Extensive Green Roofs (EGRs) and the Five Ws: A Quantitative Analysis on the Origin and Evolution, Aims, Approaches, and Botanical Views

Extensive Green Roofs (EGRs) are nature-based solutions that provide several environmental, health, social, and economic benefits. This review of about 1430 scientific papers, based on the five Ws, When, Where, Why, Who, and Which, aims to understand how interest in these important green infrastructures originated and developed, as well as the nature of such academic research. Special attention was paid to the way researchers approached plant selection. Furthermore, this review made a detailed quantitative evaluation of the growth in interest for such green infrastructures within the scientific literature, which began mainly in Europe around the middle of the last century before spreading to America and Asia, growing rapidly during recent decades. The main impulse behind the study of EGRs came from the fields of engineering and architecture, especially on the themes of thermal mitigation and runoff reduction. In decreasing order, we found the categories aimed at ecological and environmental issues, substrate, and pollution reduction. We also found little evidence of collaboration between different disciplines, with the result that botanical features generally receive little attention. Despite the ecological benefits of plants, not enough attention has been given to them in the literature, and their study and selection are often limited to Sedum species.