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Heat stress and tree death won’t daunt Northbourne’s tree planting

Genevieve Jacobs 25 January 2019 136

An artists’ impression of how the eucalyptus mannifera will look surrounding the light rail route. File photo.

Despite death, decline and heat stress, Transport Canberra senior management say they remain confident that the eucalyptus mannifera specimens planted along Northbourne Avenue are the right choice for the light rail zone and will eventually thrive.

That claim has been disputed by an expert regional silviculturist who remains adamant that the trees are “doomed” and that planting advanced trees to satisfy public expectations demonstrates “a very basic lack of knowledge”.

Marcus Sainsbury, who is the senior manager design planning and environment for Transport Canberra wouldn’t put an exact number on the trees that are dying or likely to die along the Northbourne alignment although he conceded the long run of extremely high temperatures had been very stressful for the newly planted four-metre trees.

“There are two categories – the ones that are in permanent decline and ones that are under stress,” he said. “It’s fair to say that in general terms the industry would expect a 5 per cent loss of mature trees planted, and we’re confident that we are under that at the moment.

“Clearly some of the trees have died and by the same token, some of the trees under stress have made a recovery. We are monitoring the ones under stress and seeing how they go, maintaining a watering regime for the stressed trees over the past few weeks.”

Paradoxically, heavy surface watering can create shallow root systems and unsustainable growth because the trees aren’t anchored deeply. Mr Sainsbury says this is a fair observation but believes that the “bespoke” planting environment installed for each tree will solve any problems.

“We’ve used 30 cubic metres of growing medium for each tree, and that level of soil preparation was never undertaken in the past. Previous trees were sitting on a clay pan which meant that the roots spread out in shallow systems. But the manniferas have provision for deep-root watering, where the water is channelled down to the base of the tree pit to promote root growth.”

Mr Sainsbury says the growing environment should also prevent compression from construction traffic, parrying the suggestion that it’s a compromise to plant them out at this size rather than planting smaller trees.

It’s there that he differs considerably from independent silviculturist Peter Marshall, who runs TerraPreta truffles at Braidwood and has over 40 years of forestry experience. He believes more trees are doomed because of “this concept of growing a tree to be long and thin and whippy and putting it in to create an instant forest.

“It’s a construction zone with soil compaction and concrete in the soil so the PH will be very high from the leftover lime. The position is very exposed and there’s a massive swing in temperatures at ground level from day to night.

“Had they planted little dollar seedlings of the same species they would have grown a metre in every year,  at an astonishingly lower cost. This nursery-grown stock is four metres tall now, but they’ll possibly die under the stress of exposure, while the tubestock would get there quickly, with a much better root architecture and stability.

“Where is the survey that says the public want tall saplings that then die? Have they made this up in their own heads?”

Marshall is also critical of the species choice, saying the eucalypts risk shedding limbs as a matter of course. “High-temperature limb breakage is an ecological adaptation. A water column in the trunk literally explodes and detaches itself, which creates a hollow nesting place for birds and animals, whose manure then fertilises the tree. That’s a great ecosystem adaptation, but a massive disadvantage in an urban environment.”

In stark contrast, the tree planting process is characterised as “careful and deliberate” by Marcus Sainsbury. “Back in May 2017, we established a landscape trial plot that replicated in exact detail the planting arrangements for Northbourne. We are not watering the trial plots trees at all now and the regime has shown that those trees are doing really well”

Peter Marshall argues that deciduous trees, perhaps Mexican oaks from a very similar climate but with a much stronger root and branch structure would have been a better choice amidst Canberra’s magnificent tapestry of trees. But Marcus Sainsbury is adamant that the manniferas are the right choice and will thrive.

Do you think mature eucalypts were the right choice for the Northbourne corridor?

 


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136 Responses to Heat stress and tree death won’t daunt Northbourne’s tree planting
Rachel Sirr Rachel Sirr 11:58 pm 01 Feb 19

Number one- don't plant trees that will fall on the tram and kill people. Deciduous are more flexible and just like the old part of Canberra have had a touch of class.l

Robert Bendle Robert Bendle 12:09 am 01 Feb 19

Another waste of our money, go figure, please people of Canberra let’s get rid of this left wing government and get people who will work for the whole population of our great territory.

Elizabeth Ann Thurbon Elizabeth Ann Thurbon 7:58 pm 30 Jan 19

All the experts I know on native plantings have always said these trees were so wrong here. Rainer Rehwinkel

Idyllic Hills Wines Idyllic Hills Wines 5:29 pm 30 Jan 19

they are not just eucalypts - they are 'brittle gums", no less. one can only wonder why this was the preferred choice for a transport corridor

Douglas Lumsden Douglas Lumsden 5:00 pm 30 Jan 19

Get rid of the trees, as it will be huge cost to manage them in the future. Tram Power lines being destroyed in storms. Plant something else.

    Ashley Wright Ashley Wright 5:29 pm 30 Jan 19

    Douglas Lumsden trees won’t be falling on the power lines. If they start to hang over the track the will cut them back, just like they do for the main roads.

    Only risk is if the whole tree goes over. Sure it happens but not often.

Maelinar Maelinar 4:55 pm 30 Jan 19

They were probably told by the NCA that it had to be something native which would rule out the mexican alternative suggested by the other arborist, but there are probably better options. There’s a Maleluca that you can crop down to ground level that grows right on back that would have probably made a fantastic hedge, but my personal favourite is Acca sellowiana which is nearly as native as Russell Crowe and Crowded House and its suitable for the Canberra climate.

