Vegetation development in a stormwater management system designed to enhance ecological qualities

Urban green areas can provide ecosystem services such as biodiversity conservation, recreational and educational services, and local climate regulation including stormwater management. Implementation of sustainable urban drainage systems (SUDS) allows for development of designs targeting desired habitats or species groups. This study investigated short-term changes in a plant community following implementation of a SUDS designed to enhance nature quality of a 4.8 ha urban grassland in Lynge, Denmark. Dry basins allowed for water detention with construction entailing terrain modifications, seeding of target species and changes to water dynamics, resulting in four treatments differing in soil conditions and water regimes. Plant species richness and composition were documented before (2012) and two years after (2015 and 2016) implementation of the SUDS. A floral resources index was composed to assess the quality of the flora as foraging resource for four groups of bees. Plant species richness, alpha- and beta-diversity as well as frequency of target plant species significantly increased after SUDS construction, as did floral resources for bees. Increased alpha diversity was primarily seen in areas around dry basins, while the increase in overall beta-diversity related to a shift in plant community composition within dry basins. The SUDS construction also changed dominance relationships among plant groups as forb cover increased at the expense of grasses, and cover of seeded and post-construction naturally colonising species increased. Two years after construction this study confirms potentials of SUDS to enhance ecological value of urban grasslands, when targets for ecological enhancement are integrated in the SUDS design.