1. Urbanization and Sustainability
Exponential growth of the world population has occurred only for the last 100 years, where it more than quadrupled: 1.6 billion in 1900, 2 billion in 1930, 3 billion in 1960, 4 billion in 1975, 5 billion in 1987, 6 billion in 1999, and presently approaching 7 billion [
2]. Noteworthy is that the world urban population grew much faster. Population migration to live in cities and metropolises is a global trend. Presently about one in two people live in urban areas, which is estimated to increase to two out of three in 2050 [
3]. Some estimates point to an even faster growth, where the urban population will reach about 61% in 2030 [
2]. For example, in Europe approximately 75% of the population lives in urban areas and estimates point to approximately 80% in 2020 [
4], representing the urbanization level of most industrialized nations today [
5]. In the USA
circa 80% of the population lives in urban areas [
6]. One of the most urbanized nations in the world is Australia with more than 92% of its population concentrated in six State capital cities and other urban areas [
7].
New megacities (>10 million) are growing in the developing world. The population in India (1.2 billion) has more than doubled during the last 50 years, but the urban population has grown nearly five times. These authors estimate that by 2021 the number of mega cities in India will increase from the current three (Mumbai, Delhi and Kolkatta) to six (including Bangalore, Chennai and Hyderabad), whereby India will have the largest concentration of mega cities in the world [
8]. In China, since the “reform and openness policy” in 1978, urbanization has seen a tremendous boost, most prominent in the Pearl River Delta region during the past two decades, where urban areas have grown as much as 300% between 1988 and 1996 [
9]. Economic growth and demographic changes will accompany growth in urban populations, especially in populous China and India, producing ever-greater demands on services that nearby and distant ecosystems provide [
5]. Considering mid-sized cities (between one and five million inhabitants) urbanization rates have been steadily increasing globally, which will have profound impacts on natural and agricultural ecosystems, e.g., as reported by [
10] to occur in China. “The merits of compact development were extensively debated in the 1970s. Critics questioned the claimed environmental, transport and costs benefits, and argued that was contrary to market forces towards sprawl, the decentralization of work and residents’ desires. Debates focused largely on developed-country contexts and centrist approaches, but attention shifted to the merits of centrist versus decentrist compact development in the 1990s” [
11].
Opposed to the concentration of urban population in large monocentric, high-density, and frequently compact cities is another important form of urban development—urban sprawl or the so-called “diffused city”, which has increased during the last decades worldwide. It is broadly characterized by a dispersed spatial pattern of a mix of urban land uses, where four characteristics dominate: low-density, scattered development (
i.e. decentralized sprawl), leapfrog development, and commercial strip development, and is associated with unplanned incremental urban development [
4,
12,
13]. Typical in the USA in the early part of the 20th century, it was promoted by the utopian city vision of Frank Lloyd Wright’ Broadacre City of 1935 [
14]. Later this phenomenon proliferated to other parts of the world. In Europe, where cities were traditionally much more compact, urban sprawl is now a common phenomenon and regarded as one of Europe’s major challenges [
4]. And it is the most significant and urgent issue in American land use [
15].
An alternative, intermediate form of urban development is through a polycentric or multiple-nuclei structure, which some define as being compact [
13]. Polycentric development is a form of decentralized concentration of numerous small- and medium-size urban centers, frequently (but not restricted to being) organized around a compact city center, forming large urban agglomerations. This concept was introduced in urban geography by Harris and Ullman in 1945, representing an evolution from multi-center city to multi-center city region or polycentric city region. The process of sub-urbanization associated to a large city originated numerous settlements located in its surroundings. From this original concept a more complex urban pattern evolved, especially in Europe—polycentric urban regions, which are made up of numerous polycentric city regions [
16]. Polycentricity can emerge from two distinct set of relationships: (1) intra-urban patterns of population and economic activity clusters, e.g., Los Angeles, London or Paris; (2) interurban patterns such as the Randstad-Green Heart complex in the Netherlands, the area of Padua-Treviso-Venice in Northern Italy, the Southern California urban region, and the Kansai area in Japan [
17]. Other distinctions of polycentric forms are made according to its evolution process: some emerged as a result of households fleeing from the city center to the suburbs, followed by the relocation of firms, and services—the centrifugal mode; others via a coalescence of existent cities and towns of similar dimension into contiguous functional urban regions. Examples of the latter are the Randstad, the Rhine-Ruhr metropolitan region, and the Flemish Diamond [
18]. This urban form “seems to have become one of the defining characteristics of the urban landscape in advanced economies” [
17]. Since the last decade or so the polycentric approach has been widely implemented in the European Union as a cornerstone of its spatial development policy [
19]. There is a sufficient agreement “about the desirability of a polycentric urban structure organised on small and medium-sized, compact centres, well connected through an efficient network of public transport” [
12].
