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In the second half of the 21st century, the first living city was established in urban forest around Portland, Oregon. Sequoia City comprised a grove of 40 trees, including a hospital tree, schools, farms and recreation facilities (zip lines, slides and altitude swings). As they grew, residential trees eventually each housed dozens of families, living in custom-grown rooms made of living plant tissue. Children raised in Sequoia City saw no distinction between humans and other lifeforms. To them, ecology – the study of life in relation to its environment – was something they understood in their bones. That they were connected to nature went without saying; their intimacy was innate.

Sequoia City was a demonstration settlement, established to provide the proven mental health benefits of living in nature, to support the storage of carbon in living trees and soils and to tackle the extinction crisis.

It was inspired by ecologists who had discovered other species that had domesticated plants to live in. Philidris ants in Fiji sow seeds of Squamellaria on the branches of large trees. The ants tend the seedlings, which, as they grow, form large, hollow structures called domatia. The ants are saved the effort of building a nest and move into the domatia. The Squamellaria produce fruit too, which the ants eat. Descendant ants plant more seeds taken from their crop and the symbiotic cycle carries on.

The planners behind Sequoia City saw what the ants were doing and thought it looked like a good idea. Inspiration also came from living tree cities in science fiction, such as Cixin Liu’s Remembrance of Earth’s Past trilogy.

Giant sequoia are some of the largest organisms to have existed on our planet. They can live for up to 3000 years and grow up to 90 metres tall. In the early 21st century, their numbers fell in their native range in the Sierra Nevada mountains of California due to the climate crisis, but they continued to grow well in wetter, more northerly regions such as northern Europe and the Pacific Northwest. Oregon was chosen as the first location for a living city.

There were a few problems to overcome in developing the residential trees. The biggest was the slow growth of sequoias. Although faster-growing than the likes of oak, sequoia still take at least 100 years before they are big enough to live in.

However, the was well known, and our understanding of the genetics of plant growth was sophisticated enough even back in the 2020s to locate genes related to fast growth. With careful gene editing, it was possible to create sequoia that develop ultra rapidly. The key DNA sequences came from eucalyptus, one of the fastest growing trees, and bamboo, which, despite being a grass not a tree, supplied some important traits that enabled the development of a suitable species of sequoia.

The resulting trees formed their own version of domatia, encouraged by inserting guiding bars into the plant tissue. Different sized rooms could easily be grown, and windows installed. Bathrooms and toilet facilities were fully plumbed. Sewage was processed by specialised microbes and recycled into soil at the base of the tree and in the numerous gardens high in the tree itself.

Epiphytes – plants growing on other plants – are . In Sequoia City, garden zones and farm zones grew a range of squashes, cereals and beans, which the residents both consume and trade. Small cherry and apple trees themselves grew in orchard zones supported by the giant sequoia. Water farms on the trees deployed bromeliads, ferns and mosses to trap moisture from the air and send it down pipes to storage domatia. Electricity was supplied by wind and solar installations on individual domatia and on specialised power trees.

The success of Sequoia City spawned a series of copies around the world that used gene-edited species native to their region: Oak City and BeechTown in the UK, Bamboo MegaCity in southern China and Gum Towns, made of eucalyptus, in Tasmania and New South Wales in Australia. The domestication of the baobab and its subsequent gene-editing for accommodation led to spectacular Baobab towns in Ghana, Kenya and Sudan. By the end of the 21st century, satellite surveys of tree cover confirmed a significant fraction of previously deforested land had been regreened, and estimates suggested that the tree cities had contributed to a large reduction in atmospheric carbon dioxide. Studies reported that species diversity and population sizes had returned to levels not seen since the 19th century.

Tree children, immersed in the arboreal high life, traditionally got their first pair of wings – modified hang gliders – at age 10.

Invention

Living-tree homes

Time stamp

2070

Tagline

The ultimate in eco-living

Future Chronicles explores an imagined history of inventions and developments yet to come. Rowan Hooper is the podcast editor at New Scientist and author of How to Spend a Trillion Dollars: The 10 global problems we can actually fix.