4.2 Changes in the Potential Geographical Distribution of T. sinense
Our investigation revealed fluctuations in the total suitable area ofT. sinense , which decreased from 758,258 km2 to 731,469.3 km2 from the last interglacial period to the last glacial maximum. During this period, suitable habitat contracted, primarily concentrating in the central part of southwest China. The mountainous terrain in this region acted as a barrier against cold air, mitigating extreme climate fluctuations and providing stable conditions conducive to species survival (Stewart et al., 2010; Li, 2017). Furthermore, the absence of geographical barriers facilitated migration to this area, establishing Southwest China as a critical refuge for the Tertiary relict T. sinense (Chen et al., 2011; Liang, 2020) . Subsequently, from the last glacial maximum to the mid-Holocene, the total suitable area expanded to 750,132.8 km2, with suitable habitat extending outward from the Sichuan Basin and Yunnan-Guizhou Plateau. This expansion correlates with the warmer and wetter global climate during the mid-Holocene, aligning with the hydrothermal conditions favorable for T. sinense growth. Consequently, the population of T. sinense exhibited significant glacial contraction and post-glacial expansion, consistent with findings for other species such as Thuja sutchuenensis (Qin et al., 2017) ,Davidia involucrate (Ye et al., 2021) , and Ulmus elongate (Zhang et al., 2021) .
In the future, global climate warming is anticipated to substantially impact suitable habitats for T. sinense , resulting in a significant distribution shift. The extent of this shift varies depending on emission scenarios, with the largest loss area observed in the SSPs8.5 scenario and the smallest in the SSPs2.6 scenario. This disparity is attributed to temperature surpassing the threshold required for optimal T. sinense growth in the SSPs8.5 scenario. Consequently, temperature increase emerges as a primary driver of future reductions in suitable distribution areas. Extensive research underscores the transformative effect of climate change on species distribution, often leading to migration towards higher latitudes (Thuiller, 2003; Chen et al., 2011). Consistent with this trend, our study forecasts a shift in T. sinense ’s suitable habitats to higher latitudes under future climate scenarios. These observations suggest that previously unsuitable high-latitude regions may become conducive to T. sinense survival as global temperatures rise, making them preferred areas for ex situ conservation efforts. Overall, the dynamic response of T. sinense ’s geographical distribution to climate fluctuations underscores its adaptive capacity to climate change, highlighting the necessity for strategic conservation measures.