Shaping urban environments through human selection for plant traits

Abstract: Cities, as home to the majority of the world’s people, are significant sites for addressing challenges of achieving sustainability and securing human wellbeing. Urban environments are complex social-ecological systems, and meeting these challenges requires better understandings of the interactions of social and ecological elements. While there are many possible lenses through which to study social-ecological systems, this thesis examines the potential of a traits approach as one way to link ecological elements to social values. In ecology, functional traits have been defined as the characteristics of organisms that determine how organisms respond to the environment, and how they affect ecosystem processes, functions, and services. While functional traits have an established history of being linked to ecosystem processes and functions, they have only recently been extended to social aspects through the operationalization of the ecosystem services concept. As such, there is a distinct gap in identifying traits that are relevant and important to people. This interdisciplinary thesis attempts to bridge some of this lacuna, through empirical studies conducted in two cities: Cape Town, South Africa, and Stockholm, Sweden. Paper 1 addresses connections between traits and social values generally across cities through a literature review that examines connections between traits and cultural ecosystem services. Paper 2 explores preferences for traits and reasons for plant selection in the context of Cape Town. Paper 3 examines vegetation patterns and the expression of socially-valued traits across different land cover and land use classes in Stockholm. Paper 4 serves as a synthesis and comparison piece between Cape Town and Stockholm, and brings together social data on plant preferences and ecological data on plant patterns gathered in both locations under two different projects. Overall, responses from social surveys of preferences suggest that people actively select for a variety of different plant traits in the urban environment, and have a multitude of reasons for selecting the plants that they do, related both to qualities of the plants themselves, as well as broader external factors at multiple scales. Vegetation surveys of plant patterns suggest that trait preferences may be inscribed by people in the landscape, though to differing degrees. Using traits as an approach to link ecological elements to social values exhibits advantages in that traits are a spatial unit that is easily understood by citizens and environmental managers. However, it presents limitations in terms of scale, as traits are most useful in connecting to pin-point characteristics in the landscape, and social values associated with broader scales may be overlooked. Collectively, however, the papers in this thesis suggest that traits may serve as one useful approach for discerning human values in the urban landscape, and can be used as indicators of social function. In management applications, particular traits can be incorporated into landscaping interventions to provide for urban areas of greater social meaning. In this way, traits may serve as one tool within the evolving toolbox of social-ecological system study, and thus can contribute to future urban landscapes that exhibit robust social and ecological function.