Gene–environment interactions govern early regeneration in fir and beech: evidence from participatory provenance trials across Europe

Summary Forest regeneration is shaped by strong demographic filters during germination and early establishment, yet the relative contributions of provenance and environment remain poorly resolved under natural conditions. We combined climate-chamber trials with a continental-scale, field-based citizen science seed-sowing experiment to quantify germination, early phenological development, and three-year post-germination survival fir (Abies spp.) and beech (Fagus spp.) provenances across Europe. Using mixed-effects models and a state-based Markov framework to reconstruct phenological trajectories, we quantified successive demographic filters from seed to established seedling. Germination was structured by genotype-by-environment interactions (G × E) in both genera, but with contrasting expression: fir showed broadly parallel environmental responses among provenances and partial concordance between climate-chamber and field, whereas beech showed strong provenance-by-environment responses and weak predictability from controlled conditions. Seed weight was a key axis in beech (lighter seeds germinated more and developed faster), but confounded with geographic differentiation in fir. In contrast to germination, post-establishment survival was dominated by site-level environmental filtering with limited consistent provenance effects, revealing a life-stage shift from fine-scale G × E during germination and early development to broader environmental control of survival—an important consideration for regeneration—based management and assisted migration. Competing Interest Statement The authors have declared no competing interest. Footnotes ↵** Shared senior authorship https://github.com/kcsillery/MyGardenOfTrees_PilotTrials/tree/main