Palearctic

The Palearctic (or 'Palaearctic') ecozone is one of the eight dividing the Earth's surface.
The Palearctic is by far the largest ecozone. It includes the terrestrial ecoregions of Europe, Asia north of the Himalayan foothills, northern Africa, and the northern and central parts of the Arabian Peninsula. 
Major ecological regions.
The Palearctic ecozone includes mostly boreal and temperate climate ecoregions, which run across Eurasia from western Europe to the Bering Strait.
Euro-Siberian region.
The boreal and temperate Euro-Siberian region is the Palearctic's largest biogeographic region, which transitions from tundra in the northern reaches of Russia and Scandinavia to the vast taiga, the boreal coniferous forests which run across the continent. South of the taiga are a belt of temperate broadleaf and mixed forests and temperate coniferous forests. This vast Euro-Siberian region has many shared plant and animal species, and many similarities with the temperate and boreal regions of the Nearctic of North America. 
Eurasia and North America were often connected by the Bering land bridge, and have very similar mammal and bird fauna, with many Eurasian species having moved into North America, and fewer North American species having moved into Eurasia. 
Many zoologists consider the Palearctic and Nearctic to be a single Holarctic ecozone. The Palearctic and Nearctic also share many plant species.
Mediterranean Basin.
The lands bordering the Mediterranean Sea in southern Europe, north Africa, and western Asia are home to the Mediterranean basin ecoregions, which together constitute world's largest and most diverse mediterranean climate region of the world, with generally mild, rainy winters and hot, dry summers. The Mediterranean basin's mosaic of forests, woodlands, and scrub are home to 13,000 endemic species. "Conservation International" has designated the Mediterranean basin as one of the world's biodiversity hotspots.
Sahara and Arabian deserts.
A great belt of deserts, including the Sahara desert, and Arabian desert, separates the Palearctic and Afrotropic ecoregions. These desert ecoregions are included in the palearctic ecozone; other biogeographers identify the ecozone boundary as the transition zone between the desert ecoregions and the Mediterranean basin ecoregions to the north. This would place the deserts in the Afrotropic, while others place the boundary through the middle of the desert.
Western and Central Asia.
The Caucasus mountains, which run between the Black Sea and the Caspian Sea, are a particularly rich mix of coniferous, broadleaf, and mixed forests, and include some temperate rain forest.
Central Asia and the Iranian plateau are home to dry steppe grasslands and desert basins, with montane forests, woodlands, and grasslands in the region's high mountains and plateaux.
The middle altitude foothills of the Himalaya between about 2000–2500 m form the boundary between the Palearctic and Indomalaya ecoregions.
East Asia.
China, Korea and Japan are more humid and temperate than adjacent Siberia and Central Asia, and are home to rich temperate coniferous, broadleaf, and mixed forests. These are now mostly limited to mountainous areas, as the densely populated lowlands and river basins have been converted to intensive agricultural and urban use. 
East Asia was not much affected by glaciation in the ice ages, and retained 96 percent of Pliocene tree genera, while Europe retained only 27 percent.