Woody Plant Diversity and Community Structure Along Elevational and Soil Gradients in Betula platyphylla Forests,...

As a climate-sensitive region on a global scale, how environmental gradients on the Tibetan Plateau influence species diversity and community structure is an important scientific issue for understanding community assembly mechanisms in alpine ecosystems. This study focused on Betula platyphylla forests in the Nyang River Basin in the southeastern Tibetan Plateau (elevation 2990-4100 m), where a total of 16 plots (48 quadrats of 10 × 10 m) were established, field surveys were conducted, and hierarchical cluster analysis, canonical correspondence analysis (CCA), regression analysis, and Pearson correlation analysis were applied. The aims were to (1) explore the response patterns of woody plant diversity in B. platyphylla forests along the elevational gradient; and (2) evaluate the effects of key environmental factors, including elevation and soil properties, on the community distribution patterns of B. platyphylla forests. The results showed that a total of 71 woody plant species were recorded, belonging to 22 families and 40 genera, mainly represented by Rosaceae, Ericaceae, and Caprifoliaceae. It can be classified into four associations (Ass): B. platyphylla + Rhododendron bulu, B. platyphylla + Dasiphora fruticosa, Quercus aquifolioides + Lonicera tangutica, and B. platyphylla + Rhododendron triflorum. With increasing elevation, the species Margalef richness index (M), Shannon-Wiener diversity index (H), Patrick richness index (Pa), and Simpson diversity index (D) showed a significant decline (p < 0.05), while the Simpson dominance index (C) increased significantly (p < 0.05). The Pielou evenness index (J) did not significantly respond to elevational gradients (p > 0.05). CCA showed that environmental factors jointly explained 37.80% of the variation in community composition, among which elevation (Elev), soil alkali-hydrolyzable nitrogen (AN), organic matter (OM), and available phosphorus (AP) were the main environmental factors affecting the woody plant community composition of B. platyphylla forests (p < 0.05). This study provides key baseline data on plant diversity of B. platyphylla forests in this region and offers a scientific basis for the conservation and management of alpine forest ecosystems under climate change.