It is no small thing to say that forests have an important role in the health of the planet. Aside from being a source of paper and fuel, trees are the second-largest contributor to all of the earth's oxygen, second only to the ocean. But forests as we know them are always at risk. Half of the forestry that the earth has lost since the last ice age has occurred in the past 100 years, thanks largely to industrialization and agriculture. But where are the world's biggest forests located? And how big are they compared to all land on earth?