As threats to wildlife and habitats go, the global expansion of farmland – including land used for crops and livestock – is unrivaled. Forests, grasslands, and wetlands representing more than two-fifths of the earth’s ice-free surface have given way to farming. Over the past half century alone, farmland has grown by more than 400 million hectares – an area nearly half the size of the United States. More than half of recent agricultural expansion in the tropics has come at the expense of old-growth forests. Conversion of natural habitats to farmland has been a leading cause of precipitous declines in terrestrial wildlife populations, which on average fell by more than half between 1970 and 2012.