Seed Quantity and Quality Variation in European Beech ( Fagus sylvatica L.): A Comparative Analysis of Different Crop Years

European beech ( Fagus sylvatica L.) is characterized by inter -annual cycles of seed production (masting), with synchronized high seed production between sites in some years. The importance of both seed quantity and quality monitoring stems from its role in sustaining the ecological balance, promoting biodiversity, and ensuring the long-term viability of forest ecosystems. This study aimed to (1) describe seed production from 2015 to 2022, (2) identify the potential factors that could affect the yield appearance and seed quantity, and (3) compare the quality of beechnuts from different crop years in Croatia. At each of the six forest seed objects located in the area of forest administrations Bjelovar, Karlovac, Ogulin, Po & zcaron;ega, and Delnice, we selected 5 trees for seed collection. Seeds were collected with large PVC nets covering total projection area of the tree crowns. Seed quality testing was performed according to the International Rules for Seed Testing (ISTA Rules). Our results indicate a consistent biennial beechnut cycle. The crop was completely absent in 2015, 2017, 2019 and 2020, while 2016, 2018, 2020 and 2022 were fruitful years. Weather plays a key role in triggering masting. We found that beechnut production is influenced by summer weather conditions (from June to August) in the previous two years. Abundance of beechnut production varies on an annual level, population level and on individual trees. Factors that partially explain the variability in yield are tree height and crown size. No significant differences in viability were found across different years and sites, though the results should be approached with caution due to limited sample representation. The study identified a positive correlation between seed weight and viability, as well as the impact of precipitation on moisture content. The results emphasize the need for continued monitoring and further research to understand the factors influencing beechnut production and quality, crucial for sustainable forest management in the face of climate change.