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De stadsrand: Contrast of overgangszone

Article by Timon Verstoep

Have you ever wondered why designers, planners, researchers and policymakers are so interested in urban peripheries? A lot has been written about these transitions/edges between 'city' and 'country'. Every once in a while, this topic flares up again. In the last few years, the outskirts of the city have also been in the spotlight again. We read it in the news: 'cities that threaten to grow against each other' or 'every village has a new street'. I was curious whether the outskirts of the city are worth all that attention, so I started a little research and wrote my thesis about it: Ecotone urbanism. 

The housing shortage has been a topical theme for years. In addition, in the Netherlands, but also worldwide, we see that there are more and more alarming noises about biodiversity loss. I saw an opportunity in combining these two challenges. On the one hand, housing in the form of expansion, and on the other hand, the strengthening of biodiversity. And where do these two challenges meet, yes in the outskirts of the city? That's how I became one of the many who also wrote something about city outskirts.

Figure 1: A number of headlines from the Dutch newspapers that address the urgency of the two challenges, housing construction and biodiversity loss.  

A battle for the outskirts of the city, that's what we could almost call it. Because that is one of the main reasons why designers, planners, researchers and policymakers have been so concerned about urban peripheries throughout history. The classic 'battle' between the city and the 'country'. 'Red' against 'green'. But in our time, there are many more challenges that compete for a place in the outskirts of the city. In 2018, the PBL (Netherlands Environmental Assessment Agency) wrote about the many different spatial challenges that meet each other in the outskirts of the city. In addition to the classics such as housing, agriculture and nature development, think of water storage, mobility, the energy transition and recreation. 

All these tasks that are given a place means that things also have to disappear. In nine out of ten cases, this is agricultural land. This brings me to a little digression, because even socially, extensive analyses can be written about the outskirts of the city. What does it tell us that we call it 'urban periphery' and not, for example, 'rural periphery' or 'nature edge'? In any case, it shows that we mainly focus on the city and that we reason from there. 

To understand my thesis title 'Ecotone Urbanism', it is good to explain what the definition of 'ecotone' is. This is a border strip between different biotopes or landscapes. In general, a term that is mainly used within ecology to name transitions such as forest to heath or a bank between water and the shore. The transition from urban landscape to whatever landscape surrounds the city can therefore also be seen as an ecotonic. In my thesis, I looked at how we can urbanize this ecotone in a way that strengthens biodiversity. At first glance this seems like a contrast, or a contradiction, but nothing could be further from the truth. 

A striking fact is that various studies show that biodiversity in the urban periphery is in many cases higher than in the surrounding areas, both inside and outside urban areas. In addition, the biodiversity of many current agricultural areas is particularly low. In my thesis, I came to the conclusion that biodiversity can actually increase compared to the previous situation. With the caveat that biodiversity is increasing, but that the species in the area are changing (e.g. birds of prey and field mice are decreasing, songbirds and insects are increasing). In addition to increasing species populations and making them healthier, an increase in biodiversity also has positive effects on ecosystem services and increases the natural perspective and experience of city dwellers.

Figure 2: Robust green-blue public spaces, which are wide enough (30 m or more) that animals feel safe in the core of the area, with effective connections between other public green spaces or nature reserves, contribute the most to an increase in biodiversity. Use as much native vegetation as possible and ecological landscape structures such as hedgerows and ecological banks. 

In my thesis, I mainly looked at how public green spaces can be designed to strengthen biodiversity as much as possible. I did this based on principles from landscape ecology. Using the same ingredients (hectares of housing, infrastructure, water and public green spaces) for the expansion of a residential area, I created four variants in which the public green space had been given a different shape and interconnectedness. Based on three target species and expert judgement, the conclusion was that an urban ecotone could definitely mean an increase in biodiversity. In addition, there are also great opportunities to use the expansion of the residential area to strengthen current ecological connections or to create 'missing links' in an ecological connection zone. It is therefore always of great importance to connect the green structure of the expansion district to regional nature connections. 

Figure 3: The four different configurations of public green spaces in a new expansion district. All variants have the same number of hectares of public green space. A combination of green wedges with effective corridors came out best in the test based on expert judgement. 

One of the most important recommendations of my thesis was integral design, i.e. working together with other disciplines to achieve a more complete and richer design. In the case of biodiversity, the collaboration is of course with an ecologist. But in the field, I am finding out more and more that it is essential to work together with many different disciplines. In Wageningen at BLP/MLP, integral working and design is instilled in them from an early age. This made me assume that everyone knew and did that. But there I came home from the cold fair. I regularly see around me that there is too late or too little collaboration with other disciplines. This often results in missing out on great opportunities or better solutions. So stay aware that what you are learning now is not normal for everyone. 

At first glance, the outskirts of the city, the meeting between red and green, and my thesis topic, housing and biodiversity, seem to be a contrast. An extra insight into this subject showed me that it is not about contrast, but that city periphery are dynamic transition zones where connection and integrality are central. I propose that we are far from finished talking about the urban periphery, no longer as a contrast, but as a continuously dynamic landscape zone where the challenges of the future come together in integral design.



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