Again and again I come across the comparison of man and nature . And usually the story is that we as mankind approach things to simplistic or to reductionist, , we break down things in little pieces which we optimize, while nature organizes in great complexity and integral.
Especially in Sustainable city planning or Urban environmental management approaches this discussion pops up: To regard cities as ecosystems, and treat them like that In other words : we have to treat them like that and use a complex integral approach .
But is that so? Is nature as complex as we think? How does a ecosystem work in fact, is that a complex interaction between species, creating a high resilience , with species dependent of each others in and outputs? Yes and no. Yes, in the sense that ultimately, when a snapshot is taken, all is complex and interconnected . But has it been planned interconnected and complex? The answer is no. Wat nature does is filling niches: There is some space, some light , some spare nutrients, and this space is not reserved for a specific species with the right in and outputs. The space remains empty until a species passes that eco-space, hangs around and after a while is able to maintain itself . Accidentally. The species can come from anywhere. And while this species grows and survives, others will adapt, profiting or diminishing. In fact its quit simple and random, and certainly not complex. “ the Darwinian mechanism includes no concept of general progress or for optimization.” As the evolutionary biologist Stephen Jay Gold summarizes. 
Of course, when millions of years go by, at first sight a complex organization exists, after all kinds of adaptations, with disasters inbetween. But nothing has been planned , or was subject of controlled organization.
Fred Pearce recently wrote a whole book on this subject: The New Wild. About the difference in approach of the climax ecosystems supporters and the nature is individualistic adepts. The dispute has long ago been settled in favor of the individualistic adepts. And he concludes: “there is no optimal or superior system, since disruption is essential for evolution”. 
Now what about the city? In the basis it works the same. People come and go, find their place, and there is nothing complex about that: A project developer goes around in town, trying to develop any spot he comes across, until he scores and can proceed developing. Shops find their own niche in town. The problem is that people, city planners, politicians want to order things and make it complex.
It might seem more effective to plan some infrastructure, instead of let it develop randomly. And to agree on driving right ( except for some niche island species…) , and to give fines when people don’t adapt, in stead of letting traffic finds its own way. In nature these routes and structures are not planned, and develop random.
In a city these two movements come together: ‘Cityspecies’ ( shops, hotels, parkings, etc) that find their own place and optimal spot, and the ‘cityorganizers’, that want to maximize their planning and steering influence. Thats what makes it complex. Of course, In mega cities the complexity has grown beyond control , and random development wont work anymore.
However, some of these random developments can still be seen: Shopping boulevards that grow outside the cities, are not fully planned, its a species that finds their own spot,and profits from existing available structures in in and outputs, like roads with passing pollinators. Its was not planned like that, and therefor “cityorganizers” have now started in the Netherlands to “solve this problem” since its not the architectural view they like: these ‘mega boxes’ in the flat dutch landscape. It gets complicated again, by humans, not by nature.
Interesting by the way is a project in some municipalities under the Shared Spaces program by the EU. One of these is the town of Drachten in The Netherlands, where all traffic signs and lights where removed. The traffic has to find its own way again. And what was the result? The amount of accidents decreased spectacular. 
But climate change and resource scarcity, will demand that we develop sustainable cities? And so we have to tackle these ‘complex’ problems? Some years ago I made a first attempt to analyse this, and I called the city a Orbanism, A Urban organism, and stated that the wasteful system (for resources and energy use) should learn to behave more efficiently, right, like a real species . 
The idea has been developed somewhat later in the Urban Harvest approach, and applied in the analyses of a urban district. How can we redevelop the area in a self supporting area, everything is grown or produced within its borders: a zero impact built environment. The approach was reductionist: Everything broken down in parts, and by technology, or better by conversion method  . A masterplan for energy was made ( broken down in production and consumption, and per function) and a similar one for materials, water and food. Optimized partial plans: Put on top of each other to merge in a total plan. Which shows conflicts: the energy plan wants to insulate all houses, the materials plan has no room for materials production. So it gets complex? No, not really: the more effective solution from materials and energy together was to not insulate the houses, and just produce more heat. In this reductionist way all issues where tackled. Which also led to the proposal for Laundry shops, that have much less impact compared to everyone its own laundry machine: a straight forward way of deduction. But there is more,: this simple approach turned out also to provide solutions for problems, that are thought to be more complex, as a “bycatch”: Laundryshops will create local employment (while laundry machines are produced abroad) , and increases social contacts,, the much desired involvement of people in their neighborhood increases.
Another solution was to re-introduce bathhouses , the more favored solution regarding water, material and energy , which also increases social contacts … But this did not make in the ultimate plan, that was a too simple approach for people with their complexes…
The currently popular smart city approach completely neglects this simplicity, and thrives by complexity : but then solves the wrong questions, it tries to steer complexity. This is improving bad solutions , and increasing once grown complexity , while real solutions might be somewhere else: think of digital apps to operate laundrymachines (which are not the solution) , or making them more energy efficient: extrapolating on existing structures, in stead of unraveling the grown situation into basic but different solutions.
This is not meant to be a in-depth study of the issue, just a straight forward exploration. And that leads to the conclusion that nature is not complex, but people make it complex. We should not try to manage constructed complexity, but go back to the origins, to reductionist and pragmatic solutions.
1 Stephen Jay Gould: http://arnoldia.arboretum.harvard.edu/pdf/articles/483.pdf
2 Fred Pearce: The New Wild, see also: http://thebreakthrough.org/index.php/programs/conservation-and-development/deliberate-nature
3 Shared Space:
4 Post Carbon – or Post crash – managing the Orbanism ,Ronald Rovers , World Transport Policy & Practice Volume 14. Number 4. April 2009 : http://www.eco-logica.co.uk/pdf/wtpp14.4.pdf
5 Urban Harvest: case Kerkrade West: link: http://www.maxergy.org/urban-scale/