The quietly radical plan to make all of Christchurch a 'leafy' suburb

Saturday, 24 February 2024

When it comes to shade, Christchurch is a city of haves and have-nots. Charlie Mitchell reports.

On a blistering summer afternoon, a sweaty journalist sprawled beneath a giant lime tree and felt the cool grass bristling on his neck.

Nearby, a family picnicked beneath a cinnamon-coloured maple. Kids wrestled with a pudgy golden retriever beneath a colossal pin-oak. Even a short and squat yew tree was called into service, shading a wooden bench and its snoozing occupant.

Shade has been a hot commodity in Christchurch this summer, which is on track to be one of the hottest in recorded history. It has led many to practise Shinrin-yoku, or “forest bathing” - relaxing in a forested environment to escape city life.

To observe this phenomenon, The Press visited Abberley Park in St Albans on one of the hottest days of summer.

The park was once a private garden, brought into public ownership in 1939. At the time, the city feared losing its trees: “Closer settlement of the city and suburbs inevitably meant the sacrifice of a large number of trees which gave Christchurch one of its charms,” a city official said in 1943.

“The preservation of such places as Abberley Park … become of correspondingly greater importance.”

That foresight is why, more than 80 years later, scores of people could bathe in the shade of its towering trees, some nearly as old as the city itself. The appeal is visceral: Confronted with a row of stately lime trees, even this reporter couldn’t resist the call of Shinrin-yoku.

A different scene played out that same afternoon in the city’s west.

At Tautoro Park in Wigram Skies, the pounding sun had warmed the pavement. Light glanced off the windows of large, low-slung houses, baking in the sun. The grass was the colour of wet cardboard.

Wigram Skies was developed in the 2010s on a former air base. It has plenty of open space scattered across multiple parks; fitting with the ethos of its developer, Ngāi Tahu, it has pockets of native plants and an impressive wetland swale.

What it’s missing is shade.

The Press could not find a single person in Wigram Skies’ open spaces. Many, it seemed, had sought the air-conditioned safety of the local supermarket.

Cities produce an “urban heat island” effect, in which they become noticeably hotter than surrounding areas, particularly if they lack trees. At Tautoro Park, the temperature reading was 32C, but it felt much hotter.

These two extremes represent a problem: When it comes to shade, Christchurch is a city of haves and have nots. It is most obvious at the height of summer: Some areas have plenty of large trees, and some have barely any.

“It is absolutely true - there are fairly stark differences in canopy cover throughout the city,” says Dr Justin Morgenroth, an Associate Professor in the School of Forestry at the University of Canterbury.

Morgenroth has documented this phenomenon in his research.

The “haves”, in this case, are the older, inner-city suburbs surrounding Abberley Park: St Albans, Merivale and Fendalton. Their tree canopy coverage - meaning the area covered by foliage at least 3.5m tall - ranges between 15% and 20%

Among the “have-nots” are newer, further afield communities, often bordering industrial areas: Wigram, Hornby and Aranui. Their tree canopy coverage is between 5% and 10%.

It is mostly a consequence of time. Wigram Skies has trees - tōtara, kōwhai and lancewoods flank its streets - but they are slow growing and will take decades to produce shade. Unlike the older parts of the city, it was built when New Zealanders preferred large houses, often at the expense of smaller backyards. There simply isn’t enough room for large trees.

These lower canopy areas bring down Christchurch’s overall coverage, which in 2018 was about 13.5%. Globally, this is poor: Morgenroth compared canopy coverage in more than 120 cities and found Christchurch ranked in the bottom quarter.

Even for cities in “grassland” areas - places not naturally abundant in forest - Christchurch was below average. The city with the most comparable coverage was Albuquerque, New Mexico, which fans of the TV series Breaking Bad will recall is in a desert.

This data confirmed a long-held suspicion: That Christchurch, despite its Garden City moniker, has struggled to incorporate large trees into its growth, and continues to do so. We inherited scraps of forest like Abberley Park, but have failed to pay it forward as the city sprawled outwards.

