Oaks under continuous cover forestry : recruitment challenges and biodiversity implications

Oak forests provide essential ecosystem services and support a disproportionate share of forest biodiversity in temperate regions, yet their long-term persistence is increasingly limited by insufficient recruitment. Although regeneration failure is well documented, comparatively little is known about growth of oak recruits in intermediate size classes (dbh 5–20 cm), particularly near the northern distribution limit. Continuous cover forestry (CCF) is increasingly promoted as a management approach to reconcile timber production, biodiversity conservation, and climate adaptation, with selective cutting as a management tool. This thesis investigated how selective cutting, stand structure, and climate affect oak recruitment and oakassociated biodiversity by combining long-term observational data from the Swedish National Forest Inventory with field experiments across southern Sweden. Across studies, oak recruitment was consistently constrained by competitive stand conditions, particularly high stand basal area, stem density, and proportions of shade-tolerant species. Selective cutting showed no short-term effect on oak recruit density but was associated with increased diameter growth of oak recruits after a sixteen-year period. Selective cutting also supported epiphytic lichen species richness and evenness, while unmanaged stands showed declines, although foliose lichens decreased across treatments which could not be fully explained. Long-term inventory data further revealed a pronounced decline in growth of oak recruits over the past four decades that persisted even after accounting for stand structure, site conditions, and climatic variability. Overall, our results show that successful oak recruitment under CCF requires balancing continuous forest cover with sufficiently strong or repeated interventions to reduce competition and maintain light availability. Integrating recruitment objectives with biodiversity goals is therefore essential to ensure the long-term persistence of oak-dominated forests under ongoing climate change.