While the high elevation limit of trees is commonly related to low temperature, the rear edge of their distribution is often associated with drought. Here we explore phenology traits that contribute to a mechanistic explanation of both these edges of the fundamental niche in the broad leaved evergreen Quercus pannosa s.l. Populations of this species reach a drought limit (DL) at 2510 m in the semi-arid upper Yangtze valley, and a cold limit (CL) at 4270 m, very close to the conifer treeline, within a short geographical distance. Trees reach a height of only 4–7 m at both climatic limits, and > 30 m height at optimum site (OS) at 3440 m. At OS, flushing starts in mid-May and at the summer solstice at CL (after late frosts end), suggesting a photoperiod control. At DL, oak phenology tracks the (irregular) arrival of the monsoon. Shoots and leaves grew fastest and for the shortest period at DL, and slowest at CL, in both cases forming 4–7 cm long new shoots per year, contrasted by 12–13 cm a⁻¹ at OS. Maturation of leaves (length and specific leaf area, SLA) was again fastest at DL, followed by CL and slowest at OS, with a much longer shoot growth duration per year and bigger leaves. We conclude that the period favorable for growth and maturation was more than halved at both range limits (by frost or drought) compared to the optimum site, pointing at a common range restriction by the duration of the growing season.

虽然树木的高海拔极限通常与低温有关，但其分布的后缘通常与干旱有关。在这里，我们探索物候性状，有助于对阔叶常绿阔叶栎（Quercus pannosa）基本生态位的两个边缘进行机械解释。sl该物种的种群在半干旱的长江上游流域在2510 m处达到干旱极限（DL），在很短的地理距离内非常接近针叶树林的寒冷极限（CL）达到4270 m。在两个气候极限下，树木的高度都只有4–7 m，而在3440 m的最佳站点（OS）处，树木的高度超过30 m。在OS中，冲洗从5月中旬开始，在CL的夏至开始（霜冻后期结束后），这表明应进行光周期控制。在DL，橡树物候学跟踪季风的（不规则）到达。在DL上，枝条和叶子生长最快，最短，而在CL上最慢，这两种情况下每年形成4–7 cm长的新芽，而a ^-1则为12–13 cm在OS。叶片的成熟度（长度和特定叶面积，SLA）在DL上再次最快，其次是CL，在OS上最慢，每年的芽生长期更长，叶子更大。我们得出的结论是，与最佳位置相比，在两个范围限制（受霜冻或干旱）的影响下，有利于生长和成熟的时期减少了一半以上，这表明生长季节持续时间限制了范围。