Landscapes are being subjected globally to dramatically significant changes due to the continuous urbanization process and a strong use (and misuse) of earth resources [
20]. Urbanization is the most dramatic form of irreversible land transformation, affecting both landscapes and the people who live in and around cities [
21]. Although urban population growth over the past century has occurred on a very small portion of the global terrestrial surface (<3%), the impact of cities has been global, with 78% of carbon emissions, 60% of residential water use, and 76% of wood used for industrial purposes attributed to cities, affecting energy flows, biogeochemical cycles, climatic conditions, biodiversity and ecosystem functioning and services far beyond its limits [
2,
5,
21]. As Eugene P. Odum describes it: “Great cities are planned and grow without any regard for the fact that they are parasites on the countryside which somehow supply food, water, air, and degrade huge quantities of wastes” [
22].
Novel approaches are needed to address the complex issues arising from increasing world population, depletion of resources and decreasing quality of human habitat. A more holistic way of thinking must be adopted to reduce global environmental stresses [
23]. The sustainability paradigm has emerged from these global issues. Sustainability is a powerful but hard-to-define concept that confronts many disciplines, including planning. Sustainable planning is inherently multi-dimensional, aiming to assure the viability of ecological, social and economic systems presently and into the future [
24]. Sustainability is the capacity of the earth to maintain and support life and to persist as a system [
25]. This concept adopts a systems perspective being relevant to systems ranging from the global to the local scale. It strives for natural resource management consistent with the preservation of its reproductive capacity [
22,
26]. Recently sustainability science is emerging, focusing explicitly on nature-society interaction dynamics, and promoting inter- and transdisciplinarity perspectives, where landscape ecology should and would make significant contributions [
27]. Many scientists believe that promoting sustainability is the over-arching goal of landscape (and regional) planning [
28]. Cities must play a more central role when looking at global sustainability for several reasons [
29], including the fact that they have increasingly sizeable ecological footprints [
5,
22,
30,
31], notwithstanding that “(…) cities epitomize the creativity, imagination, and mighty power of humanity. Cities are the centers of socio-cultural transformations, engines of economic growth, and cradles of innovation and knowledge production” [
31], and that they represent arguably the most important habitats for humans [
2]. “A sustainable city must achieve a balance among environmental protection, economic development, and social wellbeing. Urban sustainability requires minimizing the consumption of space and resources, optimizing urban form to facilitate urban flows, protecting both ecosystem and human health, ensuring equal access to resources and services, and maintaining cultural and social diversity and integrity” [
31]. It is not surprising that one of the key research priorities in landscape ecology is the integration of ecological research into urban policy, planning, design, and management strategies [
32].
This paper is centered on the (landscape) ecological dimension of cities’ sustainability, with a particular focu s on horizontal or chorological processes from a regional perspective [
33,
34]. The hypothesis set forth in this manuscript is that cities can improve their sustainability by adopting intermediate, network urban forms such as polycentric urban systems under a broader vision (as compared to the current paradigm), to make way to urban ecological regions. This regional vision considers three main components: a network of cities, towns, and rural villages linked by corridors—ecological, e.g., hydrological networks, cultural,
i.e. transportation and information infrastructures, and multifunctional (ecological + cultural); a multifunctional hinterland of rural and natural resources aiming at increasing regional self-reliance, structured by a network of ecological systems that provides for key-ecological services (the region´s “ecological backbone”); and the interrelationships between cities and their functional hinterland. Landscape ecology principles such as holism and systems theory, and its basic tenet—the relationships between ecological and cultural patterns, processes and change, are combined with complexity science in order to cope with uncertainty to improve regional systems’ resilience. Cooperation in its multiple forms is seen as a fundamental social, but also economic process to the urban network functioning, including its evolving capabilities for self-organization and adaptation.
