Urban liveability, health and wellbeing are intricately linked to large, quality, biodiverse green spaces, not densification

Résumé

Having been debated for almost three decades, the question whether cities can be both dense and green is not new (Haaland & van den Bosch 2015, Artmann et al. 2019). The framing has often been posed as a binary choice between what are generally portrayed as two mutually exclusive goals, i.e. either dense or green (McDonald et al. 2023). However, there is considerable variation around the relationship between grey infrastructure cover and population density on the one hand, and the area of green space or tree canopy cover on the other (McDonald et al. 2023), indicating that some sites have succeeded in achieving both. Indeed, examples from both Global North (e.g. Denmark (Samuelsson et al. 2021)) and Global South contexts (e.g. Curitiba, Brazil (McDonald et al. 2023)) demonstrate that dense cities can also be green. Such examples show that it is not a question of "if" they can be both, but rather (i) "what" forms it might take, (ii) "how" it can be achieved across different and complex socioeconomic and governance contexts and (iii) how to ensure it is equitable across communities and social groups at appropriate scales. Such examples also bring into question whether densification alone is the primary driver of quantitative declines in urban green space and tree cover (and associated ecosystem services), as observed in cities around the world (e.g. Wang & Yuan 2017, Nowak & Greenfield 2020, Lian et al. 2025). In raising these questions, we seek to deepen the debate by incorporating eight other dimensions of urban greening forms and processes that need to be considered if the goal is to design and develop liveable urban neighbourhoods that promote human and ecosystem health and wellbeing (Fig. 1). Each of these is briefly considered individually in the rest of the article.Much has been made of new, more compact, forms of urban greening as a means to integrate greenery into dense neighbourhoods and cities, such as vertical gardens or living walls, green roofs, green facades, balcony gardens, pocket parks, Miyawaki forests, and greening of transport or infrastructure corridors using swales or street trees (Manso et al. 2021, Dong et al. 2023). Whilst these are welcome innovations in cities and neighbourhoods dominated by grey infrastructure, most are extremely poor surrogates for connected and sufficiently large spatial areas of greenery with rich species-and structural-diversity that offer multiple provisioning, cultural and regulating services to a range of community needs aligned with their local preferences and cultures. This is based on the wellestablished ecological principle that species richness and diversity are strongly related to patch size and connectivity (Beninde et al. 2015, Ma et al. 2023), amongst other things. Thus, the small size and low biodiversity of these innovations for dense cities cannot provide the same diversity, quality and quantity of ecosystem services. For example, a child clearly cannot play in a vertical garden, and the small area of most green roofs (Appolloni et al. 2021) constrains what sort of activities can be engaged in and the quantity of ecosystem services provided. Additionally, many such compact greenspace forms cannot sustain large trees; yet large trees contribute disproportionately to the quantity and quality of regulating services (e.g., carbon sequestration, cooling capacity, biodiversity habitat) so vital to urban sustainability (Le Roux et al. 2018, Fröhlich et al. 2024)).Moreover, despite the many advocated benefits of some of these new greening approaches (e.g. rooftop gardens; Nur et al. (2022)), uptake remains exceedingly limited due to various factors such as economic constraints, initial costs of installation, a lack of government incentives, and lack of awareness (Unegbu et al., 2025). For example, in Nairobi, Kenya, green roofs represent a very small proportion of the total rooftops (about 200 buildings), and are usually in luxury apartment blocks (Njeru,2024). Similarly, in a Global North context such as Braunscheig (Germany), only 1.4 % of building roofs were deemed appropriate for rooftop gardens (Grunwald et al. 2017). Similarly, less than 0.1 % of roofs in New York City (USA) have rooftop gardens, covering only 0.15 % of the roof area in the city (Treglia et al. 2022). Additionally, they are concentrated in the more affluent areas (Treglia et al. 2022), thereby exacerbating the already inequitable distribution of public green spaces (PUGS) in the city (Niu et al. 2026).Beyond form, context is paramount in urban planning and greening. For example, consideration of the correlation between urban density and greenery, along with potential solutions to mitigate or reverse any negative relationship, has been dominated by research in the Global North, with limited contributions from Global South contexts, especially from Africa (see the reviews by Haaland &van den Bosch 2015 andMadureira &Monteiro 2021). This is problematic because the nature and rate of densification is generally very different between these two contexts, as are the uses of green space, preferences, cultural norms, and the nature of potential solutions and the capacity to implement them (Thorn et al. 2023). In the Global North, densification is typically more planned and controlled, and increasingly aligned with the planning principles of a "compact city" or "15-minute city" to promote efficiencies of scale and broad environmental sustainability (such as physical compactness, mixed land uses in close proximity, well-planned and functional public transport) (Anabtawi 2023;Bin Sulaiman 2023). In contrast, much of the densification in Global South cities is synonymous with unplanned, and often uncontrolled, urban sprawl of low-income, informal, residential areas or slums (Thorn et al. 2015, Twizerimana et al. 2025, World Bank 2026), with