4.1 Environmental Factors Affecting T. sinense Distribution
Results from the jackknife test and analysis of the main parameter table underscore that the potential distribution of T. sinense is influenced by four key environmental factors: Bio4, Bio6, T_CACO3, and Elevation. Elevation plays a significant role in species distribution by indirectly affecting temperature and precipitation (Clark et al., 2007; Ma et al., 2021). While topsoil calcium carbonate does impose some restriction on plant distribution, its impact appears less pronounced (Wang et al., 2023). Therefore, temperature emerges as the primary factor shaping the geographical distribution of T. sinense , a finding corroborated by previous studies. Li (2021), for instance, employed the concept of space-time substitution to investigate the influence of altitude on the reproductive characteristics of T. sinense , proposing that temperature variations impact species fitness and could prompt migration to higher altitudes with rising temperatures. Similarly, Chen et al. (2023) through correlation analysis of chronological and meteorological factors, identified air temperature during specific periods as a key influencer during T. sinense growth stages.
The permutation importance (PI) and jackknife tests further highlight the critical role of the minimum temperature of the coldest month (bio6) in shaping the potential geographical distribution of T. sinense . This finding aligns with observations in other species such asQuercus mongolica (Yin et al., 2013) , Santalum album (Hu et al., 2014) , Gymnocarpos przewalskii (Zhao et al.,2020) , andThuja sutchuenensis (Ma et al., 2021) . Chen’s research also revealed a significant negative correlation between T. sinense growth and the lowest temperatures in November. Consequently, the minimum temperature during the coldest month emerges as a pivotal factor constraining northward expansion of T. sinense . Low temperatures not only hinder seed germination and morphological development but also pose challenges to the species’ cold resistance, ultimately impeding its normal growth and development in northern China.