Variability of seed germination and early grown seedling traits across different seed origins of Chestnut-leaved Oak (Quercus castaneifolia CA Mey.) in Hyrcanian forests

Background and Objectives: An important portion of the failure observed in Chestnut-leaved oak afforestation programs is related to the geographic origin of seeds and seedlings and its influence on establishment and growth of seedlings. The lack of provenance-based evaluations for determining appropriate seed and seedling transfer zones, as well as the effects of mother trees on seedlings establishment and early growth in local nurseries and plantation sites, which are directly linked to climate change adaptation, is quite remarkable. Therefore, the present study aimed to investigate the variability of seed germination traits and early growth characteristics of Chestnut-leaved oak seedlings in different seed sources of Hyrcanian forests.
Materials and Methods: Acorns were collected from 3 Hyrcanian forest sites (Asalem in Guilan, Neka in Mazandaran, and Loveh in Golestan), each representing 3 elevational gradients (lowland, midland and highland). Acorns were then sown at the Pasand Forest and Rangeland Research Station. Totally seeds from 9 provenances and 90 mother trees (10 per provenance) were evaluated under a nested experimental design for germination performance and early seedling growth. Germination traits including germination percent, mean germination time, germination rate, radicle and plumule length, their biomass and ratio were measured. Experimental data were analyzed using a uni variate nested ANOVA. Treatment means and their effects were compared using Student Newman Keuls (SNK) multiple range test at 5% significance level.
Results: The results indicated that seed provenance and maternal trees had significant and broad effects on all germination traits, growth indices, and biomass of Oak seedlings. The highest germination percentage (89.8%), germination rate (0.57 seed.day⁻¹), and seed vigor index (18.78) were observed in the higher elevation provenance seed lot of Golestan Province. In contrast, the growth characteristics of seedlings, including shoot length, stem diameter, and dry weight of different parts of seedlings were greatest in the forest sites of Guilan Province, particularly in the lowland and mid-elevation zones. Seedlings originating from Loveh Forest (Golestan) exhibited greater root length and higher root-to-shoot ratios, reflecting an adaptive strategy of this population to warmer and drier conditions. Correlation analysis revealed that site-related factors such as elevation, slope aspect, canopy cover, and heat load index (HLI) were significantly associated with several germination traits and early growth parameters of Chestnut-leaved oak seedlings.
Conclusion: Overall, the findings demonstrated that the harsher the environmental and site conditions of the maternal seed provenance, the higher the germination-related indices of its seeds, and the more favorable the early growth performance of the resulting seedlings. This suggests that seedling producers can benefit from using seeds originating from such environments. In this study, the high-elevation sites of Golestan particularly the Loveh Forest provided the strongest seed sources, indicating that this area is highly suitable for collecting Oak seeds for seedling production within the Hyrcanian region.
In general, the results showed that one source of Chestnut-leaved oak seeds cannot be absolutely recommended as the best source in Hyrcanian forests and the decision on the best provenance of acorns can depend on the objectives of the project. Therefore, it is recommended to use acorns from Golestan province in cases where rapid establishment and high seed germination rate are desired, but in cases where faster increase in seedling height and higher growth potential of seedlings' aerial parts are more desired in the nursery or the planting area, the use of seeds from Guilan origin, especially in mid- and low-altitude areas, should be given priority. However, given the significant variability in germination and vegetative traits of seedlings in different mother trees, it is advisable to conduct additional studies in this field to collect and transfer Chestnut-leaved oak acorns in Hyrcanian forests.