1.2.1 Arctic – a young biome with a dramatic history
The location of the Arctic within the Earth system combined with its particular climate history, have provided unique settings for the current flora and fauna to evolve, colonise, develop and interact. The overall species diversity and richness decreases when moving from the Equator to the Arctic and accentuates when moving from the low to the high Arctic (Ulrich and Fiera, 2009).
The Arctic tundra is a “young” biome, with a short evolutionary history compared to other large biomes such as boreal forest and temperate grasslands. During most of the Tertiary (ca. 2.5-65.2 million years ago) forests grew at high latitudes, e.g. in Canada and Greenland (McIver & Basinger 1999), and tundra did not appear until the global cooling in the late Pliocene (Murray, 1995; Zachos et al., 2001). Initially, tundra was distributed discontinuously, but became continuous about three million years ago (Matthews 1979). This global cooling was also the on-set of recurrent cycles of glacials and interglacials during the Pleistocene, covering most of North-America and Eurasia (Dyke, 2004; Svendsen et al., 2004).
The areas surrounding the Bering Strait, named ‘Beringia’ (Hulten, 1937), were the only extensive areas in the Arctic that remained unglaciated during this period (Dyke, 2004). During the glaciations, the global sea level was also much lower than today, turning the shallow Bering Strait into the Bering Land Bridge connecting Asia and North America (Hopkins, 1967; Elias et al., 1996). At least ten major glacial events happened throughout the Pleistocene. Glacier cover in the Arctic increased from the beginning of each glacial period, eventually covering large terrestrial extensions. Many terrestrial species occupied southern refugia during glaciations, but also ice-free refugia within the Arctic, like Beringia. At the end of each glacial period, on the other hand, animal and plant species were able to recolonize terrestrial ecosystems following warmer conditions and glacier retreat. The last glacial period, popularly known as the Ice Age, was the most recent glacial period within the Pleistocene glaciation occurring during the last 100,000 years of the Pleistocene, from approximately 110,000 to 12,000 years ago.
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