Biodiversity in the High and Mid Arctic

The High and Mid ecoclimate province of the Arctic is found in northernmost Canada, Greenland, on Svalbard (Norway), and in areas of the Russian Arctic such as Novaya Zemlya and the Taymyr Peninsula. The High and Mid Arctic (or Arctic and typical tundra in Eurasian terminology) are characterized by discontinuous vegetation cover and low biodiversity. Plant cover usually ranges between 15% and 75%, depending on the supply of soil moisture, local topography, and climatic conditions. Large areas in the High and Mid Arctic are covered by barren polar deserts and polar semideserts. In addition to Greenland's immense icecap, large areas of Devon Island, Ellesmere Island, and Axel Heiberg Island in the Canadian High Arctic are covered by glaciers. Yet even in the polar desert of the High Arctic, so-called "polar oases" can be found, which have a more or less continuous cover of sedge meadows and play an important role for local wildlife. In the High Arctic, the mean annual precipitation is low, approximately 130 mm per year. Mean daily temperatures exceed 0°C only in July and August, while daily winter temperatures average below -30°C. Towards the Mid Arctic, climate conditions improve, tending to become more humid with marginally longer growing seasons.

In the High and Mid Arctic, vegetation in very moist sites is composed of Eriophorum (cottongrass) and Carex spp. (sedges). Salix, Dryas, and Saxifraga species usually dominate in moist but drained sites as well as in drier locations with low cover. Over 120 vascular plant species occur in the High and Mid Arctic. Net annual plant production is low. Production estimates of 1-2 g cm-2 in polar desert sites and 20-40 g cm-2 in cushion plant-lichen communities reflect the extremely low production capacity. Yet, occasionally wet sedge-moss communities have been found to produce as much as 300 g cm-- . Low above-ground to below-ground phytomass ratios are characteristic of Arctic tundra ecosystems, with the top-to-root ratio generally decreasing with increasing mean annual temperatures.

In the High Arctic, only a few mammals are able to maintain viable populations. Muskox, Peary's caribou (Rangifer tarandus pearyi) (a northern subspecies of the barren-land caribou), Arctic hare, collared lemming (Dicrostonyx groenlandicus), Arctic fox, wolverine, Arctic wolf (Canis lupus), and the polar bear (Ursus maritimus) are among them. Peary's caribou differs from the barren-ground caribou in being smaller and much paler in color. The High Arctic population is listed as endangered and can exhibit marked population collapses, depending on snow conditions during the winter. Natural populations of muskox occur only in the Canadian Arctic and Greenland. In Canada, muskoxen are found on the Arctic mainland and on the Arctic Islands, with Banks Island and Victoria Island having the largest populations. Greenland's muskox population is found in the north and northeast of the island. They have also been introduced to other regions, for example Québec in Canada, Norway

(including Svalbard), Russia (Wrangel Island and Taymyr Peninsula), and Alaska. Muskoxen are the major prey of Arctic wolves—besides caribous, lemmings, and Arctic hares. Since availability of prey is restricted and distributed heterogeneously, wolves have to cover great distances in search of food.

For land mammals, winter is a difficult season. Consequently, in all species, winter coats are thicker and longer-haired than summer coats. Some species such as caribou and polar bear have hollow, air-filled hairs that provide exceptionally good insulation. Long-term population cycles are typical for some Arctic land mammals. The three- to four-year population peaks of the brown lemming (Lemmus sibiricus) are typically asymmetrical, with populations declining at a greater rate than they increase. There is strong evidence that these population cycles are caused by plant-herbivore interactions rather than by predator-prey or plant-environment interactions.

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