Identifying deforestation and defaunation fronts in Indonesia’s tropical forests

Dave James Ian Seaman, Maria Voigt, Nicolas J Deere, Nurul L Winarni, Sonny Mumbunan, Jatna Supriatna, Matthew J Struebig

Tropical forests are central to global climate regulation and biodiversity conservation, yet continue to face intense pressure from agricultural expansion, resource extraction, and infrastructure development. Indonesia contains some of the world’s largest remaining tropical forests and exceptionally high vertebrate diversity, but its islands differ widely in both historic forest loss and emerging development pressures. Here, we develop a spatially explicit, probabilistic modelling framework to map past forest-cover change (1990–2020) and project forecast deforestation risk to 2055 across Indonesia’s seven major island groups. We integrated these deforestation projections with species-specific Areas of Habitat for >3,000 terrestrial vertebrates to quantify spatial overlap between future forest loss and three biodiversity variables: species richness, range-size rarity, and extinction vulnerability. Model validation showed high predictive accuracy across all regions (92–98% pixel agreement), with deforestation strongly influenced by past forest loss, fire occurrence, peatland extent, and proximity to roads and plantations. Projections suggest continued but regionally uneven forest loss, with the greatest future declines expected in Sumatra, Java–Bali, and lowland Kalimantan, while Maluku and Papua are likely to retain most of their forest cover. Biodiversity–deforestation overlaps reveal acute defaunation fronts in northern Sumatra and western and central Kalimantan, where high vertebrate richness and extinction vulnerability coincide with intense projected forest loss. In contrast, the eastern archipelago contains large intact areas with high concentrations of range-restricted species but low deforestation risk, identifying proactive conservation priorities. Together, these findings highlight the urgent need for regionally differentiated strategies that curb biodiversity loss in active deforestation frontiers while safeguarding the globally significant intact forests of eastern Indonesia.