Commentary: Eco-sustainable cities - a realistic concept?

Preface

There is a global awareness of the necessity of attaining sustainability. Creating sustainable cities is thus also high on the agenda of planning professions. Cities are currently not sustainable, and with deteriorating global conditions and urban decay, the elaborate design of manicured parks and formal open spaces will need to be reassessed.

Traditional urban open-space designs that focused on scenic beautification, exotic plazas, fountains, sculptures, monuments, and amenities such as sophisticated recreational facilities will likely prove to have been inappropriate in the light of an eco-sustainable vision.

These open spaces do not contribute to eco-sustainability, and the cost of implementation and upkeep will render them irrational and nonviable. Our hope for sustainable urban living lies in critically assessing standard models of open space planning and pragmatically implementing nature’s model of ecosystem design.

Problem Statement

Extensive research across various environmental indicators suggests that humanity is on a trajectory toward ecological disaster (Sakariyahu, 2024; Berwyn, 2025). The United Nations Secretary-General has consequently issued a stark warning of an approaching "ecological abyss," underscoring the severity and urgency of the situation (Guterres, 2021). A fundamental transformation toward sustainability is imperative, particularly in urban land use—where approximately 90% of the global population inhabits just 10% of the Earth’s surface. With urban populations projected to increase by nearly 2.5 billion people by 2050, the scale of the challenge is unprecedented. Paradoxically, while modern cities are often celebrated as symbols of human advancement, they are frequently characterized by high stress levels, poor health outcomes, and extreme population density. Moreover, they are responsible for approximately 70% of global greenhouse gas emissions. Rather than embodying "landscapes of hope," many urban areas are increasingly characterized by environmental degradation, air pollution, homelessness, and social unrest. Considering these challenges, the futuristic concept of “smart cities” raises a critical question: could technological innovation and data-driven urban planning offer a sustainable path forward.

The UN Sustainable Development Goals (SDGs)1 envision cities and human settlements that are “safe, resilient, and sustainable” by 2030; only five years from now. However, living conditions continue to deteriorate. Addressing issues such as environmental degradation requires, amongst other, the creation of environmentally friendly open spaces, integrated into circular economies. If we ae to work towards a positive hopeful future, we will have to seriously question the current emphasis on so-called “well-designed” urban open space where the emphasis is often still on aesthetics and amenities.

Urban open space

Open space categories

Formal hard surface open space areas such as paved squares, boardwalks, pedestrian roads, rooftops and monuments serve specific utilitarian functions, primarily catering to social and experiential needs. In contrast, green open spaces offer scenic, recreational, and ecological benefits.

Table 1 summarizes the value categories of open spaces. Category A encompasses areas where design and construction take precedence, primarily facilitating gatherings, social interactions, and efficient pedestrian movement. Category B includes spaces where nature is present but requires artificial maintenance, such as lawn mowing and irrigation. Category C consists of areas with indigenous vegetation, which offer vital recreational opportunities and serve as retreats from urban congestion. The highest ecological value is found in Category D, where green spaces are effectively interconnected to form ecosystems that enhance ecological sustainability. Metropolitan Urban Open Space Systems (MOSS) (McHarg, 1971) plays a crucial role in keeping biodiversity and supporting environmental resilience. Seen from the perspective of ecological sustainability, such nature orientated open space is to be seen as integrated biodiversity corridor systems. For urban open space to provide in the specific need of humanity, its value is to be assessed.

Value of urban open space

From a socio-psychological level, urban environments are recognized as depriving individuals of nature's many benefits. The weekend exodus of city dwellers to rural areas highlights their deep-seated need to reconnect with nature. To compensate, urban residents cultivate home gardens, keep pets, install bird feeders, and nurture potted plants. According to the TGM Global Pet Care Survey 20242, approximately 59% of South African households have pets.

The Kampala Capital City Authority (KCCA)³ actively promotes urban greening through initiatives like the "Kampala Goes Green" tree-planting campaign.

