Boreal forests, which are second only to the Amazon in terms of their vital role in ensuring the future of the planet, encircle the Arctic -- and they are in just as much danger from climate change as the South American rainforest. The deep, verdant green ring -- which stretches across Canada, Scandinavia, Russia and Alaska -- has been weakened by increasing forest fires, the melting of permafrost, intensifying insect infestations and warming temperatures. Experts are categorical in their warnings: the forest is encroaching on the tundra, and the prairies are slowly taking the place of the trees.