DOZENS OF TALL, WOODEN structures have appeared in European cities in recent years. Their height and shape allude to a frequent function of columns in public squares — usually vents for building HVAC systems or subways. Peering through the wooden slats of these structures, however, doesn’t reveal steel grills expelling hot exhaust, but rather a lush moss surface running the height of the structure and releasing refreshing, clean air. This is CityTree, a unit developed by Germany’s Green City Solutions to filter and cool the air in dense urban environments.

“The CityTree is a combination of street furniture and biofilter — a bench at the bottom and a wooden ‘tower’ with our moss-filter technology inside,” says Simon Dierks, marketing lead of Green City Solutions. “Combined with sensors, intelligent ventilation, irrigation, and software, we make the natural ‘superpowers’ of moss usable and measurable and bring it to urban hotspots.”

The company has developed a specially cultivated moss to maximize “the outstanding natural ability of living moss to filter fine dust and cool the ambient air,” Dierks says. The company’s moss filters “can remove up to 82 percent of fine dust from the air and cool the air up to 4 degrees Celsius, measurably improving the air in the immediate environment.”

Green City Solutions has installed 30 CityTree units in cities including London, Berlin, and Munich. The success and measurable impact of its moss filters has led to additional products to naturally filter urban air, such as their latest CityBreeze units.

“While the CityTree with its bench works as a piece of street furniture,” says Dierks, “the CityBreeze combines the moss filter on one side with a large LCD screen on the other side.” The LCD screen can be used to display air quality data and be used for outdoor advertising, providing financial incentives for cities and public buildings to install them.

The company aims to show that their moss-based air filtering and cooling systems are “low-maintenance, long-lasting systems that rival conventional, engineered filters in terms of performance,” says Dierks. “Unlike conventional air filters, our products don’t produce any filter waste, as the mosses are never ‘full.’ We’re working with a circular approach.”

Nature-enabled infrastructure works with natural processes to mitigate climate change and clean and heal the urban environment.

Green City Solutions is one of a growing number of innovators changing the relationship between cities and nature by developing a new style of urban infrastructure. This nature-centric, nature-enabled infrastructure works with natural processes to mitigate climate change and clean and heal the urban environment. Instead of seeing infrastructure and its tons of cement, steel and carbon waste as the cost of making the urban machine run, designers are reimagining it as a living element of the city that works with nature, not against it.

Here are some other innovations that weave nature and natural processes into urban infrastructure, offering a vision for a path forward that increases the well-being of all a city’s citizens regardless of species.

IN THE CENTER OF BELGRADE, Serbia, a bench provides a resting area for pedestrians complete with lights and a phone charger. Nothing too unusual, apart from the chamber of green, glowing liquid bubbling at the back of the bench, and the engraved name at the top, “liquid3.”

liquid3 is a multifunctional bench that uses microalgae to remove carbon dioxide from the air, return clean oxygen into the atmosphere, and create an energy and nutrient-rich biomass in the process. The first bench was installed in the city last year as a local response to a local problem: Belgrade is situated close to two coal power plants that pollute the air with high levels of CO₂ and particulate matter, both of which are captured and filtered by liquid3.

The structure, which can be installed in one day and takes up only two square meters of space, provides the air-cleaning equivalent of one adult tree. As Dr. Ivan Spasojević, one of its creators, says, it is an “urban photo-bioreactor, aimed to supplement for trees in areas that do not allow traditional greenery” due to lack of space.

Its design weaves both environmental and public benefits into the structure. “liquid3 serves as a multifunctional urban mobiliary — bench, solar charger for phones and laptops, and nightlight,” says the team behind the project at University of Belgrade’s Institute for Multidisciplinary Research. A “LED light is positioned above the green micro-algal culture to induce relaxing effects. The construction has a slender vertical axis and ‘shelters’ the user from the street traffic to create a green oasis that enables relaxation and communication even during winter months.”

Even more than moss, microalgae are exceptional natural air-cleansing bio machines. They can thrive in environments inhospitable to most greenery, can absorb CO₂ ten times more effectively than trees, and when they get their fill of CO₂ the microalgae can be used to produce biofuel or as ingredients for a range of foods and consumer products.

