How green does a dense city need to be? Functional urban biodiversity for dense cities

Melissa Vogt^*

• Independent researcher, Sydney, Australia

Discussions about urban greenery have gone from ecological framings to cases of environmental justice and equitable access (Farkas et al. 2023). Losses due to limited preserving for densely populated urban areas is an urgent case for urban green spaces (UGS) (Vogt, 2025a), with proven implication for the natural-environment and human health. In 2015, Haaland & van der Bosch found that provisioning and preventing biodiversity loss is two of more than seven challenges identified for dense cities. Improving measures of losses, reserving, and improving the quality, as aesthetic, visibility, and functional biodiversity, of existing urban greenery, and greening in difficult sites such as narrow streets are recommended to address rapid loss and fragmentation. Green in dense cities is needed but requires localised diversity in spatial layout and design to ensure positive interactions with different Urban Open Spaces (UOS), including grey (formal and informal paved or built urban landscapes) and transparent space (air and aquatic) (Vogt, 2025b). For dense cities, small UGS of diverse sizes and shapes, corridors, vertical walls, rooftops, other elevated spaces, and pocket parks prove to provision benefits needed, and in some cases provision therapeutic effects (Vogt, 2025a). While efficiencies of cooling effect vary, with plant density and spatial distributions, parks, green roofs, and street trees can lower air and surface temperatures by up to 5*C (Lind and Li, 2025). This opinion article explains how (i) Dense cities can be green, using functionally connective small, elevated, vertical and corridor green spaces, and measuring larger sized UGS; (ii) Two categories of benefits from access to urban greenery can guide understanding of a need for urban greenery. It goes on to answer, how green? The conceptual guidance and measures of need for benefits leads to an optimised quality of life from urban biodiversity as an effective green dense city. Planning, implementation, monitoring and identifying UGS locations is responsive to local landscape measures and guided by refined wilding for dense cities. Urban planning and how it is informed and implemented is significantly determinant to answering if a dense city can be green. Space allocation, availability and strategic locations, elevated, vertical and small spaces provide better opportunities for green in dense cities.Aesthetic preferences influenced by urban cultural norms in cityscape design can be a limitation or motivator for whether a city is dense and green. This limitation could be for lack of vision, clarity, or example of how dense cities can be green. Resources required, or an understanding of resources needed could as well. Perspective changes and design options for cityscapes, buildings, UOS and surroundings including hidden green spaces might address the limitation and encourage urban green integration. Compact cities require localisation and acceptance of diversity in urban plans (Bonafantini et al. 2025). While often referred to as lower emitters with density-emissions relationship (Castelli-Quintana et al. 2021) determined by size and structure of urban areas, air pollution and other effects often experienced in urban landscapes variably require mitigation. As UGS can provide multiple functions, the following question is how green and how functionally or effectively green? Buildings and greenery are more often integrated in dense cities (Song et al. 2025) not just adjoined or separate. For a dense city to be green, design and planning that integrates built urban landscapes, grey spaces with green spaces is required, alongside defining green for dense cities, as surrounding greenery measured for benefit from access. Localised measures can lead to need for, alongside a a question of can. For dense cities, local studies of need for specific mitigative effect and or therapeutic benefits, and the feasibility of provisioning access can determine how green.I suggest conceptual guidance for imagining how green a dense city can be, and how effectively green as a significant for urban planning and design. Guidance from concepts and principles can be significant for urban form, spatial planning and configuration and vision for an urban landscape. A concept can provide a vision or imagining for how green, or even an optimised green, instead of whether it can be green, with conceptual bounds for indicators of benefit for an urban landscape. It can also generate enthusiasm for what the concept aims for, with an ability to see how an urban landscape can be green. A concept might inspire design and planning at a landscape level, with elaboration on how green is defined and conceptualised. A good concept can sufficiently elaborate for imagining and can improve the effectiveness of how green. I suggest refined wilding and functional urban biodiversity as a concept and theory (Vogt, 2025a-c), that can guide and optimise urban planning to effectively integrate, preserve and increase greenery even in dense cities. It works toward a functional connectivity across UGS types, and across three UOS, green, transparent (air and aquatic), and grey spaces (informal and formal paved and built urban landscapes). And an advanced function of UGS of different types, and function across UGS of any urban landscape. See figure 1.As a conceptual frame it can determine need for benefits and optimises effectiveness when guiding and responsive to local landscape measure planning, design, implementation and monitoring. It can also guide measures past the categories of benefit of access for optimised outcomes. It is a concept and theory applicable to any UGS type, including spontaneous and informal or abandoned UGS, with various definitions of informal compared to formal UGS to consider. The resulting UGS are semi-natural green systems, with little human hand, or human interaction or modification required. This limited need for maintaining through strategic planning, design and PTSG selections is significant for long term outcomes. The varying densities and spatial distributions and emphasis on advanced function through design and planning address effective greening for mitigation for different stressors and therapeutic benefits. It also addresses coordinated integration with infrastructure and buildings, and anthropogenic factors like use of different urban areas (Syeda et al. 2025), and aesthetic preferences