4. Strategies for Self-Reliant Cities
Strategies for self-reliant cities emerging from a new thinking context include local production for local consumption [
22,
33,
29,
65,
70,
73,
77] local markets and ecological commerce [
29,
139], multifunctional, redundancy and modularization for the hinterland’s ecological infrastructure [
78,
79] and maximizing circular organization (or closed loops) of inputs and outputs [
22,
29,
41,
70,
71]. The keywords are “reduce, re-use, and recycle" (the 3Rs). The use of local materials and techniques boosts the regional economy [
138]. Local markets bring together production and consumers, and the community as a whole, e.g., as proposed for London’s 160 sq km of farmland by the Sustainable London Trust [
29]. In this context a new understanding of economy is urgently needed, as for example the so-called “ecological commerce”: “Economic development, the foundation for human settlements, seldom acknowledges ecological limits in either capitalist or socialist systems. However, the ecological footprint demonstrates the need for economic restructuring aligned with the natural world. Sustainable urban development therefore needs an ecology of commerce. Such an economic system would move beyond resource conservation to promote adaptive reuse of existing natural resource and built resources, emphasize renewable resources, and restore environmentally degraded areas such as brownfields. As an example in the USA, Chattanooga, Tennessee is committed to eco-commerce. It has created lucrative new industries such as electric vehicle production, ecotourism” among others [
139]. Gauzin-Muller provide for extensive examples in Europe, namely twenty-three on the “environmental approach” to architecture of housing, public buildings, and commercial and service buildings, and six on urbanism and sustainable development [
138]. Beatley provides also for numerous examples in Europe, from ecocycle balancing in Stockholm (Sweden), to Ecover—a sustainable factory in Oostmalle (Belgium), an ecological approach to commerce and economic development in Graz (Germany), or industrial symbiosis in the eco-industrial park (EIP) of Kalundborg (Denmark). Ecocyle balancing in Stockholm is promoted via sewage treatment plants that produce energy (biogas) and fertilizer (to be re-introduced in the farms nearby) [
29]. The municipality of Graz contracted with farmers to accept and compost (source-separated) organic and lawn wastes collected in the city farms (located within a 60-km radius of Graz) and then apply to their fields. Farmers are paid providing an additional source of farm income, as well as a way to substantially reduce the city’s composting costs. Finally, at the finer scale of houses and buildings bioclimatic design, based on site conditions and buildings shape and orientation, promote the rational use of energy [
138].
5. Case-Study—Kalundborg
Kalundborg is a city of 50,000 inhabitants located on the seashore of the island of Zealand,
circa 100 kilometers East of Copenhagen, Denmark (
Figure 1). Here we can find the first EIP formally identified as such, later followed by others, e.g., in Styria, the Austrian province where the city of Graz is located (see above), and in the Ruhr region (Germany) [
140]. Despite its small population Kalundborg is the largest industrial center on the island with an industrial turnover similar to that of a middle-sized European city, and is still growing. The area includes e.g., two of the world’s leading producers of enzyme and insulin (Novo Nordisk), the largest water treatment plant of Northern Europe and the second largest oil refinery of the Baltic Region (Statoil). On the other hand, due to the heavy-industry located here, there are, among others, pollution problems to be solved, e.g., the production of green-house gas (GHG) emissions: Kalundborg is responsible alone for
circa 9% of the total Danish CO
2 emission. However, and according to the municipality, Kalundborg is striving to become a green industrial municipality by 2020; its policy is to make compatible its continued growth with the protection of the environment [
141].
Figure 1.
Industrial symbiosis. The Eco-Industrial Park (EIP) at the coastal city of Kalendborg, Denmark. The photo shows the location of the major industries that incorporate the EIP.
Figure 1.
Industrial symbiosis. The Eco-Industrial Park (EIP) at the coastal city of Kalendborg, Denmark. The photo shows the location of the major industries that incorporate the EIP.
