Provenance and environment jointly shape early regeneration in fir and beech: evidence from distributed participatory trials across Europe

Summary Forest regeneration is shaped by strong demographic filters during germination and early establishment, yet the relative contributions of seed provenance and environment remain poorly understood 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 3‐yr postgermination survival of fir ( Abies spp.) and beech ( Fagus spp.) provenances across Europe. We estimated germination metrics, reconstructed phenological trajectories, and quantified successive demographic filters from seed to established seedling. Germination was structured by provenance‐by‐environment interactions in both genera, but with contrasting expression. Fir showed broadly parallel environmental responses among provenances and partial concordance between climate‐chamber and field results, whereas beech exhibited strong provenance‐by‐environment responses and weak predictability from controlled conditions. Seed weight was a key axis of variation in beech (lighter seeds germinated more frequently and developed faster), but its effects in fir were confounded with geographic differentiation. Post‐establishment survival was dominated by site‐level environmental filtering and site‐by‐provenance interactions, with limited consistent provenance effects. This reveals a life‐stage shift from fine‐scale provenance‐by‐environment effects during germination and early development to broader environmental control of survival – an important consideration for regeneration‐based management and assisted migration.