Conserving Southeast Asian trees requires mitigating both climate and land-use change

The forests of Southeast Asia harbour high levels of species diversity, providing a plethora of ecosystem services. However, this biodiversity is threatened by both climate and land-use change, the impacts of which are poorly understood. We modelled 1,498 tree species distributions under four shared socioeconomic pathways (SSPs) with varying global change intensities, and classified species into 11 spatially associated groups. We found both global changes to cause severe losses in tree distributions. Only under SSP1–2.6, the sustainable pathway with low intensities in both global changes, were distribution losses mitigated. Unexpectedly, losses were overall greatest under intermediate climate change pathways SSP2–4.5 and SSP3–7.0 rather than under the most extreme pathway, SSP5–8.5. This was because, although climate-driven losses were greatest under SSP5–8.5, land-use-driven losses were much more extensive under SSP2–4.5 and SSP3–7.0 than under SSP5–8.5. Crucially, other than SSP1–2.6, each SSP led to worst-case scenarios for several species groups. Our findings highlight that to most effectively conserve Southeast Asian tree distributions, policymakers need to prioritize a sustainable pathway that mitigates both global changes.