and expedition disturbed the sensitive ecosystem trough many ways: wildlife disturbance, degradation of vegetation, pollutions despite protected area and laws (WWF, 2004).
Some consequences of these changes are already clearly remarkable: the shrub expansion in tundra ecosystems is a good example. Indeed, as view previously we can found this species in both ecosystems but at quite small scale or under different form (normal or dwarf).
Yet several recent studies showed net changes, particularly Myers-Smith et.al. (2011). They used repeat photography and long-term ecological monitoring and they found a significant increasing of shrub abundance at the circumpolar Arctic, high latitude and alpine tundra because of a warmer climate and changes in snow cover. This may fundamentally change and alter the structure of biotic components such as energy fluxes, soil, carbon and nutrients cycles, and ecological interactions between species.
That is why understanding the mechanisms that control diversity are necessary for predicting changes from land use and changing climate.