Oreal and Tundral Bioregions

High mountains above the tree line constitute the oreal biome, and treeless areas close to the poles form the tundral biome. The oreal and the tundral biomes are ecologically similar and often are considered together as oreotundral. This classification is particularly justified in view of contacts between the two realms during the Pleistocene. Treelessness is caused by cold temperatures and the short vegetation period, and sometimes also by exposure to wind. The Arctic tundral is a large zonal biome, and large areas have permafrost soil. During the short summer, the deeper soil never thaws; thus meltwater remains on the surface, leading to the establishment of extensive swamps and bogs. Low temperatures impede the rotting of dead plants, which are largely mosses, and peat formation is therefore common. Tundral areas in the Southern Hemisphere have no permafrost soil; they are highly fragmented and essentially restricted to the subantarctic islands. Insect biodiversity is low, especially in the tundral, and less so in the oreal.

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