“An EIP is a community of firms in a region that exchange and make use of each other’s byproducts, in the process improving their environmental and economic performance. The argument is that by working together, this symbiotic community of businesses achieves a collective benefit that is greater than the sum of the individual benefits each company would realize if it optimized its individual performance only” [
140]. EIP are based on the concept of ‘‘Industrial Symbiosis’’. IS is a central concept in the industrial ecology literature, which describes geographically proximate inter-firm relationships involving the exchange of residual materials, water, and energy. Here one industry's residue is another industry's resource through a structured exchange of resources: water, energy and other industrial residues are exchanged across company boundaries [
141].
All started in 1961 when Statoil, an oil refinery newly installed in Kalendborg started to use surface water from Lake Tissѳ in order to save the existent limited supplies of underground water. Mind that water is a scarce resource in this part of Denmark. This project was developed together with the municipality. The reduction in the use of ground water has been estimated in
circa 2 M. m
3/year. Later a number of other collaborative projects were introduced and the number of partners gradually increased. By the end of the 1980s, the partners realized that they had effectively "self-organized" into what is probably the best-known example of a working industrial ecosystem, or an industrial symbiosis. Note that the IS is based upon commercial agreements between independent partners [
142].
Currently, the EIP is made up of seven key industries and Kalundborg Municipality. Hereby we describe four of them. Asnӕs electric power station, the largest in Denmark, is at the core (
Figure 2). It provides residual heat to the municipality that feeds up the district heating system, replacing highly polluting oil burning heaters in individual homes, and to another major player—Statoil, presently Denmark’s largest oil refinery. Asnae produces other valuable by-products including 170,000 tons/year of fly ash, which is used in cement manufacturing and road building, e.g., by local construction firms. Finally it supplies also a fish farm. The power plant uses salt water, from the fjord, for some of its cooling needs, helping to reduce withdrawals of fresh water from Lake Tissø. The resulting by-product is hot salt water, a small portion of which is supplied to the fish farm’s 57 ponds [
143,
144]. Gyproc, Scandinavia's largest plasterboard manufacturer, uses the power plant's fly ash to obtain gypsum, a by-product of the chemical desulphurization of flue gases. Gyproc purchases about 80,000 tons/year, meeting almost two-thirds of its requirement. By purchasing synthetic gypsum from Asnæs, Gyproc has been able to replace the natural gypsum that it used to buy from Spain. Statoil surplus gas, which used to be flared off, begun to be treated in 1993 by removing sulfur, which is sold as a raw material for the manufacture of sulfuric acid. The clean gas is supplied both to Asnӕs and Gyproc as a low-cost energy source. Gyproc switch from oil to gas recorded a 90–95% saving in oil consumption. Finally it supplies its purified wastewater as well as its used as cooling water to Asnæs, thereby allowing this water to be "used twice" and saving additionally 1 M. m
3/year of water. A large pharmaceutical company, Novo Nordisk has its largest production site in Kalundborg. The factory site is shared with Novozymes, Local farmers make use of Novo Nordisk's by-products (sludge) as fertilizers. Industrial enzymes and insulin are created through a process of fermentation, the residue from which is rich in nutrients. After lime and heat treatment, it makes an excellent fertilizer. Some 1.5 M. m
3/year are delivered to local farmers, free of charge [
144].
Figure 2.
The several components of the industrial (eco) system at Kalundborg, Denmark and its interrelationships, including the flows of energy and materials between the several players [
145].
Figure 2.
The several components of the industrial (eco) system at Kalundborg, Denmark and its interrelationships, including the flows of energy and materials between the several players [
145].
The positive environmental impact appears to be substantial: on an annual basis, CO
2 emissions are reduced by 240,000 tons, 3 M. m
3 of water is recycled,
etc. In addition numerous by-products should be added, which are sold to industries located outside the industrial cluster. In addition to these reductions, the use of the excess heat from Asnӕs for household heating has eliminated the need for about 3,500 oil-burning domestic heating systems [
141].
