Designed plant communities for nature-based solutions : an investigation of urban rain gardens

Healthy and diverse vegetation is the prerequisite for “nature-based solutions” (NbS), which is a concept that describes the intentional use of designed or managed vegetation to answer to societal challenges by providing multiple ecosystem services simultaneously and efficiently. Urban rain gardens (URG) are an example of a nature-based solution where vegetation is used to improve technical function, provide amenity values, and wildlife habitat. This thesis investigates the relevance of “designed plant communities” (DPC) as a framework for designing and managing URG vegetation. The investigation consists of 1) a narrative literature review on the history, core ideas and design tools of DPC, 2) a scoping review on DPC research and its contributions to NbS criteria fulfillment, 3) semi-structured interviews on the strategic management or URG:s in Sweden and Finland, 4) designed case studies comparing four different plant selection strategies, including DPC, with regards to their short-term establishment and development, and 5) a data collection on vegetation development in URG:s in Sweden and Finland. The narrative review highlights knowledge gaps that hinder the DPC framework’s planting design tools from reliably aiding in fulfilling DPC objectives and goals. The scoping review shows that while research on DPC provides insight into urban vegetation establishment and its short-term development, it is rarely anchored in the societal challenges that NbS seek to address, and provides little evidence on how DPC provide regulating or provisioning ecosystem services. The interview results show the unpredictability of URG vegetation development, despite the innovation and effort often put into creating URG:s. The results of the case studies also indicate that while DPC-plantings can establish and perform as well as other planting design strategies in the short term, it is not an inherently successful planting design strategy. As realized performance is more important for NbS than adherence to specific design methods, developing the DPC-framework into an evidence-based planting design practice might improve design outcomes and the framework’s relevance for NbS.