The text of this commentary is updated from an earlier Portuguese-language version of the first author’s column at Amazônia Real. Why is the Trans-Purus region important? The Brazilian Amazon is divided between its eastern side, where the forest is heavily deforested and fragmented, and the western side (west of the Purus River, in Amazonas state), where the forest is largely intact due to the lack of accessibility by road. But this situation in the western part of the Amazon is about to change radically due to a series of roadbuilding threats. The impacts would be enormous if a new frontier in this “Trans-Purus” region is opened to the migration of actors and processes already at work in the “Amazon arc of deforestation” (the area along the southern and eastern edges of the Amazon rainforest where deforestation has historically been concentrated). The Trans-Purus region is key to maintaining Amazon biodiversity, as shown by a 2018 study published in the journal Nature Climate Change by Vitor Gomes and collaborators. This much-needed analysis of the combined effect of projected deforestation and climate change on Amazonian biodiversity arrived at a bleak conclusion: 49.6% of the 6,394 tree species with reliable data would be threatened by 2050, according to Criteria A4, B1 and D2 of the International Union for the Conservation of Nature and Natural Resources (IUCN). New threats to the Trans-Purus region make this Amazon outlook even more dire than that shown by the Gomes study. The discovery that (only) half of the tree…This article was originally published on Mongabay Läs mer