Divided between Europe, Asia and North America, the boreal forest biome, which covers 12 million km2, adapted to a cold climate and extreme temperature ranges. The ecosystem is dominated by coniferous forest, the vast majority of whose conifers retain their needles during winter. These needles are covered with a thick layer of wax that reduces water loss. Having persistent needles means that in spring, conifers are ready to start photosynthesis, whereas deciduous trees have to grow new leaves!