Integrating dark diversity perspective into species conservation: A novel regional species protection index (RSPI) for identifying priority areas

• A novel application of dark diversity in plant conservation enhances plant extinction risk assessment and prioritization. • A Regional Species Protection Index (RSPI) was constructed by incorporating Dark diversity and species conservation value. • RSPI effectively identifies high conservation priorities areas and supports the protection of endangered species. • Addressing gaps between the RSPI and National Park boundaries supports endangered species spatial conservation planning. Understanding the spatial extinction risk of plants and identifying areas with high conservation priority are crucial for large-scale biodiversity conservation and protected area planning. However, research on plant extinction risk from the perspective of dark diversity has been largely neglected, and the combination of endangered species conservation value and dark diversity has rarely been incorporated into plant conservation planning. To fill this gap, this study introduced a new index, the Regional Species Protection Index (RSPI), to assess plant conservation priority areas. The results showed that: (1) The average probability of dark diversity in the Three Rivers Headwaters Region (TRHR) is 0.74, 1,830 species were considered to belong to the dark diversity species collection, and plants in the eastern and southeastern regions faced certain extinct risks; (2) RSPI was able to effectively capture the spatial distribution pattern of extinction risk, 32 % showed high conservation priority, accounting for 16,452.35 km 2 of TRHR. Compared with other conservation value assessment indices, RSPI highlights the importance of incorporating high extinction risk and endangered species conservation values into the species diversity conservation framework. (3) By comparing RSPI with the spatial boundaries of the TRHR Nature Reserve and National Park, approximately 25 % of high conservation priority areas and 50 % of medium conservation priority areas were not included in the conservation. This study innovatively combined dark diversity with endangered species conservation value, providing a new perspective for plant species conservation in alpine ecological zones and providing technical support for optimizing the management zoning of similar protected areas and national parks.