Opposite Tree-Tree Interactions Jointly Drive the Natural Fir Treeline Population on the Southeastern Tibetan Plateau

The long-term stability of alpine treeline positions and increased stem density are frequently reported by recent studies; however, whether a denser forest is relevant to competitive tree–tree interactions remain unclear. Herein, we mapped surveyed individual trees in two undisturbed Smith fir (Abies georgei var. smithii) plots (with size: 30 m × 200 m; plot NE1: 4477 m, NE2: 4451 m) near Ranwu Lake (RW) on the southeastern Tibetan Plateau. surface pattern method spatial point analysis were used detect distribution patterns three size classes (seedlings, juveniles, adults) associations between pairwise classes. We also compared our results five other forests (Deqin, Linzhi, Changdu, Yushu, Aba) from Young dominated plots. Both positive negative autocorrelations for all detected study Intraspecific facilitation competition coexisted at treelines regions (RW, characterized mild moist climate, whereas intraspecific (Changdu, Deqin, Yushu), which featured seasonal climatic stress or high disturbance pressure. Thus, can be linked relatively favorable environmental conditions. Overall, population mainly shaped combination thermal moisture conditions modulated non-climatic variables (e.g., history microtopography).