Decadal changes in population structures of rare oak species <i>Quercus chungii</i>

<i>Quercus chungii,</i> a rare and endangered endemic tree species, is found exclusively in subtropical regions of China. Understanding the population structure and temporal dynamics of <i>Q. chungii </i>is pivotal for effective conservation and restoration of its populations and associated ecosystems. However, large knowledge gaps remain about its population structure and temporal change, and its key demographic rates across size classes. In this study, we investigated the population structures of <i>Q. chungii</i> in 2013 and 2023 in a nature reserve specifically established to better conserve this species and its associated ecosystems. We found that <i>Q. chungii</i> increased in its overall abundance, and tree size in the past decade, suggesting active regeneration and a rapid growth rate for this species and the effectiveness of past conservation efforts. The age structure in 2023 showed a pyramid shape, with a sharp decline in the numbers of individuals from germinated seeds to seedlings and from seedlings to saplings. These led to the low numbers of seedlings and saplings and high age-specific death probabilities at the early developmental stages. These results indicated potential risks of future population decline. These risks may have already manifested over the past decade, as a high mortality rate during the seedling-to-sapling transition could be one of the primary reasons contributing to the decreased proportion of saplings in 2023 compared to 2013. We propose that future studies may benefit from in-depth studies on the regeneration processes of <i>Q. chungii </i>by considering seed predation and germination under changing climate. This study improves the prediction of population development of <i>Q. chungii</i>, thereby offering theoretical guidance essential for its conservation.

陈氏栎（Quercus chungii）是一种珍稀濒危的特有树种，仅分布于中国亚热带地区。明晰该物种种群结构与时间动态特征，对其种群及关联生态系统的有效保护与修复至关重要。然而，目前学界对其种群结构、时间变化规律，以及不同径级下的关键种群生命率仍存在大量认知空白。本研究于2013年与2023年，在专为保护该物种及其关联生态系统而设立的自然保护区内，对陈氏栎的种群结构展开调查。研究发现，近十年来该物种的总体个体数量与林木径级均有所提升，这表明其正处于活跃更新状态且生长速率较快，同时也印证了此前保护工作的成效。2023年的年龄结构呈金字塔形，但从萌发种子至幼苗、幼苗至幼树的个体数量均出现急剧下降，导致早期发育阶段的幼苗与幼树数量匮乏，且该阶段的特定年龄死亡率较高。上述结果预示了该种群未来可能出现衰退的潜在风险。这类风险或已在近十年间显现——幼苗向幼树过渡阶段的高死亡率，可能是2023年幼树占比相较于2013年有所下降的主要原因之一。我们建议，未来研究可结合气候变化背景下的种子捕食与萌发过程，对该物种的更新机制展开深入探究。本研究提升了对陈氏栎种群发展的预测能力，可为其保护工作提供不可或缺的理论指导。