Elevated tree mortality as a regeneration niche for oak? Testing different management approaches in a meliorated floodplain forest

Abstract

Pedunculate Oak (Quercus robur L.), a keystone species in European temperate floodplain forests, faces regeneration challenges due to dense canopies caused by altered hydrology and declined traditional land-use practices. Recently increasing canopy mortality due to climate change altered forest structures and may offer new opportunities for oak regeneration. Over two years, including a drought year, this study examined the effects of higher and lower canopy mortality in combination with and without thinning of flood-intolerant species in the understorey compared to larger silvicultural cuttings (up to 0.72 ha) on the vitality and growth of planted Q. robur saplings in a meliorated floodplain forest in Leipzig, Germany. Canopy mortality alone did not improve the oak regeneration due to dark understorey conditions mainly created by fast-growing, flood-intolerant maple. However, combining high canopy mortality with species-selective understorey thinning markedly enhanced oak sapling growth and vitality. This management approach created higher light availability compared to unmanaged sites, but oaks expressed lower drought stress, indicated by δ¹ ³C in leaves, compared to larger cuttings. While greater canopy openness generally improved oak performance, its benefits were weakened by drought stress which was primarily correlated positively to vapour pressure deficit. The results demonstrate the potential of small-scale, selective thinning to support Q. robur regeneration under changing environmental conditions. Continued monitoring is essential to assess long-term outcomes, especially as oaks require increasing light with age. This study underscores the need for adaptive management complementary to hydrological revitalisation measures in floodplain forests to sustain biodiversity and associated ecosystem functions.