It is not just an aesthetic problem; trees have a range of benefits that are typically unaccounted for. They clean the air and provide habitat for birds and insects; they absorb planet-heating carbon, soften the fall of heavy rain and provide bubbles of quiet in bustling suburbs.

On hot days, they give valuable shade, and cool the air through evapotranspiration. With enough trees, you can lower a suburb’s average temperature, counteracting the effects of a warming world.

Many of these benefits increase when a tree has a large leaf area.

“As trees increase in size, there’s an almost exponential increase in leaf area, and that’s why larger trees don’t just provide three or four or five times the benefit of smaller trees - they provide an exponentially larger amount of benefit,” Morgenroth says.

Housing pressures and modern development patterns are unfavourable to large trees: New developments, with smaller sections, may include a handful of small trees, but they will not provide the benefit of one large tree.

Perhaps most importantly, trees make people happy. In 2015, the city council in Melbourne gave each of its trees an email address so residents could report damage.

Instead, the trees were bombarded with fan letters.

“We know that human wellbeing is affected by the landscape,” says Dr Colin Meurk, a landscape ecologist.

“Just being able to have greenery around you - whether it’s open space, prairies and savannahs, and woodland or forest - all contribute to that physiological and mental wellbeing. There’s plenty of literature now that supports that general view.”

Growing awareness of these benefits has led to a reconsideration for the value of urban forest.

Last year, Parliamentary Commissioner for the Environment Simon Upton called upon councils to better protect green spaces, and treat them as a core service: “They are a form of infrastructure every bit as important as pipes and roads,” he said.

And so, in this context, Christchurch took up the challenge. How can the whole city become a “leafy suburb”?

Urban Forest Plan

Standing on a footpath in industrial Aranui, “leafy” is not a word that comes to mind.

The eastern suburb is mostly residential, except for an industrial pocket of concrete and metal plonked amid houses. It is a harsh environment, with few trees and little green space.

There is, however, a small public park. Shortland Playground backs onto the hulking grey wall of the neighbouring Pak’nSave. On hot afternoons, it is drenched in sunlight. The grass is scorched. There are only a couple of trees that could, at a stretch, be accused of providing shade.

It is here that Toby Chapman, head arborist at the Christchurch City Council, meets The Press to explain the city’s urban forest plan. Passed last year, and drawing partly on Morgenroth’s work, it is the city’s formal response to its unequal tree coverage.

“It’s almost like a roadmap for how we want to manage our vegetation across the city,” Chapman says.

“Urban forest means all the vegetation across our urban environment - if you imagine taking away all the houses and things in a city, you would have a forest. The purpose of the urban forest plan is to create a larger urban forest, and not just to increase the size of it, but also its resilience as well.”

The plan, simply put, is this: Plant trees. Loads of them.

By 2070, the aim is to have 20% of the city covered in trees, and for no individual ward to have less than 15% coverage. If successful, it would make every ward nearly as leafy as Fendalton.

The high level figure may not sound ambitious - 20% is only slightly higher than Auckland’s existing tree coverage, and many cities have set higher targets - but it contains a quiet radicalism that will transform the city. By planting trees widely, rather than intensively, the benefits of trees will be shared.

The council is targeting 60 parks and reserves a year, the first tranche of which are under way. They run the gamut: At Parkland Reserve, a large sports ground, the plan is to plant 265 trees around existing sport fields. In the tiny Runnymede Reserve in Templeton, which is smaller than the average residential section, six trees are proposed.

Then, there is Shortland Playground. In the next 50 years, the humble park will transform. The plan is to plant 27 new trees, nearly a dozen taller than 10m. The park’s canopy coverage would rise from 4% to 25%: A desolate park will become a small forest on the fringe of industrial Aranui.

The intent, Chapman says, is to approach the project thoughtfully, and ensure the right tree is put in the right place. Every park planting goes out for public consultation, and comes with a detailed plan, noting where individual trees will go and how large they’ll be at maturity. They even include modelling showing where shade will be cast at various times of the year.

