Simplify the following text for a Grade 8 native English-speaking person.
Original: Domesticated reindeer are mostly found in northern Fennoscandia and Russia , with a herd of approximately 150-170 reindeer living around the Cairngorms region in Scotland . The last remaining wild tundra reindeer in Europe are found in portions of southern Norway .
Simplified: Because reindeer can live in very cold climates , domesticated reindeer are used in most northern parts of the world .