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Population ageing and shrinking are demographic phenomena with far-reaching implications for sustainability in the current context of extensive and rapid urbanization. This Perspective rationalizes their interface by (a) identifying the challenges and opportunities that ageing and shrinking urban populations will have for implementing the sustainable development goals (SDGs), and (b) discussing some emerging interventions to capitalise on the opportunities and reduce the challenges to achieving sustainability. We argue that a diverse set of context-specific technological, socioeconomic, institutional and governance interventions would be needed to leverage effectively the opportunities and minimize the risks posed by ageing and shrinking urban populations for long-term sustainability.

To ensure that cities and urban ecosystems support human wellbeing and overall quality of life we need conceptual frameworks that can connect different scientific disciplines as well as research and practice. In this perspective, we explore the potential of a traits framework for understanding social-ecological patterns, dynamics, interactions, and tipping points in complex urban systems. To do so, we discuss what kind of framing, and what research, that would allow traits to (1) link the sensitivity of a given environmental entity to different globally relevant pressures, such as land conversion or climate change to its social-ecological consequences; (2) connect to human appraisal and diverse bio-cultural sense-making through the different cues and characteristics people use to detect change or articulate value narratives, and (3) examine how and under what conditions this new approach may trigger, inform, and support decision making in land/resources management at different scales.

To capture the many complexities, we adopt a broad approach to urban governance, encompassing the diverse combinations of formal, informal and/or customary/traditional institutions and practices in urban areas of the Global South. The broad arguments are illustrated with appropriate examples and boxed case studies to illustrate important dimensions of diversity but also the scope for generalisation. In many contexts, inclusion of urban ecology, biodiversity, and green–blue infrastructure within urban governance is quite novel, thus presenting challenges to often rigid and outdated systems in times of unprecedented change. Hence, the chapter addresses key aspects needing change, including guidelines and examples of how this has been and can be achieved. A comprehensive and holistic approach is vital to provide a logical context for prioritisation and integration. This will facilitate joined-up action to achieve multiple co-benefits through targeted interventions rather than a scatter gun approach. Novel approaches that prioritise transdisciplinary co-design or co-production over conventional adversarial and top-down expert-led mechanisms have considerable potential in this regard. These are examined across relevant spatial scales, from key global agreements and conventions, to national initiatives, local authorities and the potential of transnational municipal networks.

Cities are currently experiencing serious, multifaceted impacts from global environmental change, especially climate change, and the degree to which they will need to cope with and adapt to such challenges will continue to increase. A complex systems approach inspired by evolutionary theory can inform strategies for policies and interventions to deal with growing urban vulnerabilities. Such an approach would guide the design of new (and redesign of existing) urban structures, while promoting innovative integration of grey, green and blue infrastructure in service of environmental and health objectives. Moreover, it would contribute to more flexible, effective policies for urban management and the use of urban space. Four decades ago, in a seminal paper in Science, the French evolutionary biologist and philosopher Francois Jacob noted that evolution differs significantly in its characteristic modes of action from processes that are designed and engineered de novo (Jacob in Science 196(4295):1161–1166, 1977). He labeled the evolutionary process “tinkering”, recognizing its foundation in the modification and molding of existing traits and forms, with occasional dramatic shifts in function in the context of changing conditions. This contrasts greatly with conventional engineering and design approaches that apply tailor-made materials and tools to achieve well-defined functions that are specified a priori. We here propose that urban tinkering is the application of evolutionary thinking to urban design, engineering, ecological restoration, management and governance. We define urban tinkering as: A mode of operation, encompassing policy, planning and management processes, that seeks to transform the use of existing and design of new urban systems in ways that diversify their functions, anticipate new uses and enhance adaptability, to better meet the social, economic and ecological needs of cities under conditions of deep uncertainty about the future. This approach has the potential to substantially complement and augment conventional urban development, replacing predictability, linearity and monofunctional design with anticipation of uncertainty and non-linearity and design for multiple, potentially shifting functions. Urban tinkering can function by promoting a diversity of small-scale urban experiments that, in aggregate, lead to large-scale often playful innovative solutions to the problems of sustainable development. Moreover, the tinkering approach is naturally suited to exploring multi-functional uses and approaches (e.g., bricolage) for new and existing urban structures and policies through collaborative engagement and analysis. It is thus well worth exploring as a means of delivering co-benefits for environment and human health and wellbeing. Indeed, urban tinkering has close ties to systems approaches, which often are recognized as critical to sustainable development. We believe this concept can help forge much-closer, much-needed ties among engineers, architects, evolutionary ecologists, health specialists, and numerous other urban stakeholders in developing innovative, widely beneficial solutions for society and contribute to successful implementation of SDG11 and the New Urban Agenda. QC 20200916

