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. Although widely seen as a conservation concern, the magnitude and effects of secondary road development have not been previously quantified. Without such information, impact assessment procedures for road projects risk misjudging the level of expected forest loss, hampering decision-making. Here we quantify the environmental impacts of both first-cut and secondary roads in three of the world's major tropical regions where high-quality road maps have recently become available: the Brazilian Amazon, Congo Basin, and New Guinea.

This dataset contains (1) the complete map of roads for New Guinea reported in Engert et al. (2024, Nature) and Engert et al. (2025, Current Biology); and (2) travel cost layers for the Brazilian Amazon, Congo Basin, and New Guinea that were used in network analyses reported in Engert et al. (2025, Current Biology). Methods for creating travel cost layers and their use is reported in Engert et al. (2025, Current Biology).

If using the travel cost layers, please reference Engert et al. (2025, Current Biology). If using the road map for New Guinea, please reference both Engert et al. (2024, Nature) and Engert et al. (2025, Current Biology).

Engert, J.E., Campbell, M.J., Cinner, J.E., Ishida, Y., Sloan, S., Supriatna, J., Alamgir, M., Cislowski, J. & Laurance, W.F. (2024). Ghost roads and the destruction of Asia-Pacific tropical forests. Nature, 629(8011), 370-375.

Engert, J.E., Souza Jr., C.M., Kleinschroth, F., Juffe Bignoli, D., Costa, S.C.P., Botelho Jr., J., Ishida, F.Y., Nursamsi, I. & Laurance, W.F. (2025). Explosive growth of secondary roads is linked to widespread tropical deforestation. Current Biology, https://doi.org/10.1016/j.cub.2025.02.017