Digging diversity: Constructed dune lakes support high plant richness but differ compositionally from natural systems

Abstract

Constructed dune lakes and slacks are increasingly used to restore wetland biodiversity in stabilized European dune landscapes, yet their ecological equivalence to natural systems remains unclear. We surveyed vascular plant communities and water chemistry in 78 dune wetlands in western Jutland, Denmark (39 constructed, 39 natural). Species frequency data were Hellinger-transformed and analyzed with redundancy analysis (RDA), variance partitioning, and mixed models to identify environmental and contextual drivers of community assembly, richness and diversity. Communities in constructed and natural lakes differed significantly (overall RDA: p = 0.001, R²adj = 0.288). pH, total nitrogen (TN), and fine benthic organic matter (FBOM), together with lake origin and area, were the strongest predictors of species composition. Variance partitioning showed a dominant site effect (pure site fraction ≈ 15% of total variance), with smaller but significant pure fractions for environment (∼6%) and lake origin (∼3%), and substantial shared fractions among these components. Generalized linear mixed models indicated that constructed lakes supported higher plant richness and Shannon diversity than natural lakes (richness IRR ≈ 2.5; both p < 0.001). Additionally, diversity increased with lake area and pH and decreased with nitrate; grazing had only marginal effects, likely reflecting low replication. Overall, constructed dune wetlands support diverse but compositionally distinct, early-successional plant species assemblages. Rather than replacing natural systems, they complement them at the landscape scale. Effective restoration should couple water-quality management (especially nitrogen control and pH buffering) with landscape-level planning to address strong site effects and dispersal limitations.