The Rise of Urban Vertical Forests

In 2014, the Bosco Verticale — Vertical Forest — opened in Milan, Italy. Designed by architect Stefano Boeri, the twin residential towers host more than 900 trees, 5,000 shrubs and 11,000 plants across their facades. The project was celebrated as a breakthrough in sustainable urban design, prompting architects, urban planners and environmentalists to reconsider how cities might integrate nature in ways that go beyond parks and street-side plantings.

The concept of incorporating vegetation into building exteriors is not entirely new. Green roofs — flat or sloping rooftops covered with plants — have existed for decades, and examples of climbing plants adorning the walls of old buildings are widespread in European cities. What distinguishes the vertical forest is the structural ambition of the undertaking: trees weighing up to 1.5 tonnes must be supported at significant heights, requiring specially designed cantilever beams and deep-rooted planting boxes. The engineering challenge is considerable, and the cost per planted tree is many times that of a conventional street tree.

Supporters argue that the benefits are manifold. The plants absorb carbon dioxide, reduce particulate matter, lower ambient temperatures around the building, and provide habitat for birds and insects. A study by the Polytechnic University of Milan estimated that the 8,900 square metres of plant-covered facade on Bosco Verticale produces an effect on microclimate equivalent to a conventional park of roughly 50,000 square metres. Residents report psychological benefits from living amid greenery, and the biodiversity on the towers has attracted over twenty species of birds to an otherwise dense urban area.

Critics, however, question whether vertical forests represent a genuine ecological advance or merely a form of expensive ecological theatre. The primary concern is maintenance. Unlike horizontal green roofs, vertical plantings are difficult and dangerous to access. Each tree must be individually tended by specialist arborists using industrial window-cleaning machinery. In Milan, this maintenance programme costs approximately €250,000 per year. Critics argue that equivalent ecological benefits could be achieved at a fraction of the cost by planting conventional urban greenery at ground level.

A further objection relates to the demographic of those who benefit. Vertical forests currently appear exclusively in luxury residential and commercial developments. The Bosco Verticale apartments sell for prices well above the Milan average, placing the ecological benefits — and the architectural prestige — firmly in the hands of wealthy inhabitants. Urban ecologists have noted that this premium positioning means the model is unlikely to be adopted in lower-income neighbourhoods where urban heat island effects and air quality problems are most acute.

Despite these criticisms, the model is spreading. Vertical forest projects are under construction or completed in cities including Nanjing, Lausanne, Eindhoven and Utrecht. Singapore has made biophilic urban design a national policy priority, mandating that new developments replace the greenery lost at ground level with equivalent planting elsewhere on or around the building. The question of whether vertical forests will remain an architectural luxury or become a mainstream urban infrastructure remains open.

What is not in doubt is that the interest they have generated has contributed to a broader cultural shift in how the relationship between the built environment and the natural world is conceived. Even critics who dispute the cost-effectiveness of vertical forests acknowledge that they have forced a serious conversation about the role of nature in dense urban settings — a conversation that parks and street trees alone were failing to provoke.

The Archaeology of Sleep

A. Sleep is often treated as a passive state — the absence of wakefulness. Yet the science of the last three decades has thoroughly dismantled this view. Sleep is now understood to be an active, biologically complex process during which the brain consolidates memories, clears metabolic waste products, regulates hormonal systems, and undergoes the neural maintenance that conscious life makes impossible. Understanding sleep has become one of the most productive frontiers in neuroscience.

B. Despite this scientific progress, the history of human sleep remains poorly understood. The dominant model, largely unchallenged until the late twentieth century, assumed that pre-industrial humans slept in a single consolidated block of seven to eight hours — interrupted only by illness, threat or noise. This assumption was so thoroughly embedded in medical literature that deviations from it were classified as pathological. Patients who woke in the middle of the night and could not return to sleep were diagnosed with sleep-maintenance insomnia and treated accordingly.

C. The historian A. Roger Ekirch challenged this consensus decisively in his 2001 paper and subsequent book "At Day's Close: Night in Times Past." Drawing on over five hundred pre-industrial historical sources — diaries, court records, medical texts, and literary works — Ekirch assembled compelling evidence that before the widespread adoption of artificial lighting, the typical human sleep pattern consisted of two distinct phases. People would sleep for three to four hours after nightfall, then wake for a period of one to two hours of quiet activity — prayer, reflection, conversation, or sexual intimacy — before returning to sleep until dawn. He termed these phases "first sleep" and "second sleep."

D. The implications of Ekirch's research were significant. If biphasic sleep was the human norm for most of recorded history, then the consolidated eight-hour sleep enforced by the industrial schedule might itself be an artefact of modernity — and the night-time waking that millions of people experience might not be a disorder at all, but a reversion to an ancestral pattern. Several sleep researchers found this hypothesis worth testing. Studies conducted in controlled environments without artificial light, most notably by psychiatrist Thomas Wehr in the 1990s, found that participants naturally reverted to a biphasic pattern within weeks.

