To understand the variation patterns of anatomical and functional traits in woody plants in along an altitudinal gradient in montane forests and to explore the mechanisms underlying the formation of vertical vegetation belts, this study examined 22 dominant broad-leaved tree species across four elevation levels (800, 1000, 1300 m, and 1700 m) in the Jinzhongshan Syrmaticus humiae National Nature Reserve, Guangxi. We measured wood density (WD), xylem hydraulically weighted vessel diameter (Dh), vessel density (VD), vessel wall thickness (T), vessel grouping index (Vg), the fraction of vessel (VF), axial parenchyma (APF), and fiber (FF). We calculated theoretical hydraulic conductivity (Kth), vulnerability index (VI), and vessel wall reinforcement coefficient (VWR). The analyzed focused on altitudinal trends in xylem anatomical structures, trait correlations across elevation gradients, and relationships between traits associated with water transport efficiency and safety. The results showed that: (1) With increasing altitude, tree wood traits tended to adjust vessel structures to resist xylem embolism, but at the cost of reduced hydraulic efficiency. Specifically, the average values of Dh, VD, and Kth across the four altitude gradients were 61.64 μm, 112.72 no mm?2, and 2.83 kg·m?1 MPa?1 s?1, respectively. Among these, both Dh and Kth gradually decreased with increasing altitude, while VD increased. (2) With increasing altitude, trees did not enhance mechanical strength by thickening vessel walls nor improve xylem cavitation resistance by increasing wood density. Mean xylem T and WD across the four altitudes were 2.71μm and 0.54 g cm?3, respectively, both declining with elevation. The mean vessel VI was 1.08, generally lower at higher than at lower altitudes. (3) Compared with global data, the xylem of the 34 tree species had a higher proportion of axial parenchyma, which reduced vessel embolism risk. (4) At each altitude gradient, no trade-off was detected between xylem hydraulic efficiency and safety. No significant correlations were found between Kth and VI, or between Kth and WD. However, Kth was significantly positively correlated with Dh (P < 0.05), and VI was significantly positively correlated with APF (P < 0.05). VD was significantly negatively correlated with both T and APF across the 4 altitude gradients (P < 0.05). These findings indicated that plants at low altitudes rely on larger vessels to improve water transport efficiency, while plants at high altitudes favor small vessel diameters to enhance xylem cavitation resistance. Insights from this study can inform tree species selection for subtropical mountain forest restoration under changing climate.