Altitudinal effects on intra-annual xylem formation characteristics and environmental response in Picea crassifolia on the northeastern Tibetan Plateau - Le Zhang; Liang Jiao; Peng Zhang; Xuge Wang; Saipeng Hou; Yuanyuan Ma; Yarong Qin; Kuan Zhang; Zhengdong Guo (Forest Ecology and Management, 2026)