Camera-trapping reveals both defaunation and conservation priority species in an unprotected forest in Vietnam

The ongoing decline of global biodiversity has prompted calls for an increase in protected area coverage. However, decisions on where to expand protected areas for optimal conservation impact are often hampered by an incomplete knowledge of biodiversity, especially in the tropics. In Vietnam, many unprotected forest areas have never had standardized biodiversity surveys, and much remains unknown about the status of conservation-priority species in these areas. We conducted systematic landscape-scale camera-trapping in an unprotected forest in central Vietnam with the goal of assessing the status and distribution of ground-dwelling mammal and bird communities, especially threatened and Annamite endemic species. We analyzed occurrence data within an occupancy framework to further characterize these communities and establish a baseline for potential long-term monitoring. We also assessed the completeness of the mammal and bird communities compared to historical reference communities using a defaunation index. In total, we recorded 21 terrestrial mammals and birds over 6156 camera-trap days, including one Annamite endemic and six species listed as threatened on The IUCN Red List of Threatened Species. We included 16 mammals and birds in the occupancy models, which showed high heterogeneity in both occupancy and detection estimates, with predicted occupancy for one priority species (Annamite striped rabbit) comparable to one other protected area in the region. However, despite the presence of several conservation priority species, the forest area has undergone high levels of defaunation, as evidenced by the failure to record 55 % of the historical faunal community. The historical defaunation index values showed the highest values for the carnivore guild, and for large (>100 kg) species. We discuss our findings within the context of the importance of this area for the protection of conservation-priority species and potential future gazettement, and the usefulness of systematic landscape-scale surveys to fully assess biodiversity in forested regions that are outside the protected area system in Vietnam and beyond.