The city of Lagos manages multiple nurseries, open spaces, and beautification projects aimed at enhancing green coverage and public access to nature.4  From a real estate perspective, buyers are willing to pay 7% more for homes with exceptional landscaping and 58% more for properties with water views (Gullone, E., 2000). The Urban Natural Assets for Africa (UNA) programme, led by ICLEI Africa, has developed a series of handbooks to guide cities in integrating natural assets into urban planning^.5

The concept of biophilic design (Beatley, 2011) highlights humanity’s innate need to connect with nature for both survival and personal fulfilment. Cities should go beyond simply incorporating parks—they should be designed to fully immerse people in natural environments. Consider the practice of forest bathing, where individuals take therapeutic, stress-relieving walks—often barefoot—through forests, engaging their senses by touching, rubbing, and smelling leaves. Research supports the benefits of such connections with nature. Fitzgerald(2024:114) found that city dwellers are 20% more likely to experience anxiety than those in rural areas. Similarly, urban residents living near large greenspaces are significantly less likely to suffer from poor mental health (Myers,2019).

Green cities

Consequently, most cities feature parks, and there is a demand for a variety of types. Central Park in New York is arguably the most famous example of a large green space located within a city. Its significance is evident in the fact that no one would propose selling this land to real estate developers. However, the key question remains: do existing parks truly provide an experience of authentic nature? Do they meet the psychological need for green spaces among residents of densely populated cities?

Most vegetation in parks consists of exotic species that create what can be described as “visually pleasing yet ecologically barren” landscapes. These need intensive maintenance, including added irrigation, trimming, manicuring, costly fertilization, and herbicide applications.

However, despite the widely acknowledged value of ecosystem services, ecological factors are rarely prioritised when developing open spaces (Semeraro et al., 2021; Steyn, 1992; Spellerberg, 1994). Instead, the allocation of natural open spaces is often treated as a purely numerical exercise—meeting a minimum percentage of land that must be "sacrificed" instead of using it for real estate development.

Ecoservices

It is well-known how nature functions as an integrated, dynamically organised system in which each element and every organism has its specific place and function (Odum, 1975). Everything is connected organically and dynamically to an integrated system. Bringing nature into cities, (or conservation of natural habitats in cities) implies the management of ecosystems, inclusive of all natural elements - vegetation, micro- and meso-animals, integrated with the water, air, rock, soil and climate of the city – with humans as (top) omnivore.

The urban areas have the same natural elements as nature, but their roles differ. Like in nature, the driving force in cities is also energy.

Cities need enormous amounts of energy. For a city to be an ecologically independent self-sustainable unit, energy should be coming not from the sun alone but from internally available renewable sources: solar, wind, geothermal, biomass, hydrogen, etc. But cities are excessive and inefficient users of energy. The main reason for the unsustainability in terms of energy use is the conversion (manufacturing) of raw materials into luxury consumer items such as television sets, fast foods, and amenity gardens. The 2nd Law of Thermodynamics shows that energy cannot be reused, emphasising the fact that we have limited energy resources, also in the city. Ecological laws also teach that 90% of energy is lost between subsequent trophic levels. The shorter the food chain, the more productive the system is (Hugo & Hugo, 2025). Expressed in urban terms: the longer the production line, the more energy is lost; or rather, the more non-essential articles produced, the more waste is generated, and the more energy is wasted. Instead of energy flowing mainly to the 1st production level (processing food and basic requirements), much energy is wastefully ploughed into subsequent levels. This has the effect that all cities rely heavily on imported fossil fuels, with their ecologically detrimental and unsustainable effects. An example of unsustainable practices where energy is wasted and ecoservices ignored is where fallen leaves in parks, which is nature’s system of fertilizing, are collected and transported in already congested (polluted) traffic lanes, to overloaded dumping sites. Then artificial fertilisers, manufactured at great environmental cost, are transported back and applied in parks. Planting exotics instead of endemic vegetation, which needs additional energy or their upkeep, is another obvious example.

