Do Cities Grow Like Ecosystems?
Until millennia, city building was an organic, bottom-up, incremental process beginning with a handful of people looking for opportunities at the confluence of waterways, trade roots, and resources. Speculating newcomers establish temporary structures, replaced over time with permanent buildings. Enterprising citizens set up shops to supply growing demands, and streets and utilities are made to service the community. The succession of cities is a reinforcing pattern; the more people and resources a city has, the more opportunities it creates and the more attractive it looks to opportunity seekers.
This growth pattern parallels processes found in nature, namely, ecological succession. Ecosystems, like cities, are opportunity engines. Beginning with bare earth, an ecosystem will incrementally add complexity in the form of diversity, biomass, and ecological connections. With enough time, even a parking lot can become a forest.
Cities, like ecosystems, are complex adaptive systems that learn and change through growth. Both systems start off with relatively few resources and connections but move toward complexity as they attract (create the conditions for) opportunity. If cities grow like ecosystems, how might ecological succession inform urban growth?
The Succession of Cities and Eight Ecological Lessons
If cities want to move through succession, we need to let them. Drawing lessons from ecology, here are eight ecological patterns that we should apply to the development of cities.
1. Grow Incrementally
Ecosystems don’t dramatically jump from earlier to later stages of succession. Growth (defined by increasing complexity) is an incremental process of many small changes and interactions. Growth without the connections to support it isn’t likely to succeed. Encourage growth by creating the conditions for connections.
City Building Implication: Growth is an organic, piecemeal, bottom-up process. Encourage growth but never allow it to leapfrog over interim development stages. Small changes learn. Big changes break.
2. Small Disturbances As Opportunities
While growth is slow and incremental, decay can rapidly move a system from later to earlier stages of succession. In ecology, disturbances such as grazing, fire, and floods reset parts of the system to earlier ecological stages. When experienced in moderation, disturbances reestablish small patches of land for early succession species. Some species have co-evolved with disturbance patterns to take advantage of and only thrive on disturbed sites.
City Building Implications: In the long run, small failures and setbacks contribute to the overall diversity and complexity of the city by creating niche opportunities. Pockets of redevelopment (regrowth) are opportunities to bring new connections to a community as long as they build upon and are nurtured by the nearby connections they inherit.
3. Tap Into Existing Connections
Seedlings sprout in the nutrient-rich soils left behind after a fire. When ecology regrows on previously occupied land, it benefits from the nutrients left behind by previous inhabitants and is supported by the later stages of succession surrounding it.
City Building Implications: Redevelopment is more likely to be successful if it can tap into the pre-existing connections of the site. In this way, the success of a development is supported by the existing system – but the relationship is mutual. The redevelopment itself is an opportunity to encourage incremental growth (an increase in complexity) of the system it occupies.
Avoid large-scale disturbances. Large-scale disturbances and development wipe an area clean of existing connections and are ecologically analogous to starting on bare rock. When starting from scratch, remember that growth is incremental (lesson 1).
“What do our communities need, and what can we do to create the conditions necessary to make that happen?”The Succession of Cities
4. Develop A Patchwork & Avoid Plantations
Ecosystems start simple and succeed into complexity. Planting a climax forest is difficult, and the result is often similar to a plantation. Plantations superficially look like forests but lack the diversity and connections of complex adaptive systems. Containing a small number of species of the same age, plantations are expensive to maintain and are prone to significant disturbances such as pests, disease, and weather/climate events.
Healthy systems are a patchwork of successional stages. While later stages of succession are more complex and diverse, a system containing many stages is more complex and diverse than a system containing only one.
City Building Implications: Monolithic, monocultural developments (large tracts of the same development type and age) are expensive to service and susceptible to system shock (changes in the market, utility costs, social cohesion, etc.). Developments of the same type and age lack the conditions to build connections. To restore plantations, reestablish a patchwork by encouraging incremental growth and small disturbances.
5. Avoid Succession Locking
Traditional conservation attempts to hold (or return) ecology to a specific moment – but that’s not how ecology works. Complex adaptive systems are, by definition, constantly adapting. When we prevent complex systems from changing, their complexity stagnates and degrades; they become maladapted, lose diversity, and become brittle.
City Building Implications: No community is complete. Cities are never finished. Preventing change is the same as encouraging decay. All communities should be encouraged to develop incrementally, and no community should be prevented from doing so.
Preventing change is the same as encouraging decayThe Succession of Cities
6. Create, Accumulate, and Cycle Nutrients
The process of succession is largely the process of nutrient accumulation and cycling. As ecosystems grow, they gradually increase their ability to accumulate and retain carbon, nutrients, and water. Along with the accumulation of resources, the number of connections increases in complex systems, which encourages the cycling of these nutrients. The capacity for resource sharing increases sublinearly with size, so larger, more established ecosystems need fewer resources (per area) to sustain themselves. If every drop of water gets used twice, the system needs half as much water. I discussed the scaling of cities in a previous article. The metabolic rate (energy and recourses needs per unit area) decreases as a complex adaptive system matures.
City Building Implications: Productive communities are able to accumulate the nutrients (businesses, infrastructure, social connection, and tax revenue) they need to fuel the next stage in their development. As they move to later stages, they require fewer recourses per unit area, providing a surplus that can fuel adjacent growth.
Don’t rob productive communities of the necessary resources to maintain and grow. Reinvest resources into productive communities until they consistently provide surplus resources above and beyond their metabolic needs.
Subsidizing succession-locked communities is a losing game as they’re unlikely to reach a stage where they can accumulate enough resources to fuel their succession. Succession-locked communities depend on perpetual subsidies. Never undermine a productive community by robbing it to subsidize a succession-locked community.
7. Respect The Margins (And the Marginalized)
As ecosystems increase in complexity, earlier stages of success continuously expand outwards at the edges. The effect is that the oldest, most mature stages of succession are often found near its core. Communities at the edge of a healthy system have immediate access to nearby connections while containing many niching opportunities. This is analogous to a mature tree providing shade and nutrients to nearby younger trees. Too far and disconnected from the forest, however, young trees can’t benefit from the connections and resources of the more established forest.
City Building Implications: Complex communities expand and support earlier stages of success at their edges. If cities have old growth, it’s found at their centre. Far-removed development can’t easily benefit from the dense connections of the old growth core. Likewise, young communities often have many unoccupied niches, which creates new opportunities. The core is simultaneously robbed without the opportunities supplied by nearby growth.
Innovation often comes from the margins (and marginalized), provided that they can access and influence the larger system. Removing access or raising the bar out of reach is a recipe for suppressing opportunities, stifling growth, and perpetuating poverty.
Small changes learn. Big changes break.The Succession of Cities
8. (Re)define Success(ion)
At each stage of ecological succession, plants and animals modify their environment in ways that create opportunities for complexity and resiliency. This strongly suggests that ecologically, “success” is the creation of opportunity.
Cities aren’t just places to live, they’re opportunity engines – that’s why we’re attracted to them. So, when it comes to the succession of cities, a good question to ask is, “What do our communities need, and what can we do to create the conditions necessary to make that happen?”