In 2015 biologists in Singapore discovered something incredible: a flock of black swifts built nests on the 63rd floor of the CapitaGreen skyscraper, 280 meters above ground. It was the highest bird colony ever recorded in an urban environment. The birds didn’t just accidentally fly there — they chose the spot intentionally, because the whole city had been transformed into a gigantic vertical forest, specifically designed for wildlife to live between sky and ground.
A city-forest growing upward
Singapore is a tiny country roughly the size of Moscow within the MKAD ring road. Nearly 6 million people live here, but there is no space for conventional forests and parks. In 2009 the government launched the “City in a Garden” program, but with an unusual twist: instead of planting trees on the ground, scientists decided to grow forests on rooftops and building facades.
Architects, biologists and ecological engineers joined forces to create an interconnected system. Every new building was required to have “green terraces” — floors fully covered with living plants. But most interestingly, special “aerial bridges” for animals were constructed between buildings, covered with grasses and shrubs. These bridges connect buildings at heights of 20 to 70 stories, creating a continuous ecosystem in the sky.
How the vertical ecosystem works
Imagine a typical forest: grass grows at the bottom, shrubs above that, then trees, and birds live at the very top. Singaporean scientists recreated this structure vertically, using buildings instead of ground.
On the lower floors (1–10) shade-loving plants are planted: ferns, mosses, orchids. Insects, lizards and frogs live here. On the middle floors (11–30) shrubs and small trees grow, attracting butterflies and small birds. On the upper floors (31–70) plants tolerant of wind and strong sun are planted — this is where swifts and other high-flying birds settled.
Each plant was chosen deliberately. Biologists studied which species provide food (berries, nectar, seeds) at different times of year so animals can find food year-round. Engineers developed a special soil that is three times lighter than ordinary soil so buildings won’t collapse under the weight of trees. Irrigation systems collect rainwater and reuse it.
Scientific discoveries at altitude
Once the ecosystem was established, scientists began observing surprising things. Animals didn’t just move into the vertical forest — they changed their behavior.
Black swifts normally nest in cliffs at heights up to 100 meters. But in Singapore they rose three times higher. Ornithologists found that the birds learned to use upward flows of warm air from air conditioners to save energy while flying. They literally “ride” artificial air currents like invisible roller coasters.
Sailor butterflies (Papilionidae), which usually inhabit lowland jungles, adapted to life on the 40th floor. Researchers noticed their wings became slightly stronger — an evolutionary adaptation to stronger winds at altitude. This happened in just 15 years, incredibly fast for evolution.
The most unexpected discovery involved bees. Wild Tetragonula bees built hives on the 55th floor of the Oasia Hotel Downtown. Biologists found these bees fly up to 2 kilometers between buildings, pollinating plants at different heights. They effectively created a three-dimensional pollination network — instead of flying only horizontally like in a normal forest, they fly up and down between floors.
Numbers and facts about the vertical forest
| Indicator | Value |
|---|---|
| Number of buildings with green terraces | 247 |
| Total area of vertical gardens | 1.2 million square meters |
| Number of plant species | 2,847 |
| Number of animal species | 412 (birds, insects, reptiles) |
| Highest green terrace | 280 meters (63rd floor) |
| Length of aerial bridges for animals | 38 kilometers |
| Temperature reduction inside buildings | 3–5 degrees Celsius |
| Energy savings on air conditioning | 23% on average |
The interdisciplinary team
Creating the vertical forest required collaboration among specialists from many fields. Architects designed buildings taking into account plant weight and wind direction. Structural engineers calculated loads and built irrigation systems. Biologists selected plant species and monitored animals. Climatologists studied how green terraces affect city temperature.
Ethologists — specialists in animal behavior — played a special role. They observed how birds and insects used the aerial bridges and suggested improvements. For example, after ethologists noticed some birds were afraid to cross very open bridges, engineers added more shrubs for cover.
