As the small plane's engines roar, the far-below patchwork of cattle ranches, farms and roads set amid fragments of Amazon rainforest gradually give way to an unbroken expanse of pristine jungle extending to the horizon in southeast Colombia.

This rare undisturbed forest, stretching across three provinces, is an indigenous sanctuary, a key repository for vanishing plants and animals, and a crucial natural buffer against rising climate change risks.

But the mining, ranching and logging threats devastating large areas of the Amazon basin are creeping toward this isolated corner of Colombia, and anxieties are growing.