are comparatively rare in Global North countries (UN-Habitat n.d.). Thus, the strategies for, and forms of, urban greening are likely to be different. Additionally, promoted solutions such as vertical gardens and aquaponics have limited applicability where water, energy, and technical capacity are constrained.Greening strategies must therefore be grounded in local socio-economic and environmental realities to effectively contribute to human wellbeing, social equity and poverty alleviation.In rapidly densifying cities where land is scarce, urban green spaces must be connected and multifunctional rather than single use (Hansen et al. 2019). Multifunctional green infrastructure can deliver multiple ecosystem services simultaneously, including (but not limited to) recreational opportunities, cultural and spiritual needs, biodiversity conservation, provisioning services, urban cooling, flood regulation, and air quality improvement, all contributing to human wellbeing. For example, sustainable urban drainage systems can which delay sinks of rainwater while serving as recreational spaces. Culturally-preferred species should be planted and maintained to contribute to multifunctionality. Urban green spaces should also be connected. For example, improved connectivity of paths and wayfinding for everyday activities, or designing accessible and safe thoroughfares that promote walking and cycling (Hansen et al. 2019). Greenbelts have also been seen as an effective means to limit urban sprawl (Pourtaherian & Jaeger 2022).The design and implementation of context-specific and locally relevant PUGS must engage with the plurality of worldviews of the very conceptions of what is nature and how people relate to and use it (Shackleton & Gwedla 2021). Multiple cultures in the Global South do not see a separation between humans and nature in the way that predominates in the Global North (Cocks et al. 2016, Gauthier et al. 2025). Thus, many cultures revere nature as the home of ancestral spirits which have influence over peoples' daily lives and psychological wellbeing, requiring access to particular forms of nature for maintaining links with one's ancestors and very humanness (Cocks et al. 2016). The manicured, western-style PUGS (often dominated by non-native species (Nero 2019;Shackleton & Gwedla 2021)) established during the colonial period and still retained do not necessarily meet the diversity of needs and cultures (Shackleton & Gwedla 2021). Hence, these places do not promote a sense of "ownership and attachment to place" (Makakavhule & Landman 2020, p. 5).Some urban dwellers consequently seek informal green spaces in which to practice traditional observances and cultural rituals (Kepe et al. 2015, Adegun 2019, Manyani et al. 2021). Similarly, such informal spaces may be used as places for outdoor religious practices and worship (Ngulani & Shackleton 2019). Informal green spaces may also be used for the collection of particular plant species used in traditional cultural or spiritual rituals which contribute to cultural identity and individual wellbeing (Cocks et al. 2012, Dhyani 2024, Rahayu et al. 2025), as well as for household provisioning, such the collection and use or sale of firewood, wild foods and medicinal plants (Garekae & Shackleton 2020, Somesh et al. 2021, Rahayu et al. 2025). The grazing of formal and informal PUGS by urban livestock is also pervasive in some Global South regions, requiring different design features and plant species that tolerate herbivory (Shackleton et al. 2017, Thorn et al. 2023).The extent of greenness in relation to human, or grey infrastructure, density is an inadequate measure or goal if it is not equitably distributed and accessible so that the benefits for health and wellbeing are available to all urban dwellers. Currently this is not guaranteed, with multiple studies showing the inequitable distribution of PUGS, street trees and private gardens in both Global North and Global South contexts, with racial minorities and/or lower income groups usually having the least (Venter et al. 2020, Allegretto et al. 2022, Giombini & Thorn 2022). This is paradoxical because wealthier urban residents have greater access to private green spaces (such as domestic gardens) (Treglia et al. 2022), whilst also having the financial means to travel to access quality PUGS within or beyond the city (Thorn et al. 2023). Yet, as cities densify, the loss of private green space through infill development and vertical expansion increases reliance on PUGS. This exacerbates the already inequitable distribution of and access to PUGS in the city (Niu et al. 2026) and the associated ecosystem services derived from those spaces. For example, in Antananarivo, Madagascar, Han et al. (2025) analysed land surface temperature alongside a greenspace exposure Gini coefficient to identify spatial inequalities in access to urban cooling. Their findings revealed that approximately 25% of neighbourhoods experience significant disparities in greenspace exposure, with cooling benefits disproportionately concentrated in certain areas. Considerations of equity need to be embedded in spatial plans for new neighbourhoods as well as when older neighbourhoods are revitalized through urban greening projects. In the latter case, greening initiatives can drive urban gentrification (Reed-Thryselius 2023, Oscilowicz et al. 2025). This can be avoided with careful preparation and a genuine commitment to respectfully engage local voices and different local groups in the design, implementation and 'ownership' of the greening initiative (Rigolon et al. 2020, Oscilowicz et al. 2025, Schusler & Krings 2025).While there is already a wealth of literature on the benefits of urban greening to human health and wellbeing (see syntheses by Davand et al. 2023 and the reviews by Reyes-Riveros et al. 2021, andHan et al. 2024), small or fragmented green spaces are unlikely to provide the same measure or quality of restorative