Managing light and nutrients to restore plant diversity in temperate woodlands

Abstract

Restoration efforts increasingly focus on light-enhancing treatments to create open forests with high biodiversity. However, climate change and forest eutrophication, driven by atmospheric nutrient deposition and shifts towards tree species with high-quality litter, pose risks such as vegetation ruderalisation and suppression of nutrient-sensitive oligotrophic species. This study presents the first experiment combining canopy opening with litter removal, a strategy potentially reducing nutrient loads, in a species-rich oak-hornbeam forest in Central Europe (Czech Republic). We established a split-plot experiment with two partially thinned plots (30 % canopy openness), comprising 8 paired subplots: one with litter removal and the other as a control. Paired plots were also established in an adjacent closed-canopy forest. Regardless of litter removal, vascular plant richness increased significantly in open-canopy plots by the second year, with the highest richness observed in open-canopy plots with litter removal from the third year onwards. RLQ analysis combining compositional data with species traits revealed a clear effect of canopy opening, while also showing that litter removal in thinned plots favoured oligo- and mesotrophic species typical of open habitats, such as thermophilous oak woodlands and dry grasslands. In contrast, nutrient-demanding species characterized by greater plant height were favoured in thinned plots where litter was retained. Litter removal had no significant effect in the closed-canopy forest, suggesting its effectiveness depends on sufficient light availability. Our findings show that combining canopy opening with litter removal can prevent vegetation ruderalisation and support the establishment of target understorey species of open woodlands.