Britannica Sources used in this answer

Why are the Nearctic and Palaearctic regions sometimes combined into the Holarctic region?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

World map using color coding to show the distribution of major floral kingdoms, subkingdoms, and regions. Key floral kingdoms include Boreal (green), Neotropical (pink), Paleotropical (yellow), South African or Capensic (purple), Australian (orange), and Antarctic (blue). Boundaries for subkingdoms, regions, and divisions are marked with different colored lines, and major regions such as Indoafrican, North American, and Malesian are labeled across continents. — biogeographic region Floral kingdoms, subkingdoms, and major regions of the world.

The Nearctic (North America and Greenland) and Palaearctic (Eurasia and northern Africa) regions are often combined into the Holarctic region because of the significant historical interchange of fauna between them.12

This biological connection was facilitated by a land bridge that periodically linked Siberia and Alaska during periods of worldwide glaciation and lowered sea levels. Known as Beringia, this land connection allowed for the migration of plants and animals between the Old and New Worlds. Because of this shared history and the resulting similarities in their characteristic animal life, zoogeographers frequently group these two regions together as a single biogeographic unit.23415