In cities, as in nature, matter is transformed into resources by energy. Manufacturing is dependent on the availability of matter. The 1st Thermodynamic Law teaches that new matter cannot be created. The fact that materials (minerals, timber, etc.) for manufacturing must come mainly from sources outside of the city makes cities unsustainable. If existing urban areas can introduce perfect recycling, it can go a long way towards sustainability.

Food also cannot be adequately produced within the city, but the import of produce can be reduced by urban farming in green belts, horticulture, and permaculture as well as improving the recirculating processes. In Manchester, as in  many similar situations, residents transformed schools and neglected alleyways into vibrant community gardens with planting of fruit trees and vegetables instead of flowers and lawns (Al-Othman, 2024).  

Like the use of matter, the water cycle in cities is unsustainable. Water needs to be transported from distant reservoirs to meet demand, including the irrigation of “thirsty” non-endemic plants in gardens and parks. The role of rivers and marshes as “kidneys,” and that of vegetation acting as the "lungs" of the city environment, plays a vital part in enhancing the sustainability of cities. Apart from the educational and ecological value of zoos and domesticated pets, animals such as e.g. the role of bees, birds, and soil organisms,) play a vital role in the ecology of cities. Biodiversity is, however limited in the urban environment.

Thus, these ecoservices are freely available yet not incorporated optimally in cities. All elements of matter (resources) are connected and driven by energy in an interconnected system. This should be the model to follow if sustainable cities are to be attained.

Urban systems

For a city to be ecologically sustainable, it should thus fit harmoniously into the surrounding natural system as a sub-system. The Earth is a “closed” system since no matter is added to the system from outer space (Figure 6). According to the 1st Thermodynamic Law, matter cannot be demolished, nor can more be added. Notwithstanding the constant use of matter through all trophic levels, it thus stays stable within the Earth system. It is a sustainable system with perfect recycling of matter. Individual ecosystems on Earth, however, can be “open” systems where energy flows through and matter is exchanged with their environment, creating a dynamically balanced situation, provided the inflow and outflow of matter are equal.

A city is a human construct and does not function perfectly according to environmental laws like an ecosystem. In an ecosystem, all available matter circulates perfectly, resulting in no residual matter that accumulates as pollution. The only driving force in nature is the energy from the sun. The urban system, however, requires added external energy inflow (electricity) and resources (matter). Some circulation occurs within the system, but it produces an enormous mass of wasteful outflow of pollutants in the air, water, and discarded products on the surrounding land and sea. As illustrated by Figure 8, the used matter (water, materials, produce, etc.) is continuously being replaced artificially from outside. It is an unsustainable system that is kept in dynamic balance by way of human management. The system will stop functioning when human input is no longer available.

In Figure 9 as a schematic illustration, is given to show the comparable typical size of input and output of resources and pollution in a city. Input of water and output of sewage being the main components influencing lack of sustainability. Ironically, these are the easiest sectors where sustainable balance can be created bycatching rainwater and recirculating household and sewage output. 

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No city can thus do without external input of matter. Resources include water and energy (electricity) but also a lot of raw materials such as building materials (e.g., cement), minerals (e.g., iron ore), wood, fibre materials (e.g., wool), food and much more. If the fabrication of goods from these resources could be produced internally and recycled, it might eventually be possible to reduce the import of matter into the city and thus approach a situation of near-sustainability. The system is currently unsustainable; however, the level of sustainability can be raised. It depends on how much matter (resources) can be 1) kept inside (circulated), and 2) generated within, in the system, i.e., striving towards a closed system. Figure 10 shows a diagram illustrating how the inflow of matter is imported, effectively circulated, and the amount of (proportionally smaller) residuals exported as waste.

For true environmental sustainability, cities should thus run as closed ecosystems, as illustrated in Figure 6, with all trophic levels ingrained into a negative circular feedback system; effectively using all ecoservices without externally added resources, and perfect circulation of existing matter.

Ecological viable cities

The traditional premise is that a city is an inorganic (ecological sterile) intrusion into the natural (living) environment. It is regarded as the antithesis of nature. The greening of cities is seen as a struggle between the two opposites: nature vs cities.

