Thriving under multiple stressors: Performance of drought-tolerant perennials and their suitability for infiltration swales

Infiltration swales are considered an essential and multifunctional component of water-sensitive urban design. To maintain their functionality, a robust planting is required. However, species selection poses a major challenge due to the extreme site conditions. To identify stress-resistant species, container experiments with 60 perennial species native to Germany were used to investigate their performance and responses to multiple stressors typical for urban swales receiving traffic area runoff. As plant performance is more severely affected if multiple stressors occur rather than single ones, test plants were exposed to de-icing salts, cyclic flooding, and drought. Species were selected primarily for their drought tolerance, as it was assumed that their adaption to drought might also be advantageous for the other stressors. The resistance to drought was examined in a reference group and was approved for 90 % of the experimental species. With a low mortality rate of < 25 %, 72.2 % of the species confirmed as drought tolerant also proved robust to the multiple stressors of an infiltration swale and are therefore recommended for use. Considering all experimental species, significant effects of the multiple stressors compared to the reference group were only found in mortality and a visual vitality score. Data on growth height, chlorophyll fluorescence, and phenology (e.g., flowering time) did not differ significantly between the groups. However, there were large species-specific variations to be considered and investigated in further research. The study serves as a basis for a resilient greening of urban infiltration swales with native species. It is essential to their implementation, as more research is needed to date.