Trees are often thought to be the good guys when it comes to climate change. In Siberia, however, it's not always the case. The landscape was changed when humans arrived and the forest that took over from grasslands is causing problems. In Pleistocene Park, Russian scientists are carrying out a radical rewilding - removing trees and reintroducing species of grazing animals to help protect the permafrost - the deep frozen ground - from thawing and releasing methane into the atmosphere. Tom Heap and Dr Tamsin Edwards consider how this ambitious idea could help in the fight against climate change. Producer : Anne-Marie Bullock Series made in partnership with the Royal Geographical Society