As cities increasingly become the dominant settlement form across the world, it is critical to gain a deeper insight into their dynamics, in order to better direct environmental management towards enhancing urban sustainability and environmental quality. People are a key driver shaping the ecological makeup of cities, not least through landscaping actions and choices. In this study, we explore social factors shaping plant selection in Cape Town, South Africa through interviews with stakeholders responsible for managing and landscaping across three land use types: private residential gardens, public parks and open space, and conservation areas. We combine an interdisciplinary, multi-scalar framework on residential landscape dynamics and a plant traits lens to structure our approach to examining the influence of social factors on plant selection across spatial and institutional scales in the city, from a bottom-up perspective. Residents name a variety of reasons for plant selection at the household scale related to plant traits, including aesthetics, utility (e.g., food provision), environmental suitability, and personal symbolic meanings. Parks managers select for ecological suitability as well as aesthetic concerns, and conservation managers select chiefly for ecological integrity. All stakeholders describe factors at other scales (e.g., property structure, government policies) that influence their plant selection. We indicate that a complementary patchwork of private gardens and public open spaces could serve as a source of trait diversity and provide a variety of ecosystem functions and services in the urban landscape, and suggest that management and policy efforts can focus on leveraging synergies towards this end. This study contributes to a greater understanding of the social-ecological dynamics in a global south city and biodiversity hotspot.

In this study we explore species richness and traits across two urban gradients in the City of Cape Town. The first is the natural-urban boundary and the second is a socio-economic gradient informed by historical race-based apartheid planning. Plant species and cover were recorded in 156 plots sampled from conservation areas, private gardens, and public open green space. The socio-economic gradient transitioned from wealthier, predominantly white neighbourhoods to poorer, predominantly black neighbourhoods. The socio-economic gradient was selected to fall within one original vegetation type to ensure a consistent biophysical template. There is a marked shift between the natural and urban plant communities in the City of Cape Town, with little structural affinity. Urban landscapes are dominated by grass, with low diversity compared to natural counterparts. A significant ecological gradient of reduced biodiversity, traits, and in turn functionality, was found across the socio-economic gradient. Wealthier communities benefit from more private green space, more public green space, and a greater plant diversity. Poorer communities have limited green space on all fronts, and lower plant and trait diversity. Plant communities with limited diversity are less resilient and if exposed to environmental perturbation would lose species, and associated ecosystem services faster than a species rich community. These species-poor plant communities mirror historical apartheid planning that is resistant to change. Based on how biodiversity, functionality, and associated ecosystem services and ecosystem stability are linked, the results of this study suggests how significant environmental injustice persists in the City of Cape Town.

The establishment of interdisciplinary Master’s and PhD programs in sustainability science is opening up an exciting arena filled with opportunities for early-career scholars to address pressing sustainability challenges. However, embarking upon an interdisciplinary endeavor as an early-career scholar poses a unique set of challenges: to develop an individual scientific identity and a strong and specific methodological skill-set, while at the same time gaining the ability to understand and communicate between different epistemologies. Here, we explore the challenges and opportunities that emerge from a new kind of interdisciplinary journey, which we describe as ‘undisciplinary.’ Undisciplinary describes (1) the space or condition of early-career researchers with early interdisciplinary backgrounds, (2) the process of the journey, and (3) the orientation which aids scholars to address the complex nature of today’s sustainability challenges. The undisciplinary journey is an iterative and reflexive process of balancing methodological groundedness and epistemological agility to engage in rigorous sustainability science. The paper draws upon insights from a collective journey of broad discussion, reflection, and learning, including a survey on educational backgrounds of different generations of sustainability scholars, participatory forum theater, and a panel discussion at the Resilience 2014 conference (Montpellier, France). Based on the results from this diversity of methods, we suggest that there is now a new and distinct generation of sustainability scholars that start their careers with interdisciplinary training, as opposed to only engaging in interdisciplinary research once strong disciplinary foundations have been built. We further identify methodological groundedness and epistemological agility as guiding competencies to become capable sustainability scientists and discuss the implications of an undisciplinary journey in the current institutional context of universities and research centers. In this paper, we propose a simple framework to help early-career sustainability scholars and well-established scientists successfully navigate what can sometimes be an uncomfortable space in education and research, with the ultimate aim of producing and engaging in rigorous and impactful sustainability science. Electronic supplementary material The online version of this article (doi:10.1007/s11625-017-0445-1) contains supplementary material, which is available to authorized users.