for UGS, cityscapes and facades (Vogt, 2025c). Supporting concepts encourage a prioritising of nature in cities. They variably integrate adjoined built urban landscapes to the design of urban nature (Beatley, 2011) and variably define and encourage an optimised quality and configuration across an urban landscape.The quality of UGS can address ecological functions, health, and benefits of equitable access (Kabisch et al. 2017), as a mitigative and therapeutic benefit and of across UOS functions as an optimised outcome. Conceptual clarifications for renaturing, novel urban ecosystems (Vogt, 2025d, table 1;Vogt, 2025b, table 5), wildlife friendly, and biophillic design are in Vogt, 2025a-d). Two additional concepts that refined wilding complements and adds specificity to are biophillic cities and urban rewilding. Biophillic cities (Beatley, 2011) is a UGS adjoined to built urban landscape design concept. Refined wilding recognises across UOS connectivity, and aesthetic preferences as a limitation, and specifies parameters for adjoined greenery, taking biophillic cities further for the natural-environment. Urban rewilding works from rewilding originally a concept for apex predator wilding, with PTSGs being reestablished as habitat (Vogt, 2021). It is a distinct concept in terms of landscape type, and taxa focus before PTSG as habitat, as distinct from wilding for agricultural landscapes (Vogt, 2021). Urban rewilding implies a landscape consideration but is focused on returning an urban landscape to a wild landscape through rewilded urban spaces (Jin et al. 2024).Refined wilding is complementary by landscape level considerations and functional connectivity across UOS but specifies wild native and non-native non allergenic PTSG selections, and functional assemblages for various UGS types with spatial configuration and design specifically and conceptually guided by functional urban biodiversity. Effective greening for dense cities optimises configurations, functional connectivity across a landscape, with positive influential flows and integration between UOS, and different UGS types. It is mitigative, therapeutically beneficial, and protective of ESHR. How synergistic mitigation and therapeutic benefits are provisioned.I suggest mitigative effects and therapeutic benefits (Vogt, 2025b, table 2) as two categories of benefits from access to UGS. Parameters for measure reach distant, peri-urban, and across and integrated to paved cityscape UGS, and UOS, block, city, outer city and across urban landscape levels. Indirectly they are measures of quality of life and can result in lowered costs by health and even urban landscape damage and repair (Fu et al. 2025). Therapeutic benefits are summarised in sensescape, and other access categories.(ii) How functional urban biodiversity in a dense city is optimised.(Iii) How local measures of need compare to already provisioned to determine how effectively green a dense city is or could be informed by functional urban biodiversity and refined wilding principles.Optimised decision making for design, spatial planning, and equitable access to urban greenery.Equitable access to functional urban biodiversity, recognises a need for ecological knowledge (Xu et al. 2025), alongside addressing the urban landscape barriers and motivations for urban greenery, framed by human realities. Interdisciplinary and advanced knowledge coordinated by refined wilding can guide and optimise decision making (Feng et al. 2024) for spatial planning and design options for urban green in dense cities, balancing need with feasibility. The concept and this article respond to localised measures of provisioned and needed, and distanced sources of effects, and provisions. Identifying the location of allergenic PTSGs that pose significant risk of exposure The conceptual guidance encourages an understanding of source of exposure, which can be peri-urban or inner urban.Inventories such as S-API, and allergenic and non-allergenic tree species identification and assessments (Vogt, 2025b) can inform identification, and guide planning.Once located, strategies for spatial planning and functional wild PTSG selections and assemblages; replacing allergenic PTSGs and adapting behaviour around pollen season can lead to a mitigation. Refined wilding and functional urban biodiversity for new or redesigned urban greenery:non-allergenic wild PTSG selections.Replacing allergenic PTSGs with non-allergenic. Optimising spatial configurations, PTSG selections and assemblages, to reduce pollen emissions aligned with refined wilding and functional urban biodiversity.Reducing wind pollination with biotic pollination, using functional wild PTSG selections and companion planting near allergenic PTSGs, decreasing pollen emissions (Nguyen et al. 2023). Urban environment stressors can decrease pollinator activity and must be factored in, as stressors can negatively affect different UOS.Refined wilding encourages functional non-allergenic selections of wild PTSGs; and functional assemblages that mitigate against either synergistic effects, or against allergenic pollen content in the air. In advanced function, it can be responsive to pollen exposures through wild refined design at an urban landscape level and optimised spatial configuration. It therefore ensures a positive influence between UGS and transparent spaces with human realities considerations and outcomes. How green dense cities can be is answered with optimised urban planning responsive to localised measures of need guided by refined wilding to ensure functionally biodiverse dense cities that functionally influence other green spaces, and transparent and grey spaces across an urban landscape. Design, planning and strategies that reach advanced functional urban biodiversity, synergistic mitigation, and therapeutic benefits.Functional urban biodiversity introduces a designed refined wild which could be as aesthetically acceptable as traditional designs while provisioning multiple functions. It is a concept for imagining a green dense city and provides parameters for determining how functionally biodiverse it can be. A capability to design, maintain, plan, and implement, identifying appropriate UGS type selection, size, shape, and connectivity with the urban form can reach realistic answers and long-term outcomes for green dense cities, and can reach aesthetic norms and preferences for a cityscape. Hidden inclusion, street, elevated and vertical, and small space strategies, and UOS functional connectivity can realistically green a dense city.