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Native trees best suited to beat Canberra’s intensifying heat, says report

Ian Bushnell 14 October 2019 56

Oak trees provide a cooling canopy in summer. Photo: Michelle Kroll, Region Media.

The heat is on Canberra’s much-loved deciduous trees with a new report rating native varieties as the best species to cope with the ACT’s changing climate, with the kurrajong on top.

Commissioned by the ACT Government, the Urban Tree Species report from the ANU Fenner School of Research identified the best tree species to improve Canberra’s urban tree canopy and adapt to rising temperatures.

It comes after the release last month of Canberra’s Living Infrastructure Plan, alongside the ACT’s Climate Change Strategy, which outlined how the city can be cooled in a warming climate, including increasing urban tree canopy cover from 21 per cent to 30 per cent.

Using climate change models and species-specific data, the report reviewed the Transport Canberra and City Services (TCCS) tree list to determine which species will survive and thrive in Canberra’s climate change future, ranking species according to their climate suitability, capacity as street trees and advising which species are more suitable in certain scenarios.

It assessed and ranked tree species on a range of climate factors including drought tolerance, frost tolerance, extreme heat tolerance, weed potential and allergen potential.

The report assessed 211 tree species used in Canberra’s urban spaces and two lists, one climate-weighted, of top 50 species are dominated by native species, including eucalypts such as yellow box.

There are no exotic deciduous species in the top 10, but various drought-tolerant oaks and liquidamber are listed as well as the indigenous deciduous white cedar.

Other species include various pines and cypresses, crape myrtles, casuarina and acacia. It suggests trialling other native trees such as lemon-scented gum, spotted gum, wilga and silky oak, and even the purple flowering jacaranda which does well in Dubbo.

Despite its resilience and shady canopy, the report recommends popular oriental plane trees be used sparingly due to allergenic pollen.

The report selected trees as best to cope in a Canberra which is forecast to have a climate more like Dubbo, with temperatures up to 4 degrees Celsius higher by 2090. Although rainfall is tipped to remain steady, it will be delivered more in storm bursts than in soaking falls, where water is more likely to run off, particularly in paved environments.

The authors also rule out the mass irrigation of trees across the Canberra urban forest but argue for better planting methods and conditions, and greater stormwater retention.

They also argue for a greater diversity of plantings.

Associate Professor Cris Brack and Shane Rattenbury

Associate Professor Cris Brack and Climate Change Minister Shane Rattenbury.

The report warns that climate change, combined with urban heat island effects and the stress of built environments, may lead to large-scale tree and urban forest failure.

“In south-east Australian cities, the combination of heat output from built infrastructure and climate change-related variability in rainfall and temperature regimes mean that tree decline associated with increasing urban drought severity and frequency is a principal concern for urban tree managers,” it says.

While the report clearly favours native species, it says there are no trees on the TCCS list that are not suitable for Canberra.

Climate Change Minister Shane Rattenbury said the government wanted to plant a lot more trees to protect the city against rising temperatures.

“We need to make sure we’re planting the right ones,” he said. “It’s quite an important report and will help shape the future of this city in terms of what trees are being planted.”

Mr Rattenbury said the Government had not made an explicit decision to turn away from exotic deciduous species to give the urban forest a more native bent, saying the city needed different species in different places to serve different purposes.

“Many of the trees are reaching the end of their natural lives so we’re going to see change over the coming decades, having the community more involved will make that change easier,” he said.

He said the Government did want to get rid of exotic species but some won’t survive the heat.

“Canberrans really love that autumn landscape in the city. It’s not that we want to get rid of it, that’s where we’ll have to work very carefully. The report does identify some of those deciduous species that remain viable in Canberra. Some won’t because they won’t cope in the heat. They’re some of the decisions we’ll have to take,” he said.

Mr Rattenbury said the tree program was expensive and he would like to see more of the community involved at a neighbourhood level to determine what species are planted and how they are maintained, including watering.

We’re more likely to see more eucalypts like these. Photo: Michelle Kroll

He also flagged more onerous conditions for developers to ensure there is decent tree cover and that they are maintained for a time post-development.

“Ideas are being discussed, how do we keep them alive, and make the program more affordable,” he said. “I don’t think it’s the Government’s sole responsibility to deliver it,” Mr Rattenbury said.

One of the authors, Associate Professor Cris Brack, said there would be a mix of natives and exotics that would survive, and the more diversity the better.

But he said perceptions that all eucalypts were not as cooling as exotics were, dropped limbs and were more of a fire hazard were misplaced.

“There is a perception that eucalypts don’t shade as much as exotics, but they do have very important cooling and climate mitigation effects,” he said.

“Eucalypts don’t give much shade at midday but the really big cooling effect is evapotranspiration or how the water moves through the leaves and cools down. Shading is one component but evapotranspiration is a major component. Maybe midday is not the time we need the shade, maybe its morning and late afternoon, when we’re being active.”