E. The picture, however, is not straightforward. Cross-cultural studies of present-day hunter-gatherer societies — groups whose sleep patterns might offer the closest analogue to pre-agricultural human sleep — have produced more complicated findings. Research published in 2015 examined the sleep patterns of three groups: the Hadza of Tanzania, the San of Namibia, and the Tsimane of Bolivia. Contrary to popular assumption, none of these groups practised anything resembling the eight-hour consolidated sleep of the Western ideal, but neither did they universally exhibit the biphasic pattern Ekirch described. Average sleep duration was six to seven hours, fragmented but with no consistent mid-sleep waking period. Temperature appeared to be a stronger predictor of sleep timing than light exposure.

F. These findings suggest that the relationship between artificial light and sleep consolidation may be less deterministic than Ekirch's model implies. They do not disprove the existence of pre-industrial biphasic sleep in European populations — the historical sources remain — but they complicate any simple narrative of a single ancestral human sleep pattern disrupted by industrial modernity. Sleep, it appears, is shaped by culture, climate, technology, and individual variation in ways that resist easy generalisation.

G. What all sides of the debate agree on is that the medicalisation of sleep in the twentieth century — driven partly by the pharmaceutical industry's interest in sleep disorders — has imposed a normative ideal that may not accurately reflect human biological diversity. Recognising this diversity, researchers argue, is the first step towards more nuanced clinical approaches: ones that treat the full range of sleep patterns not as deviations from a fixed norm, but as variations within a much broader natural spectrum.

Rewilding and the Politics of Absence

The term "rewilding" entered mainstream ecological discourse in the 1990s, initially associated with the reintroduction of large predators to areas from which they had been extirpated. Its most celebrated early case was the reintroduction of grey wolves to Yellowstone National Park in 1995, after an absence of seventy years. The ecological outcomes were dramatic enough to generate a concept that would subsequently become one of the most debated in conservation biology: the trophic cascade.

Wolves, as apex predators, suppressed deer populations and changed their grazing behaviour. Deer avoided valleys and gorges where they were vulnerable to predation, allowing vegetation to recover in those areas. The recovered vegetation stabilised riverbanks, reducing erosion and altering the physical course of some waterways. The wolves, in other words, changed the rivers — a finding that captured public imagination and gave rewilding advocates a powerful narrative.

That narrative has since attracted significant scrutiny. Some ecologists have argued that the trophic cascade in Yellowstone was overstated, and that other factors — drought, changes in elk hunting by humans, and natural vegetation cycles — contributed substantially to the observed changes. The debate illustrates a persistent tension in rewilding science: the difficulty of isolating causal variables in complex ecological systems means that compelling stories can outrun the evidence supporting them.

The geographic scale of rewilding ambition has expanded considerably since Yellowstone. The European rewilding movement, represented most prominently by the organisation Rewilding Europe, advocates for the restoration of large, interconnected wilderness areas across the continent. This vision goes beyond predator reintroduction to encompass the removal of human management from large landscapes and the recovery of self-regulating ecosystems over time. In practical terms, this has meant converting marginal farmland — often abandoned as agricultural consolidation and rural depopulation have accelerated — into wildlife corridors and habitat patches.

The politics of such projects are rarely simple. Rewilding proposals frequently encounter opposition from farming communities who view the return of predators as a direct threat to livestock — a threat that is not imaginary. In Scotland, proposals to reintroduce lynx have been debated for years; proponents argue that lynx would control roe deer populations and cause minimal livestock losses, while opponents, particularly sheep farmers, remain unconvinced by proposed compensation schemes. Similar conflicts have played out across continental Europe as wolf populations have naturally expanded their range from refugia in Italy and the Balkans.

A less-discussed dimension of rewilding's politics concerns the human communities within proposed rewilding zones. The rhetoric of "letting nature take over" can carry an implicit assumption that human presence and ecological health are incompatible — an assumption with troubling resonances for rural communities facing economic decline. Critics from geography and social science have pointed out that the landscapes proposed for rewilding are not wilderness; they are cultural landscapes shaped by centuries of human activity, including pastoral farming that has itself created habitats valued by conservationists. The grasslands of the English uplands, for instance, support species assemblages that depend on continued grazing — removing that management would not produce "natural" habitat but a different, and not necessarily richer, ecology.

Proponents of rewilding are aware of these tensions and increasingly emphasise human co-existence rather than human absence. The concept of "compassionate rewilding" attempts to integrate the needs of local communities into restoration projects, recognising that durable conservation outcomes require local support. Whether this integration can be achieved without compromising the ecological ambition that defines rewilding at its most visionary remains an open question — one that will be answered not in academic papers, but in the negotiations between ecologists, farmers, planners, and politicians that constitute the actual practice of conservation.