Urbanization is sometimes equated with cancer growing into “uncontaminated nature”. But more sensible reasoning shows that cities are rather healthy living organisms; a tree spreading its roots harmoniously into the environment. If, in nature, beavers use wood to build dams, is it unnatural to use sand and cement to build our dams, or use clay bricks for houses?

Green open space should be treated not as an afterthought (bringing back that which has been lost due to urban expansion) but as the guiding force in city planning. Should we strive to bring (elements of) nature into cities, or do we need to build cities harmoniously into nature? Building a city into nature implies that urban design needs to analyse the topography, hydrology, soil, climate, etc. and then place urban structures to match the directives of nature. Following Ian McHarg’s philosophy: “Design with nature” (McHarg, 1971). Ridges and waterways should guide the urban plan.

Forman & Godron (1986) compare a city with a biological cell with specialised structures and transmissible memory written in its nucleus. But the city is more like a multi-cell heterotrophic organism that gets its energy not (only) from the sun but from the surrounding environment.

Similarly, the renowned environmentalist Eugene Marais (2006) in his studies showed that an anthill.

The only difference from (other) animals is that it does not have the faculty of movement. The city is analogous to a biological creature. Like arteries in an organism, cities have networks of streets, pipelines, transmission lines that transport resources (food; fuel; water), services (electricity; telephones; health), etc. to “cells” i.e., houses and service centres such as factories. Interrupting any one of these (e.g. electricity supply or removal of waste) will lead to the breakdown of the system. Cities are governed by ecological laws just like humans and all forms of land use should adapt to nature’s directives to survive sustainably (Hugo & Hugo, 2024(2)).

One can thus compare a city and its parts and functions, with that of a living organism. But whether a city can function sustainably, is questionable. Figures 11 and 12 are simplistic portrayals of the elements of a food chain in a city comparable to that of nature.

The provision of raw materials to the city from the countryside (such as raw materials, water, chemicals, food products) is comparable to the soil and soil organisms, water, and nutrients that we find in a natural ecosystem. The role of the production of products from these resources in a city (e.g. factories) can be equated with Trophic level one (T1 - primary production) in a natural ecosystem’s food chain. Factories and production of commercial products are thus the equivalent of the photosynthesis process, i.e. the production of basic produce. Wholesalers can be equated with primary consumers at T2 – (i.e. herbivores in nature) who use the primary products. Retailers (T3) are using products from wholesalers (T2) and send them to consumers (T4) higher up in the system. Humans, as top consumers, fulfil the role of omnivores in nature as well as in the city.

Any system can only be sustainable if all the trophic levels are in dynamic harmony. (See Figure 12). In a city the same principle of adaptation to change at any one trophic level, applies. Trophic levels in the city are in constant dynamic balance. If consumers (influx of population numbers at T4) exceed the available supply provided from the lower levels, the city will not be sustainable. Equally so, if T1 production is seriously curtailed (e.g. serious power failure), it will necessitate a reduction of produce for the upper trophic levels. Fewer wholesalers will cause a reduction in produce for retailers, i.e. a shortage of food and other goods. In nature, a shortage of water (drought) will have the effect that T2 and subsequent trophic levels will be reduced. In a city, such a situation of shortage will be overcome by human ingenuity, and artificial provision of water from outside the city will be implemented, rather than a reduction of products and users (people).

In this system the production of enough primary resources will thus be fundamental in deciding if a city can function sustainably. Basic resources such as water, food and minerals, etc. are not available in sufficient quantity. At Level T1 plants are mostly exotic and non-productive. At T2 herbivore (animals) are limited. At T4 carnivores are missing and meat must be imported into the city.

From the perspective of the inorganic elements of ecosystems, soil, water and atmosphere also do not function in sustainable fashion in a city. The air from industrial processes and exhaust gases from vehicles is not effectively cleaned by vegetation. It is thus polluted and has a detrimental impact on urban living conditions. Excessive sewage and industrial outflow also pose a challenge.