Most of the trees will come from the council’s own nursery, and will be cared for by a permanent in-house team for seven years, with regular watering and pruning, before entering the regular tree maintenance programme.

“It is, as far as I know, more comprehensive than anywhere else that does it,” Chapman says.

“If you give a tree the best start, you’ll get a much better outcome.”

Not universally loved

Changes of this scale, naturally, will bring conflict.

It is clear that many people value urban trees. Public submissions on the urban forest plan were overwhelmingly positive. When Greater Christchurch residents were asked what they most wanted in the city by 2050, the third highest priority (of 33 options) was “a lot of green space and trees”.

But trees are not universally beloved. They can block the sun in winter, and their roots can damage infrastructure. Leaves cause a mess.

Sometimes, people get so frustrated they vandalise trees. Like anything that occupies public space, trees are political.

“Not everybody sees trees as only good,” Morgenroth says.

At a community board meeting last year, some Wigram residents vented frustration about plans to plant trees in their neighbourhood.

Due to its poor canopy coverage, Wigram is a priority area: Four of its parks are in the first tranche of tree plantings.

The changes are extensive. Tautoru Park in Wigram Skies, which was baking under the sun last month, would be radically changed: 72 new trees are proposed, increasing its canopy coverage from 10% to 70%. Another park nearby would have 61 new trees, also increasing its canopy coverage to 70%.

Some of these trees will be more than 20m tall. Some neighbouring houses - specifically, during the winter solstice - would, for short periods, have their homes cast in darkness.

One affected resident, armed with a PowerPoint presentation, told the community board his home was designed to look upon an open reserve, not towering trees. Another worried the trees would bring “unsavoury elements” into the community.

A third, when asked whether smaller trees would be better, put it bluntly: “We’d rather have no trees in there.”

(Some trees have since been taken out of the plans.)

These conflicts will likely continue as the council moves through each of its more than 1200 parks and reserves. Chapman says the council wants to bring people along, and respond to concerns when they arise.

“We wanted to give the public confidence that we’re not just throwing trees in without giving it thought.

“We want trees planted that people want. We don’t want to create anxiety through our tree planting.”

Lost heritage

Centuries ago, before humans arrived and permanently transformed the landscape, what is now Christchurch was a complicated mosaic of vegetation: Largely open, covered in harakeke and grasses, with pockets of deep swamp and floodplain forest.

Almost all of it is gone now. We are left with reminders: Ancient forests buried beneath Cathedral Square, represented by the Chalice sculpture; the central city buildings built with native timber from the plundered Papanui Bush.

The coming wave of reforesting is an opportunity to restore some of this lost heritage.

“All trees, of course, generate ecosystem services, but indigenous species have a special gloss on that,” Meurk, the ecologist, says.

“I would argue they have cultural connection, they contribute tūrangawaewae (a place to stand), and they contribute to general identity with a local place … in other words, connection to the land, and connection to your specific land.”

The urban forest plan aims to have natives as 40% to 60% of new trees; Chapman says the plan is to put natives in high traffic areas.

He meets The Press at a park in Woolston, where a glimpse of this future is taking shape.

A line of kōwhai flank the main footpath, which cuts through open grass; a couple of tōtara stand sentinel by the playground. A line of cherry blossoms will give a pop of colour, as will some stately sweet gum trees, together a pop of gold, pink and red.

Cutler Park was one of the first planted under the forest plan. Less than a year on, the changes are easy to visualise.

New trees outnumber mature ones seven to one. Large trees, many of them natives, have been placed in prime position - a city that once used exotics as specimen trees is turning towards tōtara.

An area of open space is preserved: Everything else will be covered by tree canopy.

In a distant summer, future generations might reflect on the foresight of their forebears to pepper the city with trees, creating a network of Abberley Parks in miniature - ones infused with the history of the land.

“People tend not to act until it’s right in front of their eyes, unfortunately - that’s just a human characteristic, I suppose,” Meurk says.

“But as they say, the best time to plant a tree was 30 years ago, and the next best time is now. So let’s get on with it.”