I just watched a documentary about the Pleistocene Valley in Siberia where groups are working hard to return the valley to its natural state. When Mammoths ruled the land, it was a grassy valley but at some stage became forested and the mammoths died out. The Pleistocene Park is being returned to that natural grassy valley and has been populated with native species of reindeer, yakutian horse, moose, bison, musk ox, kalmykian cow, sheep, camels and goats.

The area is ripe with the remains of mammoths and over the last decade, scientists have been working to create mammoth hybrids (mammoth x elephants) to introduce into the park. If they can succeed in bringing them back, then the region will have been returned to it's original state.

Another reason for this is to help fight climate change. The area is thick with permafrost which the forests have been destroying. The theory is that by bringing back native species, that will protect the permafrost which will in turn help save the Arctic tundra and glaciers. With the current wildlife, it seems to be working, but they really want to complete the project by bringing back the mammoths.

For some context, mammoths were still walking the Earth when the Newgrange tombs were being built in Ireland, c. 2000BC, so their extinction wasn't too long ago in the greater context...