Forest cover is the amount of trees that covers a particular area of land. It may be measured as relative (in percent) or absolute (in square kilometres/square miles). Nearly a third of the world's land surface is covered with forest, with closed-canopy forest accounting for 4 - 5 billion hectares of land.[1] Forests provide many ecosystem services that humans and animals cannot survive without, but anthropogenic actions and climate change are threatening global forest cover in potentially irreversible ways.