Even sociologists were involved. They studied how residents felt about living alongside wildlife. It turned out 87% of residents in buildings with green terraces reported reduced stress and improved mood.
New species in the city
After 15 years of the program, species that hadn’t been seen in the city for decades reappeared. Crested swifts, which disappeared in the 1990s due to deforestation, returned. Rare birdwing butterflies thought extinct in the region reappeared.
The most surprising was the arrival of Malayan colugo — a gliding mammal similar to a flying squirrel. These creatures glide between trees up to 100 meters. In Singapore’s vertical forest they learned to glide between buildings, using aerial bridges as “runways.” Biologists recorded a colugo’s glide from the 45th floor of one building to the 38th floor of a neighboring one — a record for the species.
Problems and solutions
Not everything went smoothly. The first problem was birds colliding with glass windows. Ornithologists recommended using special glass with ultraviolet patterns visible to birds but invisible to humans. Collisions dropped by 78%.
The second problem was invasive species. Some plants introduced for greening began to outcompete native species. Biologists created a “green patrol” — a team that regularly inspects terraces and removes unwanted plants.
The third problem was unexpected: too much success. As bird populations grew, so did droppings on balconies and windows. Engineers developed a system of “smart canopies” — special awnings that protect windows but don’t prevent birds from nesting.
Impact on the city’s climate
The vertical forest changed Singapore’s microclimate. Plants on buildings absorb solar heat and release moisture, cooling the air. Measurements showed that temperatures in areas with a high concentration of green buildings are 2–4 degrees lower than in areas with conventional buildings.
Plants also clean the air. One square meter of vertical garden absorbs about 130 grams of CO₂ per year and produces 100 grams of oxygen. Given 1.2 million square meters of green terraces, this is equivalent to the work of a 600-hectare forest.
| Environmental indicator | Before the program (2009) | After the program (2024) |
|---|---|---|
| Average city-center temperature | 32.1°C | 29.8°C |
| CO₂ concentration (ppm) | 445 | 412 |
| Number of days with an “urban heat island” | 287 | 156 |
| Biodiversity (number of species) | 1,847 | 3,214 |
Lessons for other cities
Singapore’s experience inspired other cities. Milan in Italy built two “Vertical Forest” towers (Bosco Verticale) with 900 trees on their facades. Paris plans to convert 100 hectares of roofs into green terraces by 2030. Even Moscow launched a pilot vertical greening project on several central buildings.
But Singapore remains the leader in scale and systematic approach. The main lesson scientists learned: a sustainable ecosystem requires not isolated green buildings but an interconnected network. Animals and plants need continuous “corridors” for movement, even if those corridors are 50 stories high.
The future of vertical ecosystems
Researchers continue to refine the concept. New projects include “vertical farms” — buildings where vegetables, fruits and even fish are grown on different floors in aquaponic systems. This allows the city to produce part of its food without using land.
Biologists are experimenting with creating full forest ecosystems at height. The idea is to recreate all levels of a tropical forest — from the forest floor to the canopy — but vertically, using building floors. The first such experiment began in 2023 in a 52-story building.
The most ambitious plan is to create “sky sanctuaries” for endangered species. Some animals, such as orangutans or rare birds, are losing habitat due to deforestation. Scientists propose creating special vertical habitats in cities where they can be protected and breed.
Significance for sustainable development
The story of Singapore’s vertical forest shows that cities and nature do not have to be enemies. With the right approach, buildings can become part of ecosystems rather than their destroyers. This is especially important because by 2050, 68% of the world’s population will live in cities.
An interdisciplinary approach proved key to success. When architects, biologists, engineers and sociologists work together from the start of a project, the result is far better than if each works separately. Buildings become not just places for people to live, but homes for hundreds of other species.
The swifts living on the 63rd floor are not just a curiosity. They are proof that nature is remarkably adaptable and can thrive even in the most unexpected places if we create the right conditions. Each of their nests in the clouds reminds us: the planet’s future depends on how creatively we can combine technology, science and respect for living things.
