JEE Journal of Ecology and Environment RESEARCH Development of a habitat suitability index for the habitat restoration of Pedicularis hallaisanensis Hurusawa Rae-Ha Jang , Sunryoung Kim , Jin-Woo Jung , Jae-Hwa Tho , Seokwan Cheong , Young-Jun Yoon* Research Center for Endangered Species, National Institute of Ecology, Yeongyang 36531, Republic of Korea ARTICLE INFO Received September 29, 2022 Revised November 3, 2022 Accepted November 26, 2022 Published on December 21, 2022 *Corresponding author Young-Jun Yoon E-mail yjyoon@nie.re.kr Background: We developed a habitat suitability index (HSI) model for Pedicularis hallai- sanensis, a Grade II Endangered Species in South Korea. To determine the habitat variables, we conducted a literature review on P. hallaisanensis with a specific focus on the associat- ed spatial factors, climate, topography, threats, and soil factors to derive five environmental factors that influence P. hallaisanensis habitats. The specific variables were defined based on the collected data and consultations with experts in the field, with the validity of each variable tested through field studies. Results: Mt. Seorak had a suitable habitat area of 2.48 km 2 for sites with a score of 1 (0.62% of total area) and 0.01 km 2 for sites with a score of 0.9. Mt. Bangtae had a suitable habitat area of 0.03 km 2 for sites with a score of 1 (0.02% of total area) and 0 km 2 for sites with a score of 0.9. Mt. Gaya showed 0.13 km 2 of suitable habitat for sites with a score of 1 (0.17% of total area) and 0 km 2 for sites with a score of 0.9. Lastly, Mt. Halla showed 3.12 km 2 of suitable habitat related to sites with a score of 1 (2.04% of total area) and 4.08 km 2 of sites with a score of 0.9 (2.66% of total area). Mt. Halla accounts for 73.1% of the total core hab- itat area. Considering the climatic, soil, and forest conditions together with standardized collection sites, our results indicate that Mt. Halla should be viewed as a core habitat of P. hallaisanensis. Conclusions: The findings in this study provide useful data for the identification of core habitat areas and potential alternative habitats to prevent the extinction of the endan- gered species, P. hallaisanensis. Furthermore, the developed HSI model allows for the pre- diction of suitable habitats based on the ecological niche of a given species to identify its unique distribution and causal factors. Keywords: endangered species, endemic species, habitat restoration, habitat suitability index, Pedicularis hallaisanensis Introduction Pedicularis hallaisanensis Hurusawa, endemic species to South Korea, belongs to the genus Pedicularis L., within the Scrophulariaceae family. Approximately 600 species of Pedicularis are distributed in the polar regions of the northern hemisphere and alpine regions of the temperate zone (Yang et al. 1998). Eleven species of this semi-parasit- ic plant have been identified on the Korean peninsula, with five species, P. resupinata P. mandshurica , P. hallaisanensis , P. spicata , and P. ishidoyana , found in South Korea (Cho 2010). P. hallaisanensis was first discovered by Ichikawa in 1905 on Mt. Halla, Jeju Island, be called the two common names of the species, Halla-songipul and Seom-songipul in South Korea. Since 2012, the annual or perennial P. hallaisanensis has been designated as a Grade II Endangered Species for protection by the Ministry of Environment. The plants grow in full-sun locations on the rocky ridges of high-altitude mountains. The flowering period is from July to September and the distribution is considerably rare across the geo- graphical regions of Mt. Halla, Mt. Seorak, Mt. Bangtae, and Mt. Gaya (National Institute of Biological Resources [NIBR] 2018). Research on the genus Pedicularis in South Korea began with the first report on P. resupinata by Palibin (1900), fol- lowed by taxonomic studies by Nakai (1911), Jung (1956), Lee (1996a, b), as well as Cho and Choi (2011). Although P. hallaisanensis has been categorized as identical to P. spica- ta (Cho and Choi 2011), in our study, P. hallaisanensis and P. spicata are viewed as two distinct species owing to the lack of a comprehensive review with standardized collec- ISSN: 2288-1220 https://doi.org/10.5141/jee.22.067 (2022) 46:32 Copyright © 2022 The Author(s) Open Access This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. The publisher of this article is The Ecological Society of Korea in collaboration with The Korean Society of Limnology.