1. INTRODUCTION
Population structure and its dynamics are fundamental to understand and predict population development and critical for the conservation of rare and endangered species (Harcombe 1987, Ezard et al. 2010, Salguero-Gomez and Gamelon 2021). Quercus chungii is a tree species of Fagaceae, endemic to China, and rare and endangered in Fujian Province (Wang et al. 2011, Jiang et al. 2019, Sun et al. 2021). The distribution area and population size of Q. chungii drastically reduced in the last century due to extensive logging for its high-quality timber (Wang et al. 2011). Previous work has focused on the community structures ofQ. chungii forest communities, and spatial genetic pattern and distribution, seed production and germination of Q. chungii population (Chen 2004, Huang et al. 2010, Li et al. 2010, Wang et al. 2011, Huang et al. 2017, Jiang et al. 2019, Sun et al. 2021). However, large knowledge gaps remain about its age or size structures and temporal change, and its key demographic rates across age classes. Understanding the population structure and its temporal dynamics ofQ. chungii is crucial for conserving and restoring Q. chungii population and its associated communities and ecosystems.
Age structure and life table are important tools to study population demographics (Harcombe 1987, Ezard et al. 2010, Jones 2021). We can infer reproductive strategy and predict population development from age structure by presenting the number of individuals in different developmental stages of a population. The information of age structure can be further used to construct a life table by calculating the key population parameters, such as age-specific survival and mortality probabilities. Thus, life table is a fundamental tool to explore the heterogeneity of demographic processes across population developmental stages and predict population dynamics and structures (Harcombe 1987, Jones 2021). Static or period life table is often used for long-lived species as it is difficult to track individuals from birth to death for such species (Jones 2021). It focuses on the fate of a population with mixed age classes during a particular time period. We can derive survivorship and mortality curves (Harcombe 1987) from life tables to assess mortality risks across age classes. There are usually three types of survivorship curves. Type I is a convex curve, indicating an increasing risk of death with age. Type II is a declining line, indicating a constant risk of death over all ages. Type III is a concave curve, indicating a decreasing risk of death with age. Survivorship curves of long-lived, slowing-growing tree populations may not exactly fall into the three above types, but show a mix of them (Harcombe 1987).
Seeds are essential for population survival and development, as they determine seed plant reproduction and represent the start of any seed plants ( Willson al. 2014). Although seed data are crucial for population analyses of plant species (Adams et al. 2005, Salguero-Gomez and Gamelon 2021), they are rarely incorporated into life table analyses of tree populations. Since seed data are usually difficult to obtain, most previous studies on tree population life tables set seedlings or sapling as the starting stage (Farahat 2020, Wei et al. 2020, Ta et al. 2021, Wu et al. 2021, Zhang et al. 2023). Ignoring seed stage may result in inaccurate assessment and prediction of population demographics.
This study focuses on the population structure and its temporal change of Q. chungii in the Fujian Minqing Huangchulin National Nature Reserve, which was established in 1985 to better conserve Q. chungii and its associated communities and ecosystems (Li et al. 2010). We aim to study the following questions: (1) What is the current population structure of Q. chungii ? (2) How do the population structures change from 2013 to 2023? (3) How does the mortality risk change across size classes? We surveyed population of Q. chungii in both 2013 and 2023, and compared their temporal changes in population structures. We estimated the number of germinated seeds from a previous study on seed rain of Q. chungii . We assessed the mortality risks across size classes by deriving survivorship and mortality curves from the static life table. This study would improve the understanding of current status and the prediction of the future development of Q. chungii population, thus providing important guidance for the conservation of Q. chungii .