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  • D. Pataki

Is green infrastructure still experimental?

Many scientists have called for experiments to test the outcomes of green roofs, bioretention, and other nature-based alternatives to grey infrastructure. Does this mean that green infrastructure still needs more testing than grey infrastructure?


I recently had the opportunity to observe Melbourne's Green Our Rooftop project, a major green roof retrofit and demonstration project at the Department of Treasury and Finance. This project includes virtually all the elements that scientists want to see in green infrastructure (GI) implementation: there are scientific experiments built into the design, and research funding is available for data collection and post-occupancy monitoring that will inform future projects. Scientists from multiple disciplines and universities will observe or experiment with different parts of the green roof, which will be measured for its impacts on microclimate, building energy use, soil moisture, plant establishment, and biodiversity.


1 Treasury Place, the site of Melbourne's Green Our Rooftop project

For example, my University of Melbourne host Steve Livesley will measure the roof microclimate before and after construction, and our platypus-spotting colleague Nick Williams, who's a leading expert on green roof ecology, will test plant species suitable for Australian green roofs.


These are exactly the kinds of studies that many urban ecologists, including myself, have been calling for. I'd love for U.S. cities to take on more collaborative projects like this. But in thinking about what I and other scientists are asking cities to do, I've been weighing the pros and cons of emphasizing the experimental nature of GI. It's a truism that scientists virtually always want and need more data. But are we slowing the implementation of green solutions by continuing to paint them as less reliable, more uncertain, or less effective than grey infrastructure?


Experimental green roof at the Burnley campus of the University of Melbourne. This project has informed many green roof designs throughout Australia.

After some reflection and observations of local projects in Australia, I still find several good reasons to advocate for GI experiments in the rapidly growing implementation of nature-based solutions to urban environmental problems:


It's NOT just GI: there have been catastrophic failures of grey infrastructure


The need for GI has arisen out of the unexpected negative outcomes of building grey infrastructure across cities at huge scales. Aging pipes are leaking water, sewage, and methane in surprisingly large amounts. Impervious surfaces, storm sewers, and sewage treatment plants discharge too much water and pollution for natural waterways to handle. And our modern transportation system is the cause of many, many social, environmental, and health problems: vehicles crashes, traffic jams, air pollution, greenhouse gas emissions, hazardous waste, and more. Broadly speaking, our modern environmental crisis is largely a result of the current modes of urban, industrial, and transportation infrastructure. Given this, we really should have better tested their outcomes on smaller scales with the capacity to adapt when the negative consequences were apparent, but not yet as catastrophic.


Implementing any solution - nature-based or not - at large scales has the potential for unexpected outcomes when we don't fully understand the system we're working with. And modern cities are complex systems. The more we improve our understanding of how they work, the more we can minimize the chances of unanticipated problems down the road.


We're still learning how to successfully weave nature into modern industrial cities


Post-industrial cities are a relatively new phenomenon on the timescale of human knowledge, especially traditional knowledge. Ecologists like to say that urban nature is now made up of unique combinations of species and environmental conditions that may have no real analogue in natural ecosystems. If that's true (and this idea has been debated), then we may not be able to apply what we've learned from the study of natural ecosystems in urban contexts.


What's not debated is that we now import species from all over the world into cities. We also modify the environment in many ways, with increasing evidence that these changes are inadvertently affecting evolutionary processes.


All this is to say that nature is responding to urbanization in ways we don't yet fully understand. This is exemplified in the many modern cities that have a strongly colonial history, in which settlers from Europe or other regions built new cities and settlements with little historical or traditional knowledge about how to cope with local ecological and environmental conditions. This is one reason why indigenous ecological knowledge is so critical for nature-based solutions. And it highlights the need for thoughtful, evidence-based approaches for incorporating nature into cities in new (and old) ways.


GI must be designed with an understanding of ecological dynamics


One of the many ways that GI differs from grey infrastructure is that it's dynamic. Plants grow and die, species migrate and adapt, pollinators and other animals come and go, and microbes both compete with and promote the growth of other organisms in different ways over time. This can be a great asset and advantage of GI: unlike pipes and concrete, GI can regenerate itself. But it can also be unpredictable without a good understanding of how biological and ecological dynamics work.


Because we've largely ignored ecological processes for so long, we need to think about and do things differently to account for and build ecological dynamics into the function of streets and rooftops. This is very doable but it takes an adaptive approach: lessons from one project need to be quickly adapted into the next project. And the fastest way to build and transfer this knowledge is with sound experiments and strong collaborations between scientists and practitioners.


What do you think about the need for experiments in GI and nature-based solutions? Are the risks of green and grey infrastructure different? Is modern urban infrastructure inherently experimental? Leave a comment and let me know.

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