Pinus koraiensis Siebold & Zucc. (Korean pine) is a key species of the mixed cold temperate forests of Northeast Asia. Current climate change can significantly worsen the quality of P. koraiensis habitats and therefore lead to a large-scale structural and functional transformation of the East Asian mixed forests. We built a species distribution model (SDM) for P. koraiensis using the random forest classifier – a versatile machine learning algorithm, to discover overlap areas of potential species occurrence in the climate condition of the Last Glacial Maximum (~21,000 year before present) and in the projected future climates (2070 year), from which possible permanent refugia for P. koraiensis were identified.

Using the random forest supervised learning algorithm, we developed models of the modern distribution of P. koraiensis in accordance with the five selected bioclimatic variables (Kira's warmth and coldness indices, the index of continentality, the rain precipitation index, and the snow precipitation index). In addition to current climatic conditions, we performed this analysis for the climate of the Last Glacial Maximum and for the future projected climate (2070) under scenarios RCP2.6 and RCP8.5. Among the predictors, the rain index appears to be the most significant. The land area estimates with high suitability for P. koraiensis was 303,785 ​km² under current climatic conditions, 586,499 ​km² for the Last Glacial Maximum, and 337,573 ​km² for the future (2070) period under the RCP2.6 scenario, and 397,764 ​km² under the RCP8.5 scenario.

Most of the potential range of P. koraiensis during the Last Glacial Maximum was located outside the current distribution area of the species. The climatically suitable P. koraiensis habitats will likely disappear in the western part of its modern range. In the southern part of the range, which includes glacial refugia, the areas of continuous distribution of the P. koraiensis populations since the end of the Pleistocene are expected to be fragmented, but some localities in the north of the Korean Peninsula, northeast China, southern Primorye (Russia), and central Honshu (Japan) with suitable climatic conditions for the species will support the existence of populations.