Clip source: Promoting health and wellbeing through urban forests – Introducing the 3-30-300 rule | IUCN Urban Alliance

Promoting health and wellbeing through urban forests – Introducing the 3-30-300 rule

(This article was written by Prof. Cecil Konijnendijk van den Bosch and originally published on LinkedIn on 19 February 2021)

Urban forests provide a wide range of essential benefits. Current global challenges, such as climate change, environmental degradation, and the COVID-19 pandemic, have resulted in increased awareness of the importance of urban trees and green spaces. When working with cities, national governments, and international organisations, I am often asked for specific guidelines for developing successful urban forestry programs. I have mostly declined, because every city is different, which makes it difficult to set transferable targets across various contexts and settings for e.g., urban tree canopy cover.

However, the current state of research and practice, the urgency to green our cities and neighbourhoods, and the call for guidance from decision makers have made me to reconsider. While situations will always be complex and different, and guidelines are not written in stones, I would like to argue for a new rule of thumb for urban forestry and urban greening: the 3-30-300 rule. This rule focuses on the crucial contributions of urban forests and other urban nature to our health and wellbeing. It also recognises that we have to consider many different aspects of the urban forest in order to be successful. It also addresses the need for urban forests to percolate into our living environments. At the same time, it is straightforward to implement and monitor.

3 trees from every home

The first rule is that every citizen should be able to see at least three trees (of a decent size) from their home. Recent research demonstrates the importance of nearby, especially visible, green for mental health and wellbeing. During the COVID-19 pandemic, people have often been bound to their homes or direct neighbourhoods, placing even greater importance on nearby trees and other green in gardens and along streets. The Danish municipality of Frederiksberg has a tree policy that calls for every citizen to see at least one tree from their house or apartment. We should take this one step further.

30 percent tree canopy cover in every neighbourhood

Studies have shown an association between urban forest canopy and, for example, cooling, better microclimates, mental and physical health, and possibly also reducing air pollution and noise. By creating more leafy neighbourhoods, we also encourage people to spend more time outdoors and to interact with their neighbourhoods (which in turn promotes social health). Many of the most ambitious cities in the world in terms of greening, including Barcelona, Bristol, Canberra, Seattle, and Vancouver, have set a target of achieving 30% canopy cover. At the neighbourhood level, 30 percent should be a minimum, where cities should strive for even higher canopy cover when possible. Where it is difficult for trees to grown and thrive, e.g. in arid climates, the target should be 30% of vegetation.

300 metres from the nearest park or green space

Many studies have highlighted the importance of proximity and easy access to high-quality green space that can be used for recreation. A safe 5-minute walk or 10-minute stroll is often mentioned. The European Regional Office of the World Health Organization recommends a maximum distance of 300 metres to the nearest green space (of at least 1 hectare). This encourages the recreational use of green space with impacts on both physical and mental health. Of course it will be important to work with local context, as the needs in e.g., lower-density suburban areas will be different from those in denser urban areas. But also here efforts need to be made to provide access to high-quality urban green space, e.g., in the form of linear green spaces that double as cycle corridors and walking paths.

Applying the 3-30-300 rule will improve and expand the local urban forest in many cities, and with that promote health, wellbeing, and resilience.

About the author: Professor Cecil Konijnendijk van den Bosch is the Director of the Nature Based Solutions Instituteand Program Director (Master of Urban Forestry Leadership) at the University of British Columbia.

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The lead palaeontologist “celebrated his eureka by kindling a fire with 45-million-year-old twigs and boiling water for tea time,” writes historian Jared Farmer in Elderflora, his expansive global history of grand and venerable trees. Granted, these plants had been dead since the Eocene epoch. Nevertheless, as the author describes, the incident is part of a troubling pattern in which scientists rejoice at their discovery of the ‘oldest’ tree of their time — and then destroy it.

In 1957, for example, Edmund Schulman at the University of Arizona in Tucson spent the summer seeking ancient bristlecone pines in California’s White Mountains. He found three more than 4,000 years old, and named them Alpha, Beta and Gamma. Then, in the interests of tree-ring science, he chose to “sacrifice” Alpha, taking snapshots as his nephew and a colleague sawed it down. When the University of Arizona issued a press release titled ‘UA Finds Oldest Living Thing’, Farmer writes, “they say nothing about the thing being dead”.

