Trends and gaps in global research of greenery systems through a bibliometric analysis

This study presents a critical review analysis of greenery systems research through a bibliometric approach. The purpose of this study is to provide a holistic overview by (i) the development of the field; (ii) the research trends and the main issues; and (iii) the main gaps still observed in the literature. Therefore, this paper provides the past, the present and the potential future of this scientific topic and serves as an orientation and guide for researchers who aim for a better understanding of the main progress and gaps. A detailed analysis of 1918 documents found in the Scopus database for the 1974–2019 period was conducted. Content analysis of titles, keywords and abstracts revealed that most of the research has focused on the study of green roofs. Previously this topic was dominated by water runoff analysis, while recent contributions acknowledge greenery as an effective microclimate mitigation strategy, especially in urban areas. The United States was the most productive country, representing almost 20 % of the total documents. Over 86 % of the relevant documents were published since 2009. Overall, research on this topic is increasing, with new methods and directions but some gaps remain particularly on the areas of environmental impact, costs, health, outdoor thermal comfort, and vertical greenery systems.