He said there were 800 species of eucalypt so it would be a matter of improved tree selection.

Eucalypts in streetscapes were not a fire risk, but he said different species should be planted on the urban interface.

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56 Responses to Native trees best suited to beat Canberra’s intensifying heat, says report
Acton Acton 10:45 am 14 Dec 19

The problem with gum trees is they burn ferociously in the canopy contributing to ember spreads. So they add tremendous risk to suburban areas during our hotter times. The advantage of deciduous trees is felt immediately in the suburbs with lower temperatures and fire resistance. But the ACT Government is bound by ideology, not common sense.

Capital Retro Capital Retro 10:29 am 18 Oct 19

Why is the native tree Grevillea robusta (Silky Oak) always overlooked in these debates?

Philip Martin Philip Martin 7:45 pm 16 Oct 19

Surly we should follow the recommendations set out within the Urban Tree Species Report from the ANU Fenner School of Research. This document is based on the up-to-date science conducted by experts in urban forestry. I'm all for following science rather than opinions.

    Amanda Evans Amanda Evans 8:31 am 18 Oct 19

    Philip Martin I am qualified and there are many aspects to this than just one piece of research, with one particular focus. Yes, some of these native species might withstand CC better than some deciduous trees (although I have also read other research indicating that many eucs are also suffering), but we can't live in a city like Canberra with no sun into our private and public spaces in Winter. Also my comments are about creating better planned housing layouts where the space is provided to provide for large deciduous trees, both in gardens, in communal spaces and within the streetscape itself, to keep temps down in Summer and warm in Winter.

    Philip Martin Philip Martin 9:12 am 18 Oct 19

    I appreciate your opinion and am extremely happy to read any peer reviewed scientific reports you or anyone else has published, which clarifies the role that deciduous trees should occupy in Canberra. Thank you for your response.

Steve Herczeg Steve Herczeg 8:22 am 16 Oct 19

Hmmm. A report commissioned by the ACT Government to decide the future direction of urban tree planting initiatives?

Follow the money. Which species are cheaper to plant and maintain over the long-term future? Which species are cheaper during autumn?

As usual this has nothing to do with climate change and everything to do with cost savings.

    Martin McMaster Martin McMaster 11:36 am 16 Oct 19

    So how, in your view, can a government ever commission and/or respond to a report on anything?

    Martin McMaster Martin McMaster 11:36 am 16 Oct 19

    also can you be specific about the failings in the report that point to your "follow the money" assertion/

Gabriel Spacca Gabriel Spacca 1:41 am 16 Oct 19

Oh don’t worry. At the current rate of construction Canberra won’t have any trees left for this to be a problem.

liberalsocialist liberalsocialist 7:08 pm 15 Oct 19

Much prefer deciduous trees – and so do most people. Have a look at what people consider ‘premium’ suburbs with ‘leafy’ streets – whether in Canberra, Melbourne or Sydney. They’re full of Maples, Oaks, Cherry Blossoms, Liquid Ambers… anything but the gum tree’s that will take decades to mature along Northbourne, provide little shade, drop branches on trams and cars and, if they do attract native fauna, puts that fauna in the middle of two of the busiest sets of lanes in Canberra. Well done!

Steve Wood Steve Wood 11:07 am 15 Oct 19

Who cares... Andrew Barr and the ACT Govenrment are building large apartment buildings and want us living in concrete jungles...

    Nate Jennings Nate Jennings 11:24 am 15 Oct 19

    Steve Wood would you rather more urban sprawl that destroys more of the environment?

    Julie Macklin Julie Macklin 1:06 pm 15 Oct 19

    Nate Jennings I actually believe that some people would rather there was urban sprawl and more of the environment was bulldozed.

    Dan Connolly Dan Connolly 6:02 pm 16 Oct 19

    Nate Jennings what environment most of Canberra and surround are ex bloody sheep paddocks.

Martin McMaster Martin McMaster 10:51 am 15 Oct 19

I'll be interested to read this report. I know it is about choice of planting but I wonder if there is comment about preserving trees. Trees that are already mature and doing well on a site should stay there whatever their species. They reduce urban heat and help bind the soil as well as posessing whatever amenity they were planted to achieve.

Stephen Matthews Stephen Matthews 10:16 am 15 Oct 19

Go for a drive round older suburbs and see the dirty mess street gumtrees leave.They are not a suitable street tree

Julie Macklin Julie Macklin 9:30 am 15 Oct 19

Native trees are fine planted where they don't shade homes. Near houses the trees need to be deciduous, so the sun can get through in winter.