So it’s no surprise that other urban innovators are turning to microalgae as well. When Cloud Collective had an opportunity to rethink how a motorway overpass bridge could function in Geneva, Switzerland, they too put microalgae to work. The Dutch-Flemish group created Culture Urbaine, a self-sufficient microalgae-growing unit that transformed a functional bridge into a feature-rich air-cleaning, biomass-producing system.

In the Culture Urbaine unit, a network of transparent tubes and solar panels attach to the bridge’s frame. A microalgae solution is pumped through the tubes, absorbing the CO₂ emitted by passing cars and expelling clean oxygen.

The citizens of Geneva now have an entirely new understanding of what an urban overpass can do in a city. For the collective, the project was a chance “to prove even these locations of highways and car dealers — despite their anonymous and generic character — can play an important role in the production of food and biomass.”

LONG BEFORE MOTORWAYS, cities relied on waterways to ferry industrial goods — and waste — away from their centers. Early on, the waterways’ wide banks and estuary ecosystems were replaced with cement walls and crude rerouting to meet the needs of urban industry. With the loss of the riverbanks and riverine ecosystems, the ability for waterways to filter pollutants and keep the water clean and healthy was also lost.

Scotland-based Biomatrix Water has developed “Floating Ecosystems” to restore the natural functions of lost urban riverbanks. The living modular flotillas act like water treatment plants and ecosystem support units, cleaning the water below and providing natural habitats and foraging sites for birds, bees, and smaller species above the water, as well as for fish below the surface.

“They are floating gardens usually planted with native plants, says Lisa Shaw, artistic director of Biomatrix Water. “They often look like a natural riverbank or small island but are usually in places where nature would struggle to take hold on its own, places where there are hard edged concrete or sheet pile banks that don’t allow for plants to grow naturally.”

Since 2012, 4,839 of these Floating Ecosystems have been used to help restore 153 bodies of water and waterways worldwide, including London’s Regent Canal, a historically blighted industrial waterway.

“There are butterflies, bees, bugs, moorhens, coots, and sparrows darting in and out and feeding from the plants,” reports Dave Bedford, co-chair of the Lower Regents Coalition, a community group in London working to restoring the canal. “If you look underneath the islands, you can see lots of fish sheltering. It looks beautiful and it is providing essential habitat for wildlife in the urban environment. It’s simply better on so many levels!”

“It is important to realize that nature-centric building is also building for the future.”

A growing body of scientific research shows how restored canals can also bring significant quality of life improvements to local residents. Researchers with Glasgow Caledonian University recently published data showing that people living within 700 meters of a restored canal experienced health benefits following restoration, including reduced risks of cardiovascular disease, hypertension, stroke, and diabetes.

While the floating ecosystems are designed to heal waterways, other urban innovators are looking to the bridges that pass over rivers and streams. That includes the Netherland’s NEXT Architects who designed the Vlotwateringbrug, popularly known as the “bat bridge,” in Westland, a municipality in the western Netherlands.

Westland recently implemented a landscape design scheme meant to create optimal conditions for insects and animals. When plans were made for a bridge to span one of the local waterways, it was discovered that the bridge’s location was in the middle of a flight route for numerous bat species, some of which are in steep decline due to loss of habitat. Another obstacle was the last thing at-risk bat species needed, so NEXT decided to pivot and approach the bridge as “a unique opportunity for a bat-friendly design.”

“The ecological requirements were not an additional feature to be added afterwards to the design,” said the firm in a report on the bridge. “Instead, they formed the backbone and the starting point for the bridge.”

The design team worked with bat experts from the Dutch Mammal Association to determine ideal features for bats that could be physically designed into the bridge. The result was a bridge built with an extra thick north side abutment to provide winter shelter for the bats, along with spaces at the bottom of the bridge and a custom brick balustrade to house bats during the summer. The roosting spaces under the bridge were designed to be wide enough to let bats in but narrow enough to keep predators out. No bat-friendly detail was overlooked — the edges of the roosting spaces were given a rough finish so the bats could grip their surfaces easily.

