Conspecific density enhances sound seed production during high-seed years in European beech

Katarzyna Kondrat, Jakub Szymkowiak, Maciej K. Barczyk , Urszula Eichert, Patrycja Jerzyńska, Maria Bogdańska, Jessie Josepha Foest , Patryk Ryczkowski, Andrew Hacket-Pain, Michał Bogdziewicz

Climate change is reducing the supply of sound seeds available for forest regeneration, creating a need to identify management strategies that can counteract these losses. Managing local tree density offers one potential approach, as neighbouring trees can enhance pollination but also increase losses to seed predators. In masting species, which produce highly variable but synchronised seed crops, the balance between these benefits and costs may depend on annual reproductive effort. Here, using seeds collected beneath 314 European beech (Fagus sylvatica) trees across three stands in Poland and the United Kingdom over three years, we examined how conspecific density within 5–50 m buffers influenced pollination efficiency, pre-dispersal seed predation, sound seed production, and seed mass. During the high-seed year, predicted sound seed production increased almost 2-fold from low to high conspecific density, coinciding with a tendency for seed predation to decline with increasing density. In contrast, during low-seed years, seed predation increased with density, while pollination efficiency increased with density in one of two years. Mean seed mass decreased by approximately 9% with density in a high-seed year. These findings suggest that dense neighbourhoods can increase the number of sound seeds available for regeneration when their predation costs are weakened by high seed production. Future studies should determine whether greater seed supply outweighs reduced seed mass in its effects on seedling establishment and survival. Maintaining higher local densities of reproductive trees may therefore help sustain sound seed supply during mast events and partly buffer the consequences of masting breakdown for European beech regeneration.