Trans-Purus: Brazil's last intact Amazon forest at immediate risk (commentary)

[Judi Lynn]

Commentary by Philip M. Fearnside; Lucas Ferrante; Aurora M. Yanai; and Marcos Antonio Isaac Júnior on 24 November 2020

Brazil’s remaining Amazon forest is roughly divided in half by the Purus River, just west of the notorious BR-319 (Manaus-Porto Velho) highway. To the west of the river lies the vast “Trans-Purus” region — intact rainforest stretching to the Peruvian border. To the east, the forest is already heavily deforested, degraded and fragmented.

Multiple threats are now closing in on the Trans-Purus region, and expected to increase greatly with the impending “reconstruction” of the BR-319. Planned roads linked to the BR-319 would open the Trans-Purus region to land grabbers (grileiros), organized landless farmers (sem-terras) and other actors from Brazil’s “arc of deforestation.”

A massive planned gas and oil project would also likely lead to new road connections to the other planned highways in the Trans-Purus area, opening even more of the region to invasion. Asian oil palm and logging companies are among those with a historical interest in the area.

This last large block of intact Brazilian Amazon forest is essential for ecosystem services — maintaining biodiversity, carbon stocks, and the forest water cycling functions essential for rainfall in other parts of Brazil and neighboring countries. This post is a commentary. The views expressed are those of the authors, not necessarily Mongabay.

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 species would be threatened by 2050 depends heavily on the large block of forest west of the Purus River remaining intact. Importantly, this block of forest remains intact in the deforestation scenario used by Gomes and collaborators because it is based on the projection of the model by Soares-Filho and collaborators (Figure 1). This deforestation simulation did not consider the roads planned in the Trans-Purus region that would open this vast block of forest for the entry of deforesters.

More:
https://news.mongabay.com/2020/11/trans-purus-brazils-last-intact-amazon-forest-at-immediate-risk-commentary/