The bridge, says bat expert Marcel Schillemans from the Dutch Mammal Association, is “a textbook example of how a functional object can at the same time serve nature.” While bats have yet to populate the bridge, it was built as part of long-term strategy, “during which the surroundings change and also populations of bats change,” Schillemans says. “It is important to realize that nature-centric building is also building for the future, not only for immediate use by animals.”

OF ALL DIVISIONS between nature and the built environment, none are as defining as those between land and sea. Tons of cement and stone have been dumped along coastlines in the ultimate “us vs them” battle with nature. Long ignored, however, is the damage these sea walls have done to the “them” side of the equation, and how this damage has also made conditions worse for “us,” particularly as sea levels rise. At last, there is a growing understanding that a resilient future requires transforming barricades into bastions of life.

To that end, San Diego, California, recently installed an additional 1,000 feet of coastal protection along its shores to guard against rising sea water. Previously, large flat slabs of rock would have been used, which has often resulted in ecological dead zones for vulnerable shoreline species due to the lack of crevices, textures, and natural contours original coastal banks once offered.

To nurture coastal species and habitats, the city installed “Coastalock,” a new type of coastal barrier created by the company, ECOncrete, which contains shapes to mimic tide pool habitats and a specially textured surface to encourage the growth of plants and algae that help clean the water and provide nutrients to coastal species.

The barrier provides “sustainable pools for marine species to inhabit and rehabilitates those habitats for fish to enjoy cooler temperatures and organic living surfaces, while generating an expansive carbon sink in the process,” says ECOncrete on their website.

In Australia, Reef Design Lab and the Sydney Institute of Marine Science are working to re-establish aquatic habitats on existing seawall barricades by using custom-designed “habitat panels” to restore damage done to coastal areas during development.

“Many artificial marine structures such as seawalls, wharves, and pontoons are very different to natural shorelines such as rocky shores and mangroves,” says Aria Lee, who manages the project, labeled Living Seawalls. “This results in lower biodiversity and fewer native species inhabiting these artificial structures. Living Seawalls has developed an eco-engineering solution for enhancing marine life on new or existing seawalls. Modular habitat panels mimicking natural features — such as rock-pools, crevices, and hollows — are fitted to seawalls to increase habitat choice for marine life to boost biodiversity on artificial marine structures.”

Recent studies of the impact Living Seawalls have made in Sydney Harbor show that their designs “support at least 36 percent more species than plain, unmodified seawalls,” says Lee, with as many as 85 species of invertebrates, seaweeds, and fish living and growing on the panels, including vital water-cleansing species. “The increased surface area provided by our habitat-enhancement panels means more area for the native Sydney Rock Oyster to grow. These oysters are extremely efficient at filtering the water, so more oysters mean cleaner water for us to enjoy.”

Reef Design Lab has also developed its own vast portfolio of objects and systems to repair the damage done at the fault lines where humanity and marine life collide. Their “fish apartment” variation of habitat panels, for example, transformed the sleek below-water exterior of the Sydney Opera House into a welcoming shelter and breeding ground for the harbor’s sea life. The panels provide native species such as blue gropers and seahorses a place to hide from predators and re-establish their populations, which were decimated by dredging and development along the edges of Sydney Harbour.

In Victoria, Australia, Reef Design Lab is collaborating with Melbourne University’s National Centre for Coasts and Climate on a “hybrid coastal defense” project with a specially designed mangrove planter. Prior to coastal development and urbanization, the native southern mangrove species once served a vital role in protecting coastal areas there from erosion and coastal storms. The planters will help mangroves establish their root base, and, can be reused for further plantings once the trees have matured.

As urbanization increases while natural environments shrink and biodiversity decreases, this new approach to designing urban infrastructure holds the promise of a shift in the urban-nature divide. When nature is no longer seen as a force to guard against but an ally to join forces with, solutions such as these can help restore some balance to our built environments and support the non-human species with which we share space. And that can help us weather the environmental challenges to come.