Delft University of Technology (TU Delft) is one of the knowledge partners on GreenDense, providing the latest insights from their extensive research into what it really takes to make nature thrive in a city. As part of the project, TU Delft has supported partner cities through urban diagnosis mapping, student-led design research, and the development of the GreenDense Pattern Atlas - an open, evolving resource that helps cities identify the right greening strategies for their specific contexts. We spoke to TU Delft's Nico Tillie, associate professor at the university's Urban Ecology Design Lab, about the organisation's role on GreenDense, the thinking behind the Pattern Atlas, and what makes him hopeful about the future of urban greening.
Nico thinks about urban ecology on an expansive scale. Plastic particles, as he points out, have been found on the summit of Mount Everest and in the deepest parts of the ocean. There is, in other words, no truly natural environment left on earth untouched by human activity. "The construct of urbanism has become global," he says. "So we don't really distinguish anymore. It's all anthropogenic ecology." With this opening introduction to his work, Nico set the tone for the holistic lens he and the team at TU Delft apply to the urban greening projects they work on, including GreenDense.
Designing urban nature around place and people
For Nico, successful urban greening depends on combining TU Delft’s design research with expertise in ecological maintenance and stakeholder engagement. Within GreenDense, TU Delft’s design research complements knowledge partner Plante & Cité’s expertise in the long-term maintenance of urban greening sites, alongside the stakeholder-engagement perspective originally contributed by former partner STIPO.
“Nature-based solutions is a term that’s too often used as a trick,” he says. “You take something that worked in location A and drop it in location B - different country, different culture, different relationship with the land - and it doesn’t always work.” His preferred framing, particularly outside city contexts, is landscape-based solutions: approaches that begin with who lives somewhere, how they use the space and what they actually want from it. “It’s biodiversity, yes, but it’s also biocultural diversity. That tailor-made quality is what makes things last.”
This context-sensitive approach is central to GreenDense: rather than applying standard solutions, the project helps cities connect ecological ambitions with the physical characteristics of a site, the practicalities of maintaining it and the needs of the people who use it.
Showing cities what's possible
Sometimes the most valuable thing an outside perspective can offer is simply a higher ceiling. Last year, Nico had two master's students focused on the GreenDense project. One worked with the GreenDense partner city of Bruges, where the city's conservation-minded mayor had long insisted that heritage aesthetics - cobblestones, medieval character, specific colours - took priority, leaving little room for the greening team to be ambitious. When the student began mapping what was actually possible in a particular street, the conversation shifted.
"In the first workshop, they talked about wanting green in that street," Nico recalls. But when the team asked what their specific ambitions were in terms of additional green space they started talking about a mere six square metres of additional greenery. The research student working on this project took this as a challenge. Through detailed drawings and calculations, she showed what that same street could look like with a full rain garden treatment - trees, shrubs, water storage - and the ambition jumped from six square metres to fifty or a hundred. Another of Nico’s research students worked with the GreenDense partner city of Mechelen, taking a more analytical approach that mapped the city's historical growth to identify targeted intervention points - what Nico calls "green acupuncture" for heat stress and biodiversity gaps.
In both cases, the work fed directly back into the cities' own planning processes - which is, Nico says, exactly the point. "Research should not sit in a drawer. It should have an effect outside."
How the Pattern Atlas will help urban greening practitioners
The most substantial knowledge output TU Delft is bringing to GreenDense is the Pattern Atlas, developed primarily by PhD candidate Jacques - an architect who has already published two books on urban nature and is now using the six GreenDense cities as a testing ground for a broader design methodology.
The atlas works as a kind of decision-making map for cities. On one side are ecosystem services - what a city wants to improve, whether that is biodiversity, water management, heat reduction, or the quality of public life. On the other are urban morphology types: the alley, the through road, the square, the access road, the building. Because every European city has these elements regardless of national planning tradition, they provide a common language that does not rely on country-specific typologies. Between the two sits the solution: a pattern that links a spatial context to a problem to an outcome.
"The idea is: you are a city, you have this problem in this kind of space, and the atlas maps your journey to a solution," Nico explains. But he is careful to resist the idea of it as a fixed toolkit. "If you have a hammer, every problem looks like a nail. The atlas is not like that. New patterns are being added all the time as new challenges emerge."
He gives the example of an eco-ridge: when a channel is dug beside a road to collect rainwater, the leftover soil can be piled up alongside it and shaped to create habitat for ground-nesting bees or, if the bank is made steeper, birds such as kingfishers.
The atlas is currently being finalised and should be ready within the coming months, at which point it will be openly available to city practitioners, urban designers, and anyone else working to bring more nature into dense urban environments.
Towards a GreenDense Academy
The next step is what the project is calling a GreenDense Academy: a way of combining the Pattern Atlas with Plante & Cité's maintenance knowledge and the stakeholder engagement tools developed with STIPO, so that cities can make practical use of the insights provided by all three. Bruges has already shown this is possible, running its own workshops based on the student's strategies without TU Delft's direct involvement. "That is what research should do," Nico says. "Not sit in a drawer. Not just be published online. It should have an effect outside."
The GreenDense Academy will be piloted with the GreenDense cities before the project closes, with the goal of making it transferable - something other cities across Europe can pick up and use independently.
Reasons to be hopeful
Nico is clear-eyed about the obstacles that stand between urban greening ambitions and the current reality: political will that shifts with each election cycle, city departments constrained by their briefs, the sheer gap between what urban greening researchers envision and what overstretched city teams feel able to attempt. But when asked what gives him hope, his answer is clear.
"The students," he says. "They come in with energy and ambition and they show what is possible. And often that is exactly what a city needs - someone from the outside to say: look, this is what could be here."
We look forward to continuing to share this hope with followers of the GreenDense project as it enters its final year. Stay tuned for news of the Pattern Atlas and GreenDense Academy, coming soon!