A flexible tool to prioritize areas for conservation combining landscape units, measures of biodiversity, and threats

Expanding the reserve system is a key strategy to enhance biodiversity protection. Yet, conservation outcomes can be undermined by underrepresentation of some habitats and opportunistic placement of protected areas. Irreplaceability and vulnerability, the key principles of conservation, should thus be combined within a bioregionalization framework to implement protection in the habitats that most need it. We proposed a simple and flexible method to prioritize bioregions for conservation based on these principles and used it to rank the 85 bioregions of the Australian continent. To do so, we quantified biodiversity values and threats in each bioregion by gathering open-access data on species, landscapes, and land use. Bioregions were then ranked using a set of customizable scenarios, including ecologically meaningful combinations of measures of irreplaceability and vulnerability. To identify biodiverse areas under threat but potentially overlooked, we compared our results with the location of already established biodiversity hotspots (i.e., areas identified as important for biodiversity and under threat). We found that bioregions with the highest biodiversity values are predominantly located in the southwest, east, and north of the continent. Similarly, threats, particularly land clearance, are concentrated along the east coast and in the southwest. When ranking bioregions using scenarios including both threats and biodiversity values, the majority (75%) of the highest-ranking bioregions were already included in biodiversity hotspots. For five of these bioregions, the proportion of protected land to date still falls below the 17% recommended by the Convention on Biological Diversity and thus they likely require prompt prioritization and intervention. The method proposed can support ongoing monitoring and prioritization of land units for conservation. Its simplicity and flexibility mean it can be easily adopted for different areas and adjusted to local priorities.