The bleaching event that devastated much of the Great Barrier Reef in recent months made it clear that Earth's ecosystems are in crisis, driven to the brink by rising temperatures, pollution, and habitat loss. While there is a tendency to regard this situation as a product of the past century, the reality is that almost every environment on Earth has been irrevocably altered – or destroyed – by humans over the past 10,000 years. And although our impact on the oceans is occupying our minds at present, it is probably forests that have been hit the hardest. Whereas forests once covered much of the Earth, intensive exploitation by humans has destroyed almost eighty per cent of old-growth forests and radically reduced the complexity and diversity of what remains. Nowhere is this process more evident than in North America, where ninety per cent of the forests have been cleared in the four centuries since European settlement.