The soil is covered by hard surfaces and does not function as a basic ingredient for food production, and the water cycle is disrupted. Rainwater is removed from the city by stormwater canals, with the loss of natural river valleys with their riparian vegetation and habitats for animals, and water is imported again (using electricity) from distant reservoirs by way of pipelines. The natural eco-benefit of valleys in retaining flooding and enhancing groundwater supplies, as well as carbon sequestration and enhancing biodiversity, is lost.

Smart cities

In addressing the issues outlined in the problem statement, including stressful, unhealthy, and overcrowded conditions, it is important to recognise that, while the United Nations Sustainable Development Goals (SDGs) envision cities that are “safe, resilient, and sustainable” as well as “open spaces, integrated into circular economies” by 2030, this vision remains an ambitious and arguably unattainable objective under current trajectories.

Moreover, sustainable cities encompass far more than ecological considerations alone. They require an integrated approach that includes multiple functions such as transportation systems, commercial and industrial activities, and socio-economic, political, and cultural dimensions. Nonetheless, embedding ecological principles into the design and management of urban open spaces may serve as a catalyst for initiating the broader transformation towards genuine urban sustainability.

While futuristic "smart cities" such as The Line are often hailed for their reliance on renewable energy, they still fall short on achieving genuine ecological balance. All resources (water, food) are imported from outside, and waste generated is not effectively circulated. Without significant changes in our consumer-driven approach to resource consumption (especially in urban life) and a shift toward simpler lifestyles and our preference for aesthetics above productivity, cities will continue to exhaust their resource supplies at an unsustainable rate. Striving for ecological sustainability is essential—not only to preserve the environment’s vital eco-services but also to ensure economic stability and human well-being. “Our planet has supported life for billions of years, but …. we are testing its resilience. The alarming reality is that global warming is accelerating faster than scientists had initially predicted, and its effects, such as soaring temperatures and the rapid melting of polar ice, are more tangible every day. Human activities have accelerated environmental changes in a way that may create irreversible consequences for the planet …” (Sanz, 2025:1).

 Conclusion and Guidelines

The debate aims to explore the potential for cities to achieve elusive ecological sustainability. Comprehensive research is required to assess each city's ability to establish it.

Some general guidelines might include: Creating MOSS’s for cleaning air and water; Improving ground water and integration of all open spaces - even if some properties will have to be expropriated to enhance biodiversity by forming links for animal life to migrate in times of stress (fire, drought); and providing nature-based recreation (for socio-psychological reasons). No person should be more than 10 minutes walking from a green belt, as well as commuting and access to schools (cycle, walking lanes).

Other measures to consider are e.g. the mandatory catchment of rainwater from rooftops⁶, and energy by way of solar power, providing a mechanism of urban community gardening for residents (also using power line servitudes, road, and rail verges).

To reach urban sustainability, it is urgent to develop local small-scale regenerative agriculture within the greenbelt and associated urban fringes (Hugo & Hugo, 2024(1)).

Intensive farming practices such as vertical farming, factory farming, plant-based meat production and permaculture (Mollison, 1978) also come into play. Replacing exotic vegetation in parks with endemic species, assess pragmatic designing of open space according to ecological guidelines; revisiting the process of managing floodwater (flood retention dams and marshes instead of – or in association with - cement canals); controlled use of insecticides and herbicides in gardens and other green areas⁷; using grey water where irrigation is needed; buildings must adhere to at least 50 year building flood line, keeping in mind that this line shifts higher as hard surfaces (roads, roofs) increase; and many more.

If the water cycle and renewable energy are managed to reach its full natural potential, and maximum use is made of recycling, it could assist much in the drive towards ecological sustainability as it will save much in terms of what must be imported from outside, as shown in the model in Figure 13.  

Such ecofriendly planning and design also make sound fiscal sense. A quantitative analysis of the ecological value of urban space in the Chinese city of Liuzhou estimated that green spaces provided ecosystem services valued at U$ 7 billion that otherwise would have had to come from the taxpayers’ pockets (Li, et al, 2024).  It is therefore possible to create a hopeful future for cities through ecologically intelligent planning and management.

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