Trees and the city
For a large portion of humanity, everyday contact with nature is restricted to the green spaces found in and around urban areas: house gardens, public parks or tree-lined streets. When they exist, they are usually described as “oasis” and cherished as places of leisure, refuge and coming together.
Unfortunately, many urban development models tend to focus on man-made infrastructure and a “taming of Nature”. A mix of technical preferences, economic considerations and public regulations gives priority to paved and built areas. Trees and other plants are usually handled as ornamental or utilitarian elements, from a human perspective. Limited to areas as small, convenient and safe as possible, these green spaces become disconnected, like islands in the city’s landscape, and without room to evolve, foster diversity and provide other valuable services. Fortunately, this paradigm is changing.
In 1950, there were 750 million people living in urban areas around the world, according to data collated by the UN’s Population Division. In 2018, this number had exploded to 4.2 billion – about 55% of the global population – and kept on growing. 1,8 billion people lived in cities with more than 1million inhabitants and, in most developed countries, 80% of the population was classified as urban.
Urbanisation and Nature
Modern cities are complex entities with a significant footprint. As they grow, they replace existing ecosystems with multiple layers of built infrastructure, cutting the normal interactions between above and below the surface. To function, cities depend on a continuous flow of food, energy and materials from all over the world; in exchange, they generate a continuous stream of residues that need to go somewhere else. According to a 2011 report from the UN Habitat Initiative, reviewed here, cities occupied 2% of the global land area and consumed roughly 75% of all natural resources.
Given the numbers above, urbanisation creates both a local and a global impact on biodiversity and ecosystem services. This makes the fate – and shape – of nature tightly intertwined with the future of cities, and vice-versa.
Adapting to a changing world
When the UN introduced the Sustainable Development Goals in 2015, Goal 11 was explicitly dedicated to cities. The influence of natural factors is patent in several targets and indicators of this goal, as are the links to other SDGs related to the environment.
On their own, the SDGs have helped to launch or reframe several initiatives for more sustainable cities, energising public participation, research, politics and business towards new directions. This transition has been made more urgent by climate change and the ever-growing list of extreme events, such as the recent heatwaves and record-breaking temperatures sweeping the northern hemisphere. Almost simultaneously, these have affected hundreds of millions of people in cities across Europe, North America and Asia, showing how vulnerable cities are to changes in their normal conditions.
Recognizing these serious challenges, many governments around the world have been planning to make cities more climate resilient, in order to safeguard their citizens, infrastructure and essential economic activities. It is not an easy task, given the complexity of cities and the many functions they need to ensure but, as illustrated in this piece by the Guardian, it’s an opportunity to fulfil both new visions and old aspirations.
For those interested in a more in-depth view of different measures and examples from different parts of the world, we recommend this action-oriented report by McKinsey and the C40 Cities Climate Leadership and this comprehensive article at The Lancet. Another good source of information on policies and concrete options is the European Climate Adaptation Platform Climate-ADAPT, a partnership between the European Commission and the European Environment Agency, which also published this report on adaptation back in 2012.
Green infrastructure and urban forests
Nature-based solutions are given a key role in all these documents and initiatives, and is now accepted that they should be used to either replace or enhance built infrastructure, both in cities and in the broader metropolitan areas surrounding them. By creating green corridors, greening surfaces and buildings, restoring waterways and surrounding forests (or coastal mangroves) – the thinking goes – we can use ecosystem services that are cheaper, more flexible and more resilient than single-purpose technical solutions. In addition, these solution improve (and regenerate) themselves over time, besides helping to restore biodiversity and soak up carbon from the atmosphere.
Since urban planning is a very technical affair, it’s no surprise that planners and decision-makers think of these solutions as green infrastructure. Given the link with urban water management, another hot topic for cities, these are usually integrated as green & blue infrastructure. As this post at The Conversation highlights, there is also a link into circular economy and turning a problem into a valuable resource – like turning excess rainwater, which overloads public networks, into much needed freshwater. Assessing how this transition can be done from a technical and political perspective requires many different participants and a lot of hard data, as detailed by the American Association of Landscape Architects (ASLA) or in this more academic paper on climate adaptation. Coming from the accounting & consultancy side, Deloitte released a report on the Green Planning of Public Spaces. that covers the cultural, economic and environmental services of green spaces.