benefits as larger, more biodiverse PUGS. For example, narrow green strips along roads, pocket parks or views of vertical gardens on neighbouring buildings are unlikely to provide the same level of immersive nature experiences that support mental health compared with larger and structurally diverse PUGS (Deng et al. 2020, Rehman et al. 2023, Arifwidodo et a. 2025). While small PUGS are preferable to no green space at all, increasing urban density may mean pocket parks can become overcrowded. In some cases, this can discourage residents from using them at all (Arnberger 2012). High levels of crowding in small PUGS may therefore limit the level of mental health benefits (Cox et al. 2017, Zhan & Zheng 2026). Additionally, larger PUGS are typically more species and structurally rich (Beninde et al. 2105, Ma et al. 2023), which further contributes to mental health because the restorative and mental health benefits of access to nature are greater in spaces with higher animal and plant species richness (actual or perceived) than less biodiverse ones (Fuller et al. 2007, Dallimer et al. 2012, Methorst 2024). Moreover, it has been shown that urban residents appreciate more biodiverse green spaces than low biodiversity ones (Fischer et al. 2018), which also corresponds to a greater diversity of ecosystem services provided. Thus, we need to move beyond just a debate around density and 'greenness' and associated tree cover or green area targets, to one that includes green space quality as reflected in species-, functional-and structural-diversity.Spatial planning must be proactive and reach beyond the current city limits. Recognizing that both sprawl and densification lead to the loss of natural green spaces, we call for more pre-emptive governance and forward-looking institutions. Urban planners should identify and plan for suitable and species-rich spaces on the urban periphery to be protected so they are not transformed into grey infrastructure or informal settlements as cities expand. PUGS and green belts must be designated before formal or informal development occurs. Tools such as strategic environmental assessments are needed to identify where the green belts and PUGS of the future will be. This should also be extended to the mapping and preservation of large trees. Designation of spaces should account for diverse uses, such as traditional healers collecting plants, children playing soccer, and flood and temperature mitigation. Sufficient emphasis should be made on enforcement of boundaries to prevent encroachment by elites or informal developments, prevention of dumping, and degradation.Across the Global South, informal and formal green spaces contribute to household income and wellbeing, especially of the poor and more vulnerable (Shackleton 2021). This is through provision of household consumptive needs such as firewood, wild foods and medicines, through to small-scale income opportunities, such as roadside nurseries (Molla et al. 2020), urban agriculture (e.g. Lizarralde et al. 2025) and the selling of consumer goods (cool drinks, food, cellphone and shoe repairs) and services (e.g. wedding photography, guided tours) in and around parks and tree-lined pedestrian walkways (Thorn et al. 2025). There is a thus a need to generate synergies of interrelated development goals (Pasquini & Enqvist 2019), alongside investments in grassroots capacity building, and vocational training (Thorn et al. 2021), to effectively contribute to poverty alleviation. PUGS design and planning can also be more proactive in designing more pro-poor green spaces through various means (Shackleton et al. 2024).In considering the question posed by this special collection, we conclude that it should be reversed. It is not a question if, or can, dense urban settings also be green, but rather, can we afford for any urban setting, dense or otherwise, not to be sufficiently green and biodiverse? The evidence of the positive relationship between urban greenery and urban species richness on the one hand, and human health and wellbeing on the other, is irrefutable (although mediated by local context).Therefore, if we wish cities to be healthy and liveable places, the provision of sufficient, accessible, species-rich, quality and well-maintained PUGS, greenbelts and corridors should not be a question to be debated, but a human right to be demanded and respected. As stated by McDonald et al. (2023) "there can be no excuse for designing neighbourhoods that lack abundant nature: the tools are out there to create dense and green spaces to live in". Thus, we need to move from debating whether it is possible, to ensuring it is done through necessary context-sensitive policies and regulations, accelerated actions, zoning, appropriate city and local governance, participatory design and implementation with local communities and the sharing of best-case examples and strategies (as well as challenges and failures). We have suggested eight considerations that we feel urban planners, decision-makers and parks departments should engage with when planning, building and maintaining new towns and neighbourhoods, or seeking to make older, established areas more attractive and healthier (for the environment and for the residents). The first two require a mind-shift to accept that the local context on the one hand, and the complexity of designing for multiple ecosystem services, multiple outcomes and multiple preferences and needs, on the other, are crucial in developing and implementing context-relevant and workable designs and plans. These two foundational precepts dictate that there will not be any "one-size fits all" blueprint, set of targets or approaches. But taken together with the other six considerations will result in greener, more biodiverse, healthier and more equitable cities for all urban citizens and the biodiversity and the environment which are necessary for this to occur.

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