Re-visiting the ancient forest: the analysis of basal area increment reveals the present oak old growth of the Białowieża forest interior recruited amongst pioneering trees

Abstract Tree-ring analysis provides a powerful tool for reconstructing past environmental and ecological conditions. This study examines the early growth dynamics of pedunculate oak ( Quercus robur ) and sessile oak ( Q. petraea ) across 30 stands in Eastern Europe, including the Białowieża National Park (BNP), by analyzing their basal area increment (BAI) over the first 55 years of growth. We identified three distinct BAI models reflecting different early-life growth trajectories, potentially indicative of varying habitat characteristics during the recruitment phase. While these models were present across the geographically diverse study area, their relative frequencies varied significantly between individual stands, indicating a strong influence of local ecological contexts on early oak development. Notably, the majority of oaks within the BNP exhibited a slow and steady linear BAI increase. This homogeneity infers a consistent, yet suboptimal, growth environment within the BNP interior during this period. We suggest that this growth pattern is indicative of oak regeneration occurring predominantly under the translucent canopies of pioneering tree species that established following historical disturbances. This finding contrasts with the heterogeneous BAI patterns observed in semi-open stands and wood pastures, highlighting the distinct ecological history of oak recruitment within the BNP’s forest interior. Our results challenge the notion that the current oak old-growth in BNP is primarily a direct legacy of extensive, long-lasting semi-open silvopastoral woodlands conducive to rapid early oak growth. Instead, they support a model of oak establishment within a dynamic forest shaped by specific anthropogenic historical disturbances followed by spontaneous ecological succession.