Schulman’s aim was dendroclimatology — the reconstruction of climates using tree-ring data. That lofty motive cannot be ascribed to those who, in 1881, bored a tunnel into the 2,000-year-old Wawona tree in Yosemite National Park, allowing tourists to drive their cars through the 71.3-metre-high giant sequoia (Sequoiadendron giganteum), since toppled.

Arboreal legends
As Elderflora shows, big, old trees are objects of veneration and vandalism, appearing “in the oldest surviving mythologies and the earliest extant texts”. They were associated with gods and heroes, prophets and gurus: they had pivotal roles in the Mesopotamian Epic of Gilgamesh and in the Polynesian legend of Rātā, who fells a noble tree to carve a canoe. In more recent times, European settlers “dispossessed Indigenous peoples and cleared forests with abandon”. Research shows that, for 8,000 years after the glaciers of the last ice age retreated, forests in the Midwestern United States doubled in biomass (A. M. Raiho et al. Science 376, 1491–1495; 2022). Just 150 years of industrial logging and agriculture erased this carbon accumulation.

It takes a wood to raise a tree: a memoir
“Imperial conquests and industrial revolutions relied on timber,” Farmer writes. “Wood-stock long guns for capturing lands and peoples; naval vessels with mighty masts for transporting the enslaved and the harvests of their labor.” In New Zealand, European settlers decimated the majestic kauri trees, which can live for up to 2,000 years and that once covered 1.2 million hectares of land. The trees’ 50-metre-trunks became ships’ masts; their resin was made into varnish and linoleum.

Like pines, firs, spruces, cedars, cypresses and redwoods, kauri (Agathis australis) is a gymnosperm. These flowerless plants with naked seeds tend to grow slower and live longer than angiosperms, flowering plants that bear fruit. About 25 plant species — most of them conifers — can live for more than a millennium without human assistance, surviving in restricted, vulnerable habitats.

Farmer also offers a global survey of ancient trees that have been protected and exalted. They include olive trees of the Levant (Olea europaea); research published this year shows that these were domesticated about 7,000 years ago for their fruit and oil (D. Langgut and Y. Garfinkel Sci. Rep. 12, 7463; 2022). In Africa, the baobab (Adansonia sp.) is both the longest-lived tree and the largest, offering shade and shelter, foods, medicines and textiles. Enslaved Africans planted baobabs in the Caribbean; some survive still. Ginkgo biloba, a species that dates back 390,000 years, survived only in China, whence it was spread around the world in the past millennium. A grove of ginkgo trees survived the atomic bombing of Hiroshima in Japan in August 1945, pushing out new buds the following spring.

The planet’s current tree cover, Farmer writes, includes 3 trillion large plants covering about 30% of all land. It is, in fact, expanding. But the new cover consists mostly of shelter belts (trees planted to protect crops or animals), temperate-zone timber crops and tropical plantations of eucalyptus and palm oil. A shrinking proportion of tree cover is made up of species-rich old-growth communities.

Epic loss
“What would humans and nonhumans stand to lose if these survivors all died prematurely? A world of things,” Farmer writes. “Old trees sustain forest communities” with their seeds and litter. Other plants grow on them, and animals live in them. Their roots share nutrients with other organisms via underground fungi. Groups of “Old Ones” are carbon sinks. Large-scale monocultures are shorter-lived and take less greenhouse gas out of circulation.

But even bygone trees of the once-tropical Arctic might offer lessons for a warming world. Palaeobotanist Hope Jahren, in her 2016 memoir Lab Girl, describes how she spent three summers on Axel Heiberg Island, digging “through a hundred vertical feet of time”. Fir, cypress, larch, redwood, spruce, pine and hemlock trees populated this lush conifer forest, with an understory of angiosperms: maple, alder, birch, hickory, chestnut, beech, ash, holly, walnut, sweetgum, sycamore, oak, willow and elm. These plants thrived even through three months of winter darkness and three of constant summer light.

“Here stood one of the great forests of all time,” Farmer writes. Today, as the Arctic warms nearly four times as fast as any other place on Earth, the genomes of species related to the trees of this mummified forest might be adaptable enough for the trees to flourish in a rewarmed planet, he says. Old trees have much to teach us: we would be wise to listen.