In this transition, it is also crucial to change the legal frameworks that define the uses of public and private spaces: public regulations and building codes have to be changed, to ensure that trees can be planted and cared for correctly (by the town or the communities), or that wilder green areas are legally acceptable. Since it’s important to win over the hearts and minds of the taxpayers and voters, communication with the broader public often replaces “green infrastructure” with “urban forests” – a slightly more inspiring way of referring to the collection of trees and shrubs that exist in an urban area. The initiative Cities4Forests, which provides a rather good reference guide, goes a step further and tries to make city governments look at urban, nearby and faraway forests as a necessary continuum. Their website shows several examples amongst their current 82 member cities and is well worth reading.
The times they are a-changing
The challenge is huge but it’s positive to see that many cities around the world are changing, making an effort to communicate with their citizens and inspire a long-term view. Given the different types of stakeholders, it is interesting to see how differently this is formulated by different organisations and professional groups:
- Public awards have a long tradition, as a way to recognise great examples and inspire others. To prove the point, we suggest looking at the AIPH World Green City Awards, the Green Cities Europe Award or the Green Flag Award. Any of these organisations provides a wealth of information for different types of audiences and support several initiatives. The Ashden Awards, though broader in their focus, are also a prestigious reference.
- Rankings are another way to get a sense of where we – and the others – are. The IS Global Global Ranking of Cities looked at 1’000 european cities and the link between green spaces and public health. As their short summary shows, it’s important to remember that greening measures also improve the quality of life and public health of cities.
- Looking at a few examples in the USA: the city of Atlanta provides a nice, if traditional, listing of all the benefits ensured by trees, while Philadelphia launched Cities Alive, a conference & trade show devoted to green infrastructure and related businesses. American Forests, an NGO, makes the case for both business and social equity (presented as “Tree Equity”) for the 60 million ha (!) of urban forests across the country. Crucially, the intersection with social issues is becoming a powerful driver for greener cities, particularly in how how green infrastructure links with wealth and health inequality issues. We suggest watching Vox‘s video about the city of Memphis, one of the hottest ones in the US.
- Across the pond, the District of Islington, in London UK, has created an attractive interactive map that shows the economic value and other benefits from their urban forest, as a way to inform and gather public support for further changes. Another map of London that features green spaces as a public service is that of the Cool Spaces Initiative, launched by The City of London in light of reoccurring heatwaves.
- The Landscape Institute, a professional body for UK’s landscape practitioners, shows several case studies for different types of urban settings, from residential to industrial sizes, in a way that is helpful for architects and planners. In the USA, the ASLA mentioned above fulfills a similar role of informing professionals.
- Going past the city boundaries, the Green Belt Initiative in Canada makes the economic case for the restoration of the natural infrastructure around the city of Ontario. Such initiatives are important, partly because of the methodology, partly because those numbers really help to drive the message home.
All in all, people seem to appreciate and benefit from having more green around them, and many cities are embracing the change. Our intro video, about the greening of Medellin in Colombia, provides an eloquent example of how powerful this change can be. The “green islands” we mentioned in the beginning are now being linked, to form green corridors that affect the city’s climate in a positive way while bringing other important benefits, from improved social interactions to increased real-estate values.
Recommended readings, for the summer break
- Guidelines on urban and peri-urban forestry. Prepared by the FAO in 2016, it distills the interactions from scientists, practitioners and public administrators from cities worldwide (link to PDF, 172 pages, English).
- Urban Forests: A Climate Adaptation Guide. This report, prepared by the Forest Service of the USDA, “presents information and ideas for optimizing the climate and human health outcomes of urban forestry projects and provides professionals who are working at the intersection of climate, public health, and urban forestry with resources to support climate adaptation planning and activities” (link to summary page, with PDF download link)
