Have you ever noticed a certain similarity in public parks and back gardens in the cities of the West? A ubiquitous woodland mix of lawn grasses and trees has found its way throughout Europe and the United States, and it’s now spread to other cities around the world. As ecologist Peter Groffman has noted, it's increasingly difficult to tell one suburb apart from another, even when they're located in vastly different climates such as Phoenix, Arizona, or Boston in the much chillier north-east of the US. And why do parks in New Zealand often feature the same species of trees that grow on the other side of the world in the UK?
Inspired by the English and New England countrysides, early landscape architects of the 19th Century such as Andrew Jackson Downing and Frederick Law Olmstead created an aesthetic for urban public and private open space that persists to this day. But in the 21st Century, urban green space is tasked with doing far more than simply providing aesthetic appeal. From natural systems to deal with surface water run-off and pollution to green corridors to increasing interest in urban food production, the urban parks of the future will be designed and engineered for functionality as well as for beauty.
Imagine travelling among the cities of the mid-21st Century and finding a unique set of urban landscapes that capture local beauty, natural and cultural history, and the environmental context. They are tuned to their locality, and diverse within as well as across cities. There are patches that provide shade and cooling, places of local food production, and corridors that connect both residents and wildlife to the surrounding native environment. Their functions are measured and monitored to meet the unique needs of each city for food production, water use, nutrient recycling, and habitat. No two green spaces are quite the same.
Planners are already starting to work towards this vision. And if this movement has a buzzword it is “hyperfunctionality” – designs which provide multiple uses in a confined space, and a term coined by Richard Pouyat of the US Forest Service. At the moment, urban landscapes are highly managed and limited in their spatial extent. Even the "green" cities of the future will contain extensive areas of buildings, roads, railways, and other built structures. These future cities are likely to contain a higher proportion of green cover than the cities of today, with an increasing focus on planting on roofs, vertical walls, and formerly impervious surfaces like car parks. But built environments will still be ever-present in dense megacities. We can greatly enhance the utility of green space through designs that provide a range of different uses in a confined space. A hyperfunctional planting, for example, might be designed to provide food, shade, wildlife habitat, and pollution removal all in the same garden with the right choice of plants, configurations, and management practices.
Need for 'xeriscaping'
What this means is that we have to maximise the benefits and uses of urban parks, while minimising the costs of building and maintaining them. Currently, green space and street plantings are relatively similar throughout the Western world, regardless of differences in local climate, geography, and natural history. Even desert cities feature the same sizable street trees and well-watered and well-fertilized lawns that you might see in more temperate climes. The movement to reduce the resources and water requirements of such urban landscapes in these arid areas is called "xeriscaping" – a concept that has so-far received mixed responses in terms of public acceptance. Scott Yabiku and colleagues at the Central Arizona Phoenix project showed that newcomers to the desert embrace xeriscaping more than long-time residents, who are more likely to prefer the well-watered aesthetic. In part, this may be because xeriscaping is justified more by reducing landscaping costs – in this case water costs – than by providing desired benefits like recreation, pollution mitigation, and cultural value. From this perspective, xeriscaping can seem more like a compromise than an asset.
But there is other ways to make our parks and natural spaces do more. Nan Ellin, of the Ecological Planning Center in the US, advocates an asset-based approach to urbanism. Instead of envisioning cities in terms what they can't have, ecological planners are beginning to frame the discussion of future cities in terms of what they do have - their natural and cultural assets. In Utah’s Salt Lake City, instead of couching environmental planning as an issue of resource scarcity, the future park is described as "mountain urbanism" and the strong association of local residents with the natural environment of the mountain ranges near their home. From this starting point, the local climate, vegetation, patterns of rain and snowfall, and mountain topography are all deemed natural assets that create a new perspective when it comes to creating urban green space. In Cairns, Australia, the local master plan embraces "tropical urbanism" that conveys a sense of place through landscaping features, while also providing important functions such as shading and cooling in this tropical climate.
The globally homogenised landscape aesthetic – which sees parks from Boston to Brisbane looking worryingly similar – will diminish in importance as future urban green space will be attuned to local values and cultural perceptions of beauty. This will lead to a far greater diversity of urban landscape designs than are apparent today. Already, we are seeing new purposes for urban landscaping that are transforming the 20th century woodland park into bioswales – plantings designed to filter stormwater – green roofs, wildlife corridors, and urban food gardens. However, until recently we have been lacking the datasets and science-based specifications for designs that work to serve all of these purposes at once.
Stephanie Pincetl, the director of the California Center for Sustainable Communities, has described a new trend in urban infrastructure design. In the 20th Century, "grey" infrastructure made of concrete and other man-made materials was intended to safeguard public health by transporting waste out of crowded cities. In the 21st Century, we are seeing a shift toward "green" infrastructure which is focused on more sustainable outcomes. Grey infrastructure – pipes, lined canals and sewage treatment facilities – have very specific roles in order to meet precise guidelines for flows and pollutant concentrations. But more flexible, sustainable systems could also be built that could also carry out these highly specific tasks. New technologies for treating wastewater for example, look less like industrial treatment plants and more like ecosystems; the Port of Portland headquarters in Oregon uses a “Living Machine” to treat and reuse its wastewater using a simulated tidal wetland.
Windy city park
In Finland, Heiki Setälä of the University of Helsinki has monitored the urban environment to measure pollutant concentrations near tree canopies and in waterways. In New York City, Thomas Whitlow of Cornell University sends students through tree-lined streets with portable, backpack-mounted air quality monitors. At home in his laboratory, he places tree branches in wind tunnels to measure pollution deposition onto leaves. It turns out that currently, many street tree plantings are ineffective at removing air pollutants, and instead may trap pollutants near the ground. My students and I equipped street trees with sensors in and around the trunk in Los Angeles to monitor growth and water use in real time to help find which species provide the largest canopies for the lowest amount of water. Rather than relying on assumptions about the role of urban vegetation in improving the environment and health, future landscaping designs will be engineered based on empirical data and state of the art of simulations.
New datasets on the performance of urban landscapes are changing our view of what future urban parks will look like and what it will do. With precise measurements of pollutant uptake, water use, plant growth rates, and greenhouse gas emissions, we are better and better able to design landscapes that require less intensive management and are less costly, while providing more social and environmental uses. Alex Felson’s “designed experiments” in collaboration with New York City are a good example of this. Critically, there is a growing effort to understand the many and complex roles of urban green space in influencing human health and well-being beyond their effect on the physical environment alone. In 2012, a consortium of social scientists in the US carried out surveys in six cities, followed by interviews and questionnaires about biodiversity with individual households. These studies are helping both researchers and ecologists understand what kind of landscapes people want in different cities, so that future landscape designs can meet aesthetic and cultural as well as environmental needs. In other words, the hyperfunctional landscapes of the future will be beautiful as well as useful.
As the environment changes and the urban landscape evolves, so to must the design of the parks of the future. These urban landscapes will be as dynamic and diverse as their residents, wherever they may be.