The city of Cape Town, South Africa’s most southwestern city, sits on a peninsula in the heart of the geographically restricted Cape Floristic Region, which is home to exceptional biodiversity. Within the city boundary are some 3,350 plant species, 190 of which are endemic to the city itself. Like all South African cities, Cape Town continues to grapple with development discrepancies that persist from unjust apartheid governance in the past and present-day challenges of urban sprawl. The population of the city is 3.7 million. Extreme poverty, with nearly 17 % unemployment, and extensive informal settlements characterize much of the City and stand in stark contrast to wealthy suburbs with freestanding homes. For the populace of Cape Town, the natural environment presents both considerable ecosystem service advantage with, for example, a flourishing tourism industry and provisioning opportunities for the urban poor, but also a significant hazard with, for example, exposure to flooding in winter from a high water table. The value of ecosystem services is an emerging concept in the environmental management arena, and environmental and conservation issues are still seen as separate to other areas of city development, and tend to receive a lower prioritization. South Africa has good environmental legislation, but this is sometimes weakly enforced due to conflicting demands, fiscal constraints, and/or lack of implementation mechanisms. Climate change predictions for the region suggest likely biodiversity impacts, but how these will play out remain unknown. An emerging interest in the role of ecosystem services in broader City management and novel conservation approaches involving civic interests all show considerable promise for the conservation of urban biodiversity in the city of Cape Town.

Several studies in recent years have forecasted global urban expansion and examined its potential impacts on biodiversity and ecosystem services. The amount of urban land near protected areas (PAs) is expected to increase, on average, by more than three times between 2000 and 2030 (from 450,000 km2 circa 2000) around the world. During the same time period, the urban land in biodiversity hotspots, areas with high concentrations of endemic species, will increase by about four times on average. China will likely become the nation with the most urban land within 50 km of its PAs by 2030. The largest proportional change, however, will likely be in Mid-Latitudinal Africa; its urban land near PAs will increase 20 ± 5 times by 2030. The largest urban expansion in biodiversity hotspots, an increase of over 100,000 km2, is forecasted to occur in South America. The forecasts of the amount and location of urban land expansion are subject to many uncertainties in their underlying drivers including urban population and economic growth. Nevertheless, the direct impacts of urban expansion on biodiversity and ecosystem services will likely be significant. The forecasts point to the need to reconcile urban development and biodiversity conservation strategies. Urbanization will also have impacts on food and food security. While the direct loss of cropland to urban expansion is of concern to the extent that high-yielding croplands are lost, the indirect impacts of urbanization due to dietary changes to more meat-based food products can also be substantial. Presently, regional and global studies that forecast impacts of future urban expansion on biodiversity and ecosystem services are in their infancy and more analyses are needed especially focusing on interactive effects of factors that drive urbanization. We conclude by highlighting the knowledge gaps on implications of future urbanization and suggest research directions that would help fill these gaps.

This chapter reviews recent literature on global projections of future urbanization, covering the population, economic and physical extent perspectives. We report on several recent findings based on studies and reports on global patterns of urbanization. Specifically, we review new literature that makes projections about the spatial pattern, rate, and magnitude of urbanization change in the next 30–50 years. While projections should be viewed and utilized with caution, the chapter synthesis reports on several major findings that will have significant socioeconomic and environmental impacts including the following: By 2030, world urban population is expected to increase from the current 3.4 billion to almost 5 billion; Urban areas dominate the global economy – urban economies currently generate more than 90 % of global Gross Value Added; From 2000 to 2030, the percent increase in global urban land cover will be over 200 % whereas the global urban population will only grow by a little over 70 %. Our synthesis of recent projections suggest that between 50%–60% of the total urban land in existence in 2030 will be built in the first three decades of the 21st century.

We are entering a new urban era in which the ecology of the planet as a whole is increasingly influenced by human activities (Ellis 2011; Steffen et al. 2011a, b; Folke et al. 2011). Cities have become a central nexus of the relationship between people and nature, both as crucial centres of demand of ecosystem services, and as sources of environmental impacts. Approximately 60 % of the urban land present in 2030 is forecast to be built in the period 2000–2030 (Chap. 21). Urbanization therefore presents challenges but also opportunities. In the next two to three decades, we have unprecedented chances to vastly improve global sustainability through designing systems for increased resource efficiency, as well as through exploring how cities can be responsible stewards of biodiversity and ecosystem services, both within and beyond city boundaries.

To understand how the world's ecosystems are changing we need to understand cities, and to create better cities we need to understand the ecosystems they depend on. The failure of most markets, government policies and even urban studies to take these relations into account has put cities, and increasingly the whole world, in a difficult position. Studies like Urbanization, Biodiversity and Ecosystem Services can help us to extricate ourselves, provided we act on the knowledge they provide (Gordon McGranahan, International Institute for Environment and Development). The challenges of urbanization are profound, but so too are the opportunities. Cities can reconcile human society and biodiversity by creating environments that are ecologically sustainable, economically productive, socially just, politically participatory and culturally vibrant. I commend this study to all who have a stake in creating ecologically sustainable urbanization for the benefit of humanity and the planet (Ban Ki-moon Secretary-General, United Nations).