Fertility variation, defined as a difference in the ability to create progeny (i.e., reproductive success) among individuals, was reviewed using the related available theoretical and practical literature in an attempt to contribute to and improve future studies on the subject. Fertility variation is a useful guide for various purposes such as gene conservation, seed production programs, forest genetic resource (i.e., seed sources) management, other forestry practices (e.g., regeneration), and evolutional and physiological studies. Many papers and proceedings have been published, including both theoretical and practical approaches, on how fertility variation has improved in the last two decades. Large variations in fertility were widely reported among populations within species and among species. We reviewed the literature and combined our diverse knowledge to examine fertility variations and their linkage parameters. Fertility variations and their related parameters (e.g., gene diversity, status number, effective parent number, parental–balance curves) estimated based on reproductive characteristics have been studied for many years using easy and cheap surveys that are used for different purposes in forest sciences. Their importance is increasing and their use is becoming more widespread because of these advantages, leading to improvements in research papers. While many research papers have recently been published on fertility variations and linkage parameters, a review paper has not been published to date. Therefore, a review paper is needed based on a literature survey and unpublished experience, as a guide for future studies.

This research examines the impact of varied acorn yields on the effective population size of Turkey oak (Quercus cerris L.) as assessed through the fertility averages of zygotic parents. We selected two distinct populations from the species’ natural habitats based on their good and poor acorn production rates to investigate acorn production, growth attributes, and their interrelationships over three years of production and two years of growth data. Results showed that the population with good acorn production exhibited greater growth attributes and acorn yields compared to the poor acorn production population. Acorn production had lower coefficients of variation compared to growth attributes. Fertility variation in both populations was moderate, with a decrease in the effective number of parents from the population with abundant acorn production to the one with limited acorn production. The presence of mixed seeds from diverse populations had a detrimental impact on fertility variation and related metrics. Nonetheless, this study suggests that regions with limited acorn production still have the potential for natural regeneration due to their larger effective population size when coupled with appropriate forestry practices such as selective acorn harvesting to enhance genetic diversity. These findings emphasize the importance of accounting for fertility variation in the selection and management of seed sources, even within the context of a limited area and three years of data. Further research should be conducted in larger populations and over longer periods to draw more comprehensive conclusions.

Abies koreana E.H.Wilson (Korean fir), an endangered high-altitude conifer native to South Korea, is facing severe population decline due to climate change and low germination rates. While ecological factors have been studied, the genetic and epigenetic mechanisms underlying its seed development are still poorly understood. DNA methylation, regulated by MET1 and CMT2, plays a critical role in the stability of gene expression during seed development. This study investigates the expression patterns of MET1 and CMT2 across 12 developmental stages, from pre-germination to post-germination, with a focus on shoot and root tissues. RNA-seq data were analyzed to identify MET1 and CMT2, and expression patterns were validated using RT-qPCR. MET1 showed high sequence conservation with conifers such as Pinus sylvestris, indicating potential conservation of CG methylation mechanisms among conifer species. CMT2 showed lower sequence conservation across species, indicating reduced evolutionary conservation compared to MET1. Tissue-specific analysis showed MET1 being predominantly active in shoots during cotyledon development, while CMT2 was upregulated in roots at later stages. These findings highlight the dynamic and tissue-specific roles of DNA methylation in the seed development of A. koreana, contributing to a better understanding of the genetic and epigenetic mechanisms involved in its germination and early growth.