The original motivation behind this industrial cluster was to reduce costs by seeking income-producing applications for unwanted by-products. Gradually companies realized that they were generating environmental benefits as well [
141]. It is a win-win situation. The Kalundborg industrial ecosystem could serve as a beacon to sustainable planning aiming at increasing self-reliance of cities [
144]. Many policy analysts argue that public planners can copy and even improve on Kalundborg. However some argue that “The planning of a community of companies in a region that exchange and make use of each other’s byproducts has been advocated in many academic, business and political circles. The real world examples that justify such an approach, however, were entirely the result of market forces” [
140].
Contributing to the gradual and evolutionary process initiated in 1961 there seems to be several keys for success [
29]:
The energy crisis of the 70s and 80s prompted many of the energy efficiencies;
The economic benefits and an enhanced environmental image: “(…) environmental altruism has little to do with the symbioses that have been developed” ([
29], p. 244);
The flexible and cooperative Danish regulatory systems (see a discussion on the difficulties to develop such an approach in otherwise less flexible regulatory systems, e.g., in the USA [
140,
146]);
Physical proximity of the companies involved in the process in an area of circa 4 km2, and the fact that Kalundborg is a small town, with a strong sense of community (see below);
5. Cooperation and complementarity between the companies, the municipality, local environmental NGO’s, and others actors. The governance system led by Asnӕs—the environmental “club” started in 1989 with the abovementioned main players, that promoted discussion and brainstorming in order to expand this symbiotic system.
There are further lessons that we can learn, derived from some comments from those directly involved:
- All contracts have been negotiated on a bilateral basis;
- Each contract has resulted from the conclusion by both companies involved that the project would be economically attractive;
- Opportunities not within a company's core business, no matter how environmentally attractive, have not been acted upon;
- Each partner does its best to ensure that risks are minimized;
- Each company evaluates their own deals independently; there is no system-wide evaluation of performance, and they all seem to feel this would be difficult to achieve.
Jørgen Christensen, Vice President of Novo Nordisk at Kalundborg, identifies several conditions that are desirable for a similar web of exchanges to develop:
- Industries must be different and yet must fit each other;
- Arrangements must be commercially sound and profitable;
- Development must be voluntary, in close collaboration with regulatory agencies;
- A short physical distance between the partners is necessary for economy of transportation (with
- heat and some materials);
- At Kalundborg, the managers at different plants all know each other” [
143].
According to P. Desrochers “numerous EIPs have been planned in North and South America, Southeast Asia, Europe, and southern Africa” ([
146], p. 345). THE EIP concept is also extending to developing a food and agriculturally focused EIP (
Figure 3) [
147].
This real-world case-study illustrates the need to further incorporate in city planning, design and management much of the emergent concepts presented in earlier sections in this manuscript. Cities will not be completely self-reliant in a near future. As we could see it takes time to build such systemic relationships as those in Kalundborg EIP. Furthermore some argue that the known examples of success were not planned activities (see above); Kalundborg EIP emerged as a result of self-organizing capacities of the many players involved: industry, municipality, agro and fish-farmers, NGO’s,
etc. It is important to acknowledge that, purposefully or not, the Kalundborg industrial cluster was envisioned as a system, where components (players) are interacting through a bundle of horizontal (or chorological relationships) flows of energy and materials. Across time a circular organization with a network pattern emerged—the EIP, showing similar characteristics as those in living systems discussed earlier (
Section 2.3). Here we can recognize some of the principles of systems and complexity theories and of the science of landscape ecology (see
Section 3.3).
Figure 3.
The concept of Agro Eco-Industrial Parks [
147].
Figure 3.
The concept of Agro Eco-Industrial Parks [
147].
The metaphor of urban metabolism is also applicable to Kalundborg (see
Section 2.6). Inputs and outputs are integrated to the benefit of all, reducing some of the exports coming from outside the city, sometimes very far such as the natural gypsum coming from Spain to Gyproc. Linkages were established between the city and its hinterland, e.g., via the input of fertilizers for local farming or fly ash to local construction firms.
Notably the IEP was achieved via cooperation between institutions (governance mechanisms) and complementarity across companies and other actors (actors with different functions which input-outputs feed into each other in quasi-closed loops). These are two most important characteristics of polycentric urban systems (see
Section 2.7 and
Section 3.3)