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

Genevieve Jacobs 25 January 2019 131

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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131 Responses to Heat stress and tree death won’t daunt Northbourne’s tree planting
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
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).

Rhonda Maxwell Rhonda Maxwell 8:45 pm 29 Jan 19

These trees have a shallow root system. They are a problem waiting to happen. A large storm, there will be trees knocked down and limbs on the tram tracks or the electrical wiring.

Bronwyn Meredith Bronwyn Meredith 7:39 pm 29 Jan 19

I think eucalypts were a stupid choice for a main road and rail line. The gardens look very uninspiring.

Shannon Dooley Shannon Dooley 7:31 pm 29 Jan 19

What a waste of money this is

Lucy Baker Lucy Baker 7:23 pm 29 Jan 19

That artist’s impression doesn’t look realistic. Who is going to keep fallen branches off the tracks?

    Capital Retro Capital Retro 8:46 pm 29 Jan 19

    It looks like someone has planted a tardis up the track.

    JC JC 8:47 pm 29 Jan 19

    Maybe the same people who keep fallen branches off the roads all over Canberra.

    Maelinar Maelinar 4:47 pm 30 Jan 19

    Thats a mix between the ACTSES and the Firies, but gardening is done by Parks and Wildlife I think. Cross-jurisdictional nightmare right there.

    They might want to create a new garden and wildlife management service to handle the tram lines and then the rabbit population that will move straight on in from across the road at the legislative assembly to that nice lovely patch of garden along the entire tram line up Northbourne to Mitchell.

Elizabeth Martin Elizabeth Martin 7:22 pm 29 Jan 19

I hope when they die they use the space for a bike lane

Mathew Stephenson Mathew Stephenson 6:58 pm 29 Jan 19

Typical Canberra. We do the ruddy landscaping before we finish the actual project. It’s a joke as the weed growth on the light rail strip already demonstrates

    Ashley Wright Ashley Wright 8:56 pm 29 Jan 19

    Mathew Stephenson I notice on Flemington road they have had to dig up quite a stretch of the landscaping right beside the track. Almost like they are adding in another conduit.

Kerry Mulgrue Kerry Mulgrue 6:48 pm 29 Jan 19

Yeah, I noticed the dying saplings on my way to work this morning.

Margaret Freemantle Margaret Freemantle 6:37 pm 29 Jan 19

A total debarcle -obvously not trained hortlculturalists. Planting amidst the mess,the dirt the noise etc -no respect for a living thing or how these plants need care.. So many have died -such a huge waste of money and a real disgrace. I saw them being watered at 3pm on the 41 degree heat da -any rookie knows that is a no no.

Beck Bianco Beck Bianco 6:35 pm 29 Jan 19

I’m not expert but a) gum trees are designed to thrive in Australia heat b) terrible choice because they notoriously have branches fall off and split in storms so I hope the trees do die and the public servant behind this one consult an expert on what should be planted.

Capital Retro Capital Retro 6:27 pm 29 Jan 19

It’s hard to tell if more trees are expiring on Northbourne Avenue or at the Arboretum Theme Park.

Louis Sotiropoulos Louis Sotiropoulos 6:07 pm 29 Jan 19

I'd rather believe the local expert than the incompetent transport Canberra

Aldith Graves Aldith Graves 5:30 pm 29 Jan 19

Not planted at the heat of summer

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