    Stephen Matthews Stephen Matthews 10:18 am 15 Oct 19

    No dirty gums

    Julie Macklin Julie Macklin 10:23 am 15 Oct 19

    Stephen Matthews I find (most; not all) gums are fine away from houses and I don't find most of them "dirty". The problem for me with them, is that they aren't deciduous and still shade in winter.

    Peter Mackay Peter Mackay 10:58 am 15 Oct 19

    Yes. Gums have their place. They are good fits for native bird populations, for example. In parkland, on the verges of main roads, banks of waterways. Just not near houses.

Bill Gemmell Bill Gemmell 8:05 am 15 Oct 19

Doesn't matter how many and what type of tree is chosen, they need to be planted correctly and looked after, including sufficient water and nutrients and soil compaction prevented. This Government's record on urban trees is appalling.

    Ian McLeod Ian McLeod 8:13 am 15 Oct 19

    Bill Gemmell it would help if we got rain

    Bill Gemmell Bill Gemmell 8:15 am 15 Oct 19

    Ian McLeod true, but established trees actually don't require that much moisture really.

    Peter Mackay Peter Mackay 8:18 am 15 Oct 19

    It would help, but watering street trees in times of drought would keep them alive.

    Where did this mania to make Canberra grow ever larger come from, anyway?

    The idea was to have a federal capital to serve the nation. Now we have development to keep the local government in funds as services fall ever further behind.

    In 1986, when I came to Canberra, we had *more* buses than we do now, and it all worked like clockwork.

    Ian McLeod Ian McLeod 8:28 am 15 Oct 19

    Peter Mackay true. The ACT Government has gone rogue. Some things I support like high density (if anything it makes the place more vibrant) but other things like this anti-health anti-environment bright blue street lamps against all evidence are just odd. The ACT Government waves its "Green" credentials around but scratch the surface and it starts to look a little hollow.

    Ian McLeod Ian McLeod 8:29 am 15 Oct 19

    Bill Gemmell they do, it just takes longer to kill them.

    Bill Gemmell Bill Gemmell 8:35 am 15 Oct 19

    Ian McLeod of course you can hurry it all up by parking your SUV in the root zone

    Ian McLeod Ian McLeod 8:53 am 15 Oct 19

    Bill Gemmell please don't encourage them.

    Peter Mackay Peter Mackay 10:48 am 15 Oct 19

    Ian McLeod High and medium densities have their place. Look at some of the older cities in Europe. I love the Parisian model, repeated endlessly: five storey apartments, shops and restaurants on the bottom, lots of small parks, wide boulevards and narrow lanes. Close to work, close to public transport. People don’t need cars for everyday use.

    But how much work is there in Gungahlin? People have to get in their cars to go anywhere. So the narrow streets are choked with parked cars. Neighbours dispute over parking spaces. Nature strips are thin and used for car parking.

    Amanda Evans Amanda Evans 8:32 am 18 Oct 19

    Bill Gemmell you are absolutely correct. We don't do trees well here anymore.

Amanda Evans Amanda Evans 7:49 am 15 Oct 19

If the city was better planned to allow for larger trees in backyards and streets, this wouldn't be such a problem.

Eucalypts are not suitable urban trees in Canberra. They are good shade in Summer, but make all spaces too cold and dark in Winter and they shed all year and drop limbs. Aside from that, they block solar panels in Winter.

We are much better served with ample amounts of deciduous trees where we get the benefit of Summer shade and Winter sun.

The fact that we are suffering from heat island effect comes down to poor planning and blocks and streets that don't allow for landscape, greedy developers, who push for max yield at the expense of good design and amenity and homes that are just too big for the block they're on.

In the older suburbs and in parts of Tuggeranong, where gardens are actually gardens, the temperatures can be up to 10 degrees lower in Summer.

A healthy urban forest is critical to our future sustainability, but eucalyptus trees near homes are not the answer.

    Stephen Matthews Stephen Matthews 10:19 am 15 Oct 19

    Couldnt agree more.There is a place for gums and it is not as a street tree

Stephen Saunders Stephen Saunders 7:15 am 15 Oct 19

Sorry, Prof Brack, as you can already see, your “facts” and “evidence” bounce straight off Australians’ irrational hatred of Australian flora and fauna.

They can’t cope with eight syllables in “evapotranspiration”. They’d much rather be cleaning up acorns and oak-leaves all year.

    liberalsocialist liberalsocialist 7:04 pm 15 Oct 19

    Have you ever considered that a lot of people prefer the look of a lot of non-Australian species? They have richer colours with deeper greens and reds primarily. I’m one of them.

    Just because you like them, doesn’t make anyone preferring non-Australian varieties as ‘irrational’. That in itself is irrational thinking at its best.

actcyclist actcyclist 6:20 am 15 Oct 19

It’s pretty obvious that native trees are more resilient, but did they even consider that they provide poor shade in summer?
There’s nothing like a solid row of deciduous trees for cooling a street

Peter Mackay Peter Mackay 3:46 am 15 Oct 19

Bugger them. Deciduous trees work best here. This is the dogmatic anti-people brigade making a grab.

