Zagarjav TsegmedP, Shukherdorj Baasanmunkh, Hyeok Jae Choi

Department of Biology and Microbiology, Changwon National University, Changwon, South Korea

Rheum nanum Siev. (Polygonaceae) is a perennial herbaceous plant distributed throughout cold desert regions of northern China, Kazakhstan, Mongolia, and the Altai Mountains of Russia at altitudes of 700–2000 m a.s.l. This species mostly distributed on rubble and rocky slopes of knolls north-facing hill slopes and nearly dry riverbeds and sandy-pebbly floors of valleys. Notably, the root of Rh. nanum is an essential portion of the diet of the critically endangered, restricted distribution Gobi bear (Ursus arctos gobiensis, Sokolov and Orlov), comprising roughly 30–35% of the entire autumnal diet. This study utilizes the MaxEnt model, along with field investigation data and online recorded data, selecting 249 effective occurrence points and integrating 23 environmental variables, such as bioclimatic and topographic, to evaluate the distribution patterns and dynamic changes of suitable habitats for Rh. nanum under current climatic conditions and four future climate scenarios (SSP126, SSP585). Results show that under current climatic conditions, the potential habitat of Rh. nanum spans approximately 504,163.9 km2, with high suitability areas concentrated in southern Mongolia. Key environmental factors influencing the species distribution include precipitation of warmest quarter (Bio18), annual mean temperature (Bio1), mean temperature of driest quarter (Bio9), temperature seasonality (standard deviation × 100) (Bio4), mean diurnal range (mean of monthly (max temp - min temp)) (Bio2), and elevation. In future climate scenarios, while the total suitable habitat area remains stable, the area of high suitability is significantly reduced. Specifically, under the SSP5-8.5 scenario, high suitability areas are projected to decrease by 27.84% during 2050. The centroid of high suitability areas is expected to shift northwestward, though a localized southeastward shift is observed under the SSP5-8.5 scenario. The conservation and protection of Rh. nanum resources, which is a key component of the forage of the Gobi bear (Ursus arctos gobiensis), will be greatly aided by this study, which is based on the current and future distribution predictions of Rh. nanum.