Either would work great as a huge (3+ metres) hedge or individual plants, without getting too high to be in the way for powerlines or obstructive for a tram.

    Capital Retro Capital Retro 10:13 pm 30 Jan 19

    This one ticks all the boxes and the spectacle of twin rows in-flower down Northbourne Avenue would be a bigger attraction than Floriade.

    ttps://www.nationalarboretum.act.gov.au/living-collection/trees/tree-descriptions/forests-and-trees/forest-51

    The National Arboretum has them and many are pl;anted in Canberra.

Capital Retro Capital Retro 3:55 pm 30 Jan 19

The Rainbow Roundabout and Manuka Oval look spic-and-span so stop complaining about all the other dirty sites.

George Brenan George Brenan 12:11 pm 30 Jan 19

Looks to me like an attention seeking arborist. Everyone so easy to assume that this was done without thought of consideration. Imagine the challenges of autumn leaf fall for example if deciduous trees were used.

    Jason Ezra Jason Ezra 10:01 pm 30 Jan 19

    George Brenan we could get Dept of Transport public servants out to collect the leaves as part of their service to the proletariat each day.

Paul Davis Paul Davis 9:18 am 30 Jan 19

Stupid people cut down the existing trees what doe you expect

    Peter Kelley Peter Kelley 11:45 am 01 Feb 19

    The original trees were dying anyway. The Northbourne trees have been replaced several times over their history.

Jo Byrne Jo Byrne 8:05 am 30 Jan 19

No I would have preferred deciduous trees. Eucalpyts are beautiful but do not lend themselves to formal planting ir in straight rows.

Taite Gregg Taite Gregg 6:30 am 30 Jan 19

Noooooooo

Sue Ellen Sue Ellen 6:26 am 30 Jan 19

Meanwhile visitors are reporting how dirty and rundown Canberra is becoming. The weeds, rubbish, and crumbling infrastructure make me mad I pay so much to live here. We used to be the jewel in Australia's crown but now we're a blight. Would it be so hard to employ some people to sweep and pressure wash the pavement in Civic on a regular basis or spray the weeds in the suburbs?

    Warren Morris Warren Morris 3:02 pm 30 Jan 19

    Sue Ellen I agree. The ACT Government don’t seem to think cleaning and city presentation are a priority. I remember how well cared for Canberra was in the 80s and 90s, then it’s been downhill ever since. 😔

    Elizabeth Ann Thurbon Elizabeth Ann Thurbon 7:56 pm 30 Jan 19

    Sue Ellen and the ACT Government need to manage all the individual owners in the Sydney and Melbourne buildings to do up these buildings as they are the heart of our city and are in a disgraceful state of repair. Imagine the glorious old buildings being the main attraction at the centre of our city if the ACT government restored them and enlivened them and their laneways.

    Julie Macklin Julie Macklin 12:59 am 31 Jan 19

    Elizabeth Ann Thurbon Something is happening to the Sydney building. Photograph taken about a month ago.

Tanya Buckley Tanya Buckley 6:24 am 30 Jan 19

Sherrie what we have been talking about.

    Sherrie Mackey Sherrie Mackey 6:27 am 30 Jan 19

    Tanya Buckley mmm. Not their smartest choice.

Margot Sirr Margot Sirr 11:15 pm 29 Jan 19

Gums fall and lose limbs regularly. Are they a wise choice for the tram run?

Greig Spencer Greig Spencer 10:51 pm 29 Jan 19

Eucalypts have no place in suberbia. There are lots of other trees or shrubs that look and suit the landscape better.

Jorge Garcia Jorge Garcia 10:19 pm 29 Jan 19

YES.

I read an article in TCT that interviewed the arborist that had been engaged to supply and plant the trees. Genevieve would have done well to interview them as well. They have been planning this for years... Growing the young trees in hessian to encourage deep roots and best chance for survival. Some losses are inevitable and allowances are made for that... The arboretum assume about 20% loss and if its lower they actually cull some trees to make room for the ones that are more likely to be successful.

As for heat stress and lack of water... Hasn't anyone noticed that its been a VERY wet summer?

Mannifera grow up to be large beautiful trees with a white trunk and bright green foliage and an interesting branch structure. They will support native birds and other creatures. Planting established trees is a good way to speed the overall effect. As for dropping branches... That can be managed as no doubt it will in such a prominent location.

Capital Retro Capital Retro 10:10 pm 29 Jan 19
Brydie Kelly Brydie Kelly 10:07 pm 29 Jan 19

Eventually thrive? They're already dead though 🤔 and what happens when they grow too close to the overhead wires? Will they just tear them down too?

David Green David Green 9:58 pm 29 Jan 19

The root ball for a tree is 100mm for every 10mm so how much room do these trees have from the road and footpaths

    Ashley Wright Ashley Wright 6:48 pm 31 Jan 19

    David Green about 1.5m. Which is about the same distance the gums on the outside of Northborne Ave are away from the road and footpath.

    JC JC 10:22 am 30 Jan 19

    Lucky then that the trees they are planting are not deciduous then.

    Capital Retro Capital Retro 3:50 pm 30 Jan 19

    Obviously you have no idea how many dead leaves eucalyptus trees drop naturally (this is the main fire litter in the bush) and then there are the green twigs and leaves that the parrots and white cockatoos will be responsible for (when they aren’t chewing on the electrical fittings).

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