Explosive growth of secondary roads is linked to widespread tropical deforestation.

In the tropics and beyond, roads are key proximate drivers of environmental impacts, including forest fragmentation, fires, mining, and land clearing. Such impacts may be amplified for the initial roads constructed in intact forests-which we term "first-cut roads"-which often promote a rash of associated secondary roads branching off the new infrastructure. These secondary roads in turn can dramatically elevate forest and biodiversity losses.