The following text has been transcribed from the Creative Commons-licensed YouTube video directly above.

Andrew Gonzalez (Professor, Biodiversity Science, McGill University):

By 2050, 70 percent of the world’s 9 billion people will be living in cities. To meet that growth, we are gonna have to more than double urban infrastructure.

Urban Sustainability’s About Resilience

So cities are at the centre of our efforts to pivot society to a more sustainable footing, to meet the UN’s sustainable development goals. Today, I want to stress that urban sustainability’s about resilience, it’s the capacity of complex systems like cities to adapt and recover after unpredictable shocks.

Take, for example, the economic and the human impacts of flooding due to hurricanes or storms, or human deaths due to pollution or summer heat waves. In fact, cities are composed of ecological and social systems. Humans get many benefits from ecosystems embedded in cities. It’s those feedbacks between the ecological and the social that define the resilience of a city. We have to look to manage our cities from this perspective.

From here, it’s important to realize that as cities grow, urban development and roads dissect and bisect ecosystems. They reduce the total area of ecosystems, but it also hinders the flow of organisms, nutrients and energy between those ecosystems. That fragmentation erodes biological diversity, but it also erodes resilience.

The Erosion of Ecological Connectivity

Here is a map from Montreal that shows how high ecological connectivity, in red, has been eroded over the last 50 years. Patterns of urban sprawl like this are typical in cities all over the world, and they’re diminishing the contribution of ecosystems to urban resilience.

What I want to show you next is how to transform that pattern through time. What you see here is that pattern takes a form of a tipping point, a non-linear, negative relationship between ecological connectivity on the one hand and urban growth on the other. You see the sudden collapse like that, that’s typical of tipping points. And it’s very hard to slow, let alone reverse tipping points like this.

My research at McGill University has used theory, experiments in the lab and the field to show that when you disconnect ecosystems, you erode biodiversity and you erode resilience. But if you reconnect the ecosystem with links and critical nodes, you can recover resilience through time.

A Phone Call from the Government

In 2009, I received a remarkable phone call from the Quebec government. I was asked to use this research to design an ecological network for the city [Montreal] and its entire region. This was part of a broader strategy to improve the city’s resilience to ongoing climate change. You can imagine I was daunted by the scale of that request, but we rose to the challenge by forming a big team of researchers. We combined network science with different types of data on ecosystem quality and the movement abilities of different types of species. By combining this information, we could address the multiple dimensions of connectivity in the region.

So with this measure of ecological connectivity, we then combined projections from climate change models and land use change models to figure out how the connectivity of the city’s network would change into the future. Our algorithm calculates the impact of removing or deleting an ecosystem from the network. In this way, we could rank the contribution of every ecosystem to the connectivity of the whole system, which is needed for management and planning.

What I’m showing you here is a map of ecological connectivity for the region today. In dark green, you see the ecosystems that have high ecological connectivity, and in red and yellow, regions of low connectivity. So we can maintain connectivity by protecting those areas in green, but we can improve connectivity by restoring ecosystems in the zones in red and yellow.

Projections for 2050 (and Beyond) 

But what about the future? Here is a projection out to 2050. This is a business-as-usual scenario in which climate change and land use change have continued unchecked. Ecological connectivity has collapsed, in fact. We found that with scenarios like this, that we could maintain 75 percent of the region’s connectivity by protecting the top 17 percent of ecosystems.

Our algorithm and our model also allows us to identify fragments that contribute multiple benefits. Here you see, in light green, the forests within the city core that mitigate urban heat extremes, that provide urban cooling, but they also maintain biodiversity and carbon storage.

We’re working now with the city, with environmental NGOs, with business and the citizen groups to re-vision the city’s green belt as a living network. Constant engagement and communication in the planning and implementation has rapidly shifted the perception of the value of these ecosystems to the city as a whole. That’s a fantastic outcome of the research.

We’re working now with the city, with environmental NGOs, with businesses and the citizen groups to re-vision the city’s green belt as a living network. Constant engagement and communication in the planning and implementation process has rapidly shifted the perception of the value of these ecosystems to the city as a whole. That’s a fantastic outcome of the research.

It’s Applicable to Any City

This science can be applied to any city in the world. I’m excited to be here with you today to figure out how we might go about doing that. Urban ecosystems provide so many benefits to human populations, but managing urban ecosystems as a network will ensure and restore the resilience we need for that sustainable future that we’re all aiming for.

Thank you very much.