In summer, we have shade. In winter the sun shines through.

With gum trees, the reverse, and they drop branches on people.

Canberra is a city full of people, with buildings and roads and parks. It’s never going to be the sort of virgin bushland these people want, and Australia has plenty of bush.

    Guy Be Guy Be 7:26 am 15 Oct 19

    The report is about the suitability of the trees for climate, rather than how good they are at shaping a pleasant climate for people. Deciduous trees that are all dead because it's too hot for them don't provide much summer shade.

    Peter Mackay Peter Mackay 7:31 am 15 Oct 19

    Deciduous trees seem to be thriving in Canberra's summers. Have done for a hundred years. Just how stupid are these people not to look out of the window?

    Cathy Dearnley Cathy Dearnley 7:34 am 15 Oct 19

    Peter ... at a recent presentation by ACT govt they discussed the importance of deciduous trees for exactly the reasons you give. They're not morons... but realists trying to provide the best canopy for Canberra. The best canopy in their calculations must include alive! Some deciduous trees haven't been successful yet in the crowded suburbs of Gungahlin, the pears have good options. Don't assume you're the only one thinking

    Amanda Evans Amanda Evans 7:50 am 15 Oct 19

    Guy Be and how did that happen?

    Peter Mackay Peter Mackay 7:55 am 15 Oct 19

    Cathy Dearnley Gungahlin is an example of profit-driven planning, rather than people-oriented. Narrow, crowded streets etc.

    Filling remote suburbs full of cheap medium-density merely replicates the social problems we see everywhere else in the world where government thinks that’s a cool idea.

    Picking a tree species won’t fix the underlying problems.

    Ian McLeod Ian McLeod 8:16 am 15 Oct 19

    I agree with Peter Mackay, the government's own thermal mapping showed the eucalyptus provide only marginal abatement of the heat island effect. Perhaps we could have both? But deciduous trees do provide better shade in summer which we will need increasingly more.

    Peter Mackay Peter Mackay 8:20 am 15 Oct 19

    Gum trees turn their leaves parallel to the sun's rays in summer. They actually minimise shade.

    Stephen Matthews Stephen Matthews 10:18 am 15 Oct 19

    Peter Mackay houses taking up all the building block.they are just big home units

    Jacqui Owen Jacqui Owen 9:09 pm 16 Oct 19

    and eucalypts don't provide moist leaf litter, they are considered an environmental weed in most of the world.

    In Brazil, they plant the tree they want, a eucalypt, nitrogen fixing plant and a chop and drop crop in the same hole.

    Then they trim all the laterals on the gum to impede its aliopathic properties and when it has grown to 3ft or 6ft they cut it out and use for building.

    Its purpose was to bring water up to the other plants roots and help them establish. ie pioneer plant.

Jack Hearps Jack Hearps 9:49 pm 14 Oct 19

This report and its recommendations are a crucial resource. Collecting and using storm water run off is essential . For instance in Dunlop there is a series of shallow run off ditches which have no trees planted in them. Lost opportunity for free watering. There is also quite a few dead trees that have yet to be replaced. Likewise trees provide excellent wind breaks and on certain days we have very hot dry winds that should be met on the outter city fronts with specific tree types. Under canopy shrubs are also essential and i suggest they be noted also.

Stuart Roesler Stuart Roesler 8:56 pm 14 Oct 19

Get rid of those damn fluff trees! Terrible choice of tree.

    Amanda Evans Amanda Evans 8:37 am 18 Oct 19

    Stuart Roesler the fluff is for about a week and they don't cause allergies either.

    For the rest if the tear, the White Poplar is a stunning addition to Canberra's landscape.

    Stuart Roesler Stuart Roesler 8:40 am 19 Oct 19

    Amanda Evans. I disagree. They cause hell with allergies. And it lasts longer. I ride everyday through the rubbish and it has been going on for at least 3 weeks. I have hay fever everyday and it's a huge contributor. Not very nice when it gets up your nose while riding.

    Marilyn Bradbury Marilyn Bradbury 8:29 am 14 Dec 19

    Amanda Evans the 'fluff' off the poplars does cause allergies and causes havoc for both drivers and riders! Additionally ask some shop owners in the area where the fluff gathers in the shops! These ugly trees need to be replaced.

Annette Milnes Annette Milnes 8:14 pm 14 Oct 19

Deciduous trees survive very well and allow sun in winter and much better shade in summer, as well as making neater street trees.

    Alison Brittliff Alison Brittliff 4:18 pm 15 Oct 19

    Annette Milnes I prefer deciduous too, kambah is gums but it’s colder in the shade in winter

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