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The objective of this assessment is to explore how the aspects of scale, diversity and resilience apply to cities. In particular we explore the concepts of urban ecosystems and metabolisms, using Panarchy Theory as a framework to help explain the rise and fall of cities in light of resource exploitation and flow (im)balances. Scale, diversity and resilience are considered specifically from the perspective of enabling conditions to achieve and maintain a healthy urban system state, subsequently deducting important implications for urban planning and design.
Cities as Systems subject to Adaptive Cycles
There is truth to the city analogy of “urban jungle”. Like their natural counterparts cities can be considered as complex eco-systems, the latter which have been defined as a “set of interacting species and their local, non‐biological environment functioning together to sustain life’’ (Moll and Petit 1994).
In urban environments these eco-systems interact with social systems, with reciprocal feedback loops and varying degrees of interdependence (Folke et al. 2010). Such ecosystems provide us what we consider to be ecosystem goods and services, which are “benefits human populations derive, directly or indirectly, from ecosystem functions” (Constanza et al. 1997).
If cities are systems, they can be considered in light of adaptive cycles, as described in Panarchy Theory (Gunderson and Holling 2001). The adaptive cycle represents a system’s movement through four successive, repeating phases, while adjusting or adapting to the external environment as it changes. In here it’s assumed that at every level of time, scale and space systems are semi-autonomous, subject to random perturbations, surprises and un- or insufficiently anticipated events, some of which can push the system into a state of crisis challenging its ability to maintain essential functionality.
Figure 1 The adaptive cycle, characterised by four successive phases (Walker and Salt 2006)
The adaptive cycle is considered to come with fore and back loops. In the fore loop systems find themselves in a period of resource accumulation with focus on rapid growth and exploitation followed by a search for stability and conservation. As systems mature they become more connected, but also more rigid at the loss of resilience. In the back loop part of the cycle systems go through rapid change with dissipation of their economic, social and natural capital. As a system rapidly loses potential and becomes increasingly disorganized, destructive and creative forces allow it to transform in order to find new resilience. Eventually the system reorganises itself, with innovation and experimentation flourishing (Eason and Garmestani 2012).
How systems respond to internal and external forces depends on their inherent potential (the range of variability that can occur without transforming the system’s function and structure); internal controllability (degree of connectedness between controlling variables that lend rigidity or flexibility to the system); and its adaptive capacity or resilience. Resilience can hereby thought of as the robustness or strength of an urban system to withstand stress, and its adaptability to respond to changing conditions and objectives (Emmi 2012).
We’re not there yet though. Perhaps cities should be thought of as a dynamic nested set of adaptive cycles, characterised by large, slow moving cycles integrated and interacting with smaller, fast moving cycles. The larger cycle may respond to and nurture the creative reorganisation phase of a smaller, faster cycle to help it bring to scale, while the collapse of a smaller cycle in the destructive phase may propagate upwards if the larger mature cycle is vulnerable to disruptions.
An example would be the American city of Detroit, where its overreliance on automotive industry eventually caused it to collapse. The exodus of industry and residents has now led to the birth of a thriving urban agriculture scene on vacant plots, contributing to the revival of Detroit in unexpected ways. This suggests that specialized cities may enjoy initial success, but the lack of a diverse economic base can reduce their adaptive capacity, leading to significant destruction before a reinvention phase is eventually being entered (Glaeser and Saiz, 2003).
A key to survival in the adaptive cycle may therefore mean to dynamically foster adaptive capacity while simultaneously creating new opportunity. This according to Holsinger (2013) would enable a state of ‘dynamic stability’ whereby a system can absorb or reflect external influences without being significantly disturbed by it (resilience). Another way to consider the stability of the urban ecosystem has been proposed by MacArthur (1995) by measuring the number of alternative pathways it contains through which energy can flow. An abundance of pathways he argues tends to equilibrate fluctuations in the system (diversity). In either case one could argue what we need most: stability or transformation?; as ‘bouncing back’ to a stable state could point at a return to long-term unsustainable development patterns. This in turn ties in with the concept of scales, i.e. “the levels at which phenomena occur both in space and time”, advocating for longer-term systemic transformation of cities in order to achieve a desired, resilient state. (Chelleri 2015).
That this is an important consideration shows in the way we speak of adaptive cycles, suggesting that cities will eventually always revive and recover if faced with destructive forces and rapid loss of resilience. This may not always be the case. History has seen cities flourish and perish, which leads us to briefly consider the patterns of change within system dynamics.
Emmi (2012) notes that there are six key patterns of change (figure 2), representing the various ways in which systems evolve in relation to the resources that sustain them. Such patterns occur as part of the system’s trajectory through adaptive cycles, while the (2nd) “exponential decay” change pattern in which systems face rapid decline as a result of wasteful use of an exhaustible resource could even lead to an adaptive cycle coming to an end. This is what some believe may have led to the disappearance of several great Mayan cities in Central-America, placing resource demands upon the surrounding environment that grew beyond the capacity of the land.
