Title: The Current State of Resilience Research in Urban Forestry: A Qualitative Literature Review
Abstract: In the times of enlarging cities and more people living in cities, it is essential to maintain the quality of life for everyone. Urban forests make a significant contribution to this. In urban areas, productive ecosystems are essential to maintain human health and well-being. However, problems like increasing urbanization, changing climate, and pollution in the air, water, and soil can endanger urban ecosystems like urban forests. Having or building resilient urban forests is seen as a possibility to maintain ecosystem services provided by urban forests. Under future conditions, they may become essential for human life in urban areas as some are critical for human health. This study is a literature review of past research dealing with resilience in urban forests. Forty-one articles published in the years 2006 to 2019 that complied with the search criteria were reviewed. Results show that only three articles used a definition of the resilience of urban trees after disturbance based on a formula; two articles used a definition of resilience based on natural ecosystems. The remaining articles did not define resilience while using the term in the articles. Out of the reviewed articles, four major themes were identified: urban forest management, urban biodiversity, urban soil, and socio-economic conditions. Nine articles included content about urban soils, 19 articles about urban forest management, 30 articles about urban biodiversity, and 11 articles about socio-economic conditions. As (built) urban forests in cities differ considerably from natural ecosystems, some authors rated monitoring and management actions as necessary, mainly for new establishments and the integration of new species. Authors expressed contradicting opinions on species richness. While some articles suggested focusing on native or endemic species, others proposed to increase species diversity to enhance urban forest resilience. Tolerances and resistances of tree species are essential for urban areas and may gain importance in the future, increasing extreme weather events leading to more frequent pest and disease outbreaks. Results indicated a focus on urban soil quality as a basis for plant growth, and tree health is an essential factor in urban forestry. Municipal authorities need to adapt management actions to create and maintain an urban forest to the benefits they intend to achieve for the city considering local conditions like climate, species pool, and specific resistances. At the end of the review, a framework recommends actions for a structured collaboration of municipal authorities, researchers, and citizens to achieve resilient urban forests.