Figure 2 Patterns of change in relation to the use and availability of resources sustaining a system (Emmi 2012)
Cities and their Flows
As discussed earlier ecosystems provide humans with a range of so-called ecosystem services. In urban environments these can come, according to Ervin (2012), from natural sources (e.g. rivers), intermediate sources (e.g. reservoirs) or built replacement sources (e.g. waste water treatment). Such services are strongly embedded in the wider ‘urban metabolism’ of a city, a catch-all concept representing the flows of water, energy, materials and nutrients through the urban environment. For many centuries for instance, the resilience of human settlements has been closely related to the availability of food and water within close proximity (Kampelmann 2014).
|Figure 3 Example of a visualisation of the urban metabolism –focusing on energy sources (grid electricity, wind energy, heat, geothermal, CO2)- of the Dutch city of Rotterdam (IABR 2014)|
An inventory of a contemporary city’s urban metabolism will in many cases display inefficiencies and imbalances in resource in- and outflows as a consequence of modern consumption rates, as well as the generation of waste and emissions. Not only magnitude but also quality of the flow patterns are of essence. When we look at fresh water brought into the city, the outflow may consist of contaminated waste water, leaked water from faulty pipelines, and used water being released in saline nearby coastal environments (e.g. sea) rather than being retained to replenish local groundwater tables (Kennedy 2007).
From a Circular Economy perspective a healthy urban metabolism therefore displays efficient resource use and flow patterns, with a high degree of circularity in terms of its flows (Villaroel Walker 2014), and where resources are constantly channelled towards their highest quality use (upcycling). In energetic terms this is known as ‘exergy’, the maximum useful work possible from a particular energy form. Some argue (Daly 2007) that one means to help achieve such a state would be through proper pricing or valuation of the ecosystem goods and services that are being provided.
Implications for Urban Planning and Design
In recent decades many cities have moved into or seen themselves shifting from a conservation towards a release phase (figure 1) as part of the adaptive cycle. Key reasons frequently point towards unsustainable resource use, resource-inefficient planning and design practices, insufficient diversity and resilience at one or more scales, and the socio-economic implications of such developments. This ranges from single-sector cities (low diversity) in Europe which thrived during the industrial revolution but lost out as globalisation meant that production moved elsewhere, American suburban sprawl cities which increasingly face the (financial) consequences of resource-inefficient planning characterised by low-diversity neighbourhoods not designed at human scale, to emerging and often highly diverse Asian megacities which see themselves faced with the challenges brought about by rapid population growth in combination with increases in wealth (resource demands), as well as weak governance and planning structures that can result in low resilience.
This shows that for cities to retain a healthy state it is not a matter of being either diverse, resilient, efficient or built at suitable scale; rather it’s a matter of having all of these in the right combination. In order to thrive, cities like other eco-systems will therefore have to seek balance, a state that is also known as the “window of vitality”, where a system’s key enabling conditions interact in an optimum manner.
Figure 4 The Window of Vitality (Fullerton 2015)
What lessons can we draw from this for urban planning and design? First of all, diversity is a key ingredient of resilience and enhancing the diversity of the various systems which comprise our cities may increase our ability to thrive and bounce back from human and natural induced shocks and stress, such as climate change. Diversity can also create beneficial redundancy whereby negative impacts of the failure of system components can be contained rather than affecting a major part of a city.
In this respect it pays to consider the concept of functional redundancy. Where different species play a very similar role in the ecosystem, critical functions can be performed by either. In the drive for greater efficiency, it is easy to overlook resilience benefits that redundancy in key functions can bring. Functional insurance on the other hand can buffer an ecosystem against externally imposed stress by having multiple species with similar functional effects but different functional responses (Diaz and Cabido 2001). This creates response diversity, whereby a disturbance is unlikely to present the same risk to all components at once (SRC 2014).
Contemporary cities instead frequently address urban challenges through single-purpose infrastructures and systems, managed as separate silos. Institutional structures may run along similar divisional lines, with not uncommonly poor communication between them to address cross-cutting issues. The solutions designed focus on single challenges, through use of capital-intensive fixed physical structures, rather than addressing multiple in a simultaneous matter. An example is a waste water treatment plant versus an urban wetland, providing ecosystem services comprising water treatment, recreational space, water storage and rainfall overflow (GIZ 2014).
Another aspect refers to the (local) scale of system components and how they are interconnected. A central power plant can cripple a city in case of a power-cut, whereas a diverse electricity system consisting of larger and smaller modules including so-called ‘distributed energy resources’ (DER) -which generate energy locally and can be decoupled to create ‘energy islands’- allow for lower probability of damage or failure in one part of the system to cascade (ResilientCity.org 2012).
Furthermore scale also impacts on feedback sensitivity of the system. Tight loops can lead to reduced system leakage and improved efficiencies (e.g. ‘eat local!’), enhancing the balance between network components at different (geographical) scales while supporting resilience by quickly detecting and responding to changes in the system. In cities, sufficient urban density is a key foundation for loop tightness, allowing for reduced time and costs to move information and matter through the system (ResilientCity.org 2012).
The 21st century sees many cities grappling with the challenge of how to effectively provide for its (often growing) urban population and maintain or improve service levels; meanwhile facing high/rising resource consumption levels, development patterns that may turn out costly and/or risky in the long run, as well as external threats such as climate change.
Adaptive cycles can help us frame and better understand the development and position of cities over time. This may inform strategies that contribute to balancing a city’s urban metabolism flows by actively incorporating the aspects of appropriate scale, diversity and resilience in urban decision-making. By doing so we start to acknowledge that cities truly are systems, with complex interconnected structures, the physical elements of which provide us with a broad range of (eco)system services. Appreciating how such systems work and most importantly, thrive, is essential to let cities successfully position